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This paper investigates the global stratospheric Brewer-Dobson circulation (BDC) in the ERA5 meteorological reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF). The analysis is based on simulations of stratospheric mean age of air, including the full age spectrum, with the Lagrangian transport model CLaMS, driven by winds and total diabatic heating rates from the reanalysis. ERA5-based results are compared to those of the preceding ERA–5 Interim reanalysis. Our results show a significantly slower BDC for ERA5 than for ERA–Interim, manifesting in weaker diabatic heating rates and larger age of air. In the tropical lower stratosphere, heating rates are 30–40% weaker in ERA5, likely correcting a known bias in ERA–Interim. Above, ERA5 age of air appears slightly high-biased and the BDC slightly slow compared to tracer observations. The age trend in ERA5 over 1989–2018 is negative throughout the stratosphere, as climate models predict in response to global warming. However, the age decrease is not linear over the period but exhibits steplike 10 changes which could be caused by muti-annual variability or changes in the assimilation system. Over the 2002–2012 period, ERA5 age shows a similar hemispheric dipole trend pattern as ERA–Interim, with age increasing in the NH and decreasing in the SH. Shifts in the age spectrum peak and residual circulation transit times indicate that reanalysis differences in age are likely caused by differences in the residual circulation. In particular, the shallow BDC branch accelerates similarly in both reanalyses while the deep branch accelerates in ERA5 and decelerates in ERA–Interim.
Highlights
• Extreme weather events (floods, droughts, extreme heat) impact freshwater ecosystems.
• Effects of extreme events are site-specific, varying by organism traits and site hydrography.
• Cumulative impact of events is more significant than single events' magnitude.
• Temporal dynamics and biological characteristics are crucial for evaluating impacts.
• Freshwater ecosystem resilience depends on complex factors, not just event severity.
Abstract
Understanding the impacts of extreme weather events on freshwater ecosystems is imperative during a time when a multitude of challenges compromises these environments' health. Exploring how such events affect macroinvertebrate communities in rivers sheds light on the resilience of freshwater ecosystems, which is essential for human well-being and biodiversity conservation. In this study, long-term time series of benthic macroinvertebrate communities from four sites along three freshwater streams within the Rhine-Main-Observatory Long-Term Ecological Research site in Germany were analyzed. Each of them was sampled annually over a span of ~20 years to assess the impacts of extreme weather events (floods, droughts, and extreme heat) on macroinvertebrate communities. The findings reveal that the effects of extreme events are site-specific, suggesting that the impacts of an extreme event can vary based on several potential factors, including the life history traits of the organisms within the community and, among others, the hydrography of the site. Moreover, the analysis highlights that the cumulative impact of these events over time is more significant than the impact of a single event's magnitude, while following distinct temporal dynamics. This underscores the importance of considering both the temporal dynamics and the biological characteristics of communities when evaluating the consequences of extreme weather events on biodiversity, illustrating that the resilience of freshwater ecosystems and their biodiversity under such conditions depends on a complex interplay of factors rather than the severity of individual events.
Marine stratocumuli are the most dominant cloud type by area coverage in the Southern Ocean (SO). They can be divided into different self-organized cellular morphological regimes known as open and closed mesoscale-cellular convective (MCC) clouds. Open and closed cells are the two most frequent types of organizational regimes in the SO. Using the liDAR-raDAR (DARDAR) version 2 retrievals, we quantify 59 % of all MCC clouds in this region as mixed-phase clouds (MPCs) during a 4-year time period from 2007 to 2010. The net radiative effect of SO MCC clouds is governed by changes in cloud albedo. Both cloud morphology and phase have previously been shown to impact cloud albedo individually, but their interactions and their combined impact on cloud albedo remain unclear.
Here, we investigate the relationships between cloud phase, organizational patterns, and their differences regarding their cloud radiative properties in the SO. The mixed-phase fraction, which is defined as the number of MPCs divided by the sum of MPC and supercooled liquid cloud (SLC) pixels, of all MCC clouds at a given cloud-top temperature (CTT) varies considerably between austral summer and winter. We further find that seasonal changes in cloud phase at a given CTT across all latitudes are largely independent of cloud morphology and are thus seemingly constrained by other external factors. Overall, our results show a stronger dependence of cloud phase on cloud-top height (CTH) than CTT for clouds below 2.5 km in altitude.
Preconditioning through ice-phase processes in MPCs has been observed to accelerate individual closed-to-open cell transitions in extratropical stratocumuli. The hypothesis of preconditioning has been further substantiated in large-eddy simulations of open and closed MPCs. In this study, we do not find preconditioning to primarily impact climatological cloud morphology statistics in the SO. Meanwhile, in-cloud albedo analysis reveals stronger changes in open and closed cell albedo in SLCs than in MPCs. In particular, few optically thick (cloud optical thickness >10) open cell stratocumuli are characterized as ice-free SLCs. These differences in in-cloud albedo are found to alter the cloud radiative effect in the SO by 21 to 39 W m−2 depending on season and cloud phase.
Seismic arrays provide tools for the localization of events without clear phases or events outside the network, where the station coverage prohibits classical localization techniques. Beam forming allows the determination of the direction (back azimuth) and horizontal (apparent) velocity of an incoming wavefront. Here we combine multiple arrays to retrieve event epicentres from the area of intersecting beams without the need to specify a velocity model. The analysis is performed in the time domain, which allows selecting a relatively narrow time window around the phase of interest while preserving frequency bandwidth. This technique is applied to earthquakes and hybrid events in the region of Fogo and Brava, two islands of the southern chain of the Cape Verde archipelago. The results show that the earthquakes mainly originate near Brava, whereas the hybrid events are located on Fogo. By multiple-event beam stacking we are able to further constrain the epicentral locations of the hybrid events in the northwestern part of the collapse scar of Fogo. In previous studies, these events were attributed to shallow hydrothermal processes. However, we obtain relatively high apparent velocities at the arrays, pointing to either deeper sources or complex ray paths. For a better understanding of possible errors of the multi-array analysis, we also compare slowness values obtained from the array analysis with those derived from earthquake locations from classical (local network) localizations. In general, the results agree well. Nevertheless, some systematic deviations of the array-derived back-azimuth and slowness values occur that can be quantified for certain event locations.
Seismic arrays provide tools for the localization of events without clear phases or events outside the network, where the station coverage prohibits classical localization techniques. Beam forming allows the determination of the direction (back azimuth) and horizontal (apparent) velocity of an incoming wavefront. Here we combine multiple arrays to retrieve event epicentres from the area of intersecting beams without the need to specify a velocity model. The analysis is performed in the time domain, which allows selecting a relatively narrow time window around the phase of interest while preserving frequency bandwidth. This technique is applied to earthquakes and hybrid events in the region of Fogo and Brava, two islands of the southern chain of the Cape Verde archipelago. The results show that the earthquakes mainly originate near Brava, whereas the hybrid events are located on Fogo. By multiple-event beam stacking we are able to further constrain the epicentral locations of the hybrid events in the northwestern part of the collapse scar of Fogo. In previous studies, these events were attributed to shallow hydrothermal processes. However, we obtain relatively high apparent velocities at the arrays, pointing to either deeper sources or complex ray paths. For a better understanding of possible errors of the multi-array analysis, we also compare slowness values obtained from the array analysis with those derived from earthquake locations from classical (local network) localizations. In general, the results agree well. Nevertheless, some systematic deviations of the array-derived back-azimuth and slowness values occur that can be quantified for certain event locations.
We evaluate the influence of a forest parametrization on the simulation of the boundary layer flow over moderate complex terrain in the context of the Perdigão 2017 field campaign. The numerical simulations are performed using the Weather Research and Forecasting model in large eddy simulation mode (WRF-LES). The short-term, high-resolution (40 m horizontal grid spacing) and long-term (200 m horizontal grid spacing) WRF-LES are evaluated for an integration time of 12 h and 1.5 months, respectively, with and without forest parameterization. The short-term simulations focus on low-level jet events over the valley, while the long-term simulations cover the whole intensive observation period (IOP) of the field campaign. The results are validated using lidar and meteorological tower observations. The mean diurnal cycle during the IOP shows a significant improvement of the along-valley wind speed and the wind direction when using the forest parametrization. However, the drag imposed by the parametrization results in an underestimation of the cross-valley wind speed, which can be attributed to a poor representation of the land surface characteristics. The evaluation of the high-resolution WRF-LES shows a positive influence of the forest parametrization on the simulated winds in the first 500 m above the surface.
We evaluate the influence of a forest parametrization on the simulation of the boundary layer flow over moderate complex terrain in the context of the Perdigão 2017 field campaign. The numerical simulations are performed using the Weather Research and Forecasting model in large eddy simulation mode (WRF-LES). The short-term, high-resolution (40 m horizontal grid spacing) and long-term (200 m horizontal grid spacing) WRF-LES are evaluated for an integration time of 12 h and 1.5 months, respectively, with and without forest parameterization. The short-term simulations focus on low-level jet events over the valley, while the long-term simulations cover the whole intensive observation period (IOP) of the field campaign. The results are validated using lidar and meteorological tower observations. The mean diurnal cycle during the IOP shows a significant improvement of the along-valley wind speed and the wind direction when using the forest parametrization. However, the drag imposed by the parametrization results in an underestimation of the cross-valley wind speed, which can be attributed to a poor representation of the land surface characteristics. The evaluation of the high-resolution WRF-LES shows a positive influence of the forest parametrization on the simulated winds in the first 500 m above the surface.
Marine stratocumuli are the most dominant cloud type by area coverage in the Southern Ocean (SO). They can be divided into different self-organized cellular morphological regimes known as open and closed mesoscale-cellular convective (MCC) clouds. Open and closed cells are the two most frequent types of organizational regimes in the SO. Using the liDAR-raDAR (DARDAR) version 2 retrievals, we quantify 59 % of all MCC clouds in this region as mixed-phase clouds (MPCs) during a 4-year time period from 2007 to 2010. The net radiative effect of SO MCC clouds is governed by changes in cloud albedo. Both cloud morphology and phase have previously been shown to impact cloud albedo individually, but their interactions and their combined impact on cloud albedo remain unclear.
Here, we investigate the relationships between cloud phase, organizational patterns, and their differences regarding their cloud radiative properties in the SO. The mixed-phase fraction, which is defined as the number of MPCs divided by the sum of MPC and supercooled liquid cloud (SLC) pixels, of all MCC clouds at a given cloud-top temperature (CTT) varies considerably between austral summer and winter. We further find that seasonal changes in cloud phase at a given CTT across all latitudes are largely independent of cloud morphology and are thus seemingly constrained by other external factors. Overall, our results show a stronger dependence of cloud phase on cloud-top height (CTH) than CTT for clouds below 2.5 km in altitude.
Preconditioning through ice-phase processes in MPCs has been observed to accelerate individual closed-to-open cell transitions in extratropical stratocumuli. The hypothesis of preconditioning has been further substantiated in large-eddy simulations of open and closed MPCs. In this study, we do not find preconditioning to primarily impact climatological cloud morphology statistics in the SO. Meanwhile, in-cloud albedo analysis reveals stronger changes in open and closed cell albedo in SLCs than in MPCs. In particular, few optically thick (cloud optical thickness >10) open cell stratocumuli are characterized as ice-free SLCs. These differences in in-cloud albedo are found to alter the cloud radiative effect in the SO by 21 to 39 W m−2 depending on season and cloud phase.
During winter 2015/2016, the Arctic stratosphere was characterized by extraordinarily low temperatures in connection with a very strong polar vortex and with the occurrence of extensive polar stratospheric clouds. From mid-December 2015 until mid-March 2016, the German research aircraft HALO (High Altitude and Long-Range Research Aircraft) was deployed to probe the lowermost stratosphere in the Arctic region within the POLSTRACC (Polar Stratosphere in a Changing Climate) mission. More than 20 flights have been conducted out of Kiruna, Sweden, and Oberpfaffenhofen, Germany, covering the whole winter period. Besides total reactive nitrogen (NOy), observations of nitrous oxide, nitric acid, ozone, and water were used for this study. Total reactive nitrogen and its partitioning between the gas and particle phases are key parameters for understanding processes controlling the ozone budget in the polar winter stratosphere. The vertical redistribution of total reactive nitrogen was evaluated by using tracer–tracer correlations (NOy–N2O and NOy–O3). The trace gases are well correlated as long as the NOy distribution is controlled by its gas-phase production from N2O. Deviations of the observed NOy from this correlation indicate the influence of heterogeneous processes. In early winter no such deviations have been observed. In January, however, air masses with extensive nitrification were encountered at altitudes between 12 and 15 km. The excess NOy amounted to about 6 ppb. During several flights, along with gas-phase nitrification, indications for extensive occurrence of nitric acid containing particles at flight altitude were found. These observations support the assumption of sedimentation and subsequent evaporation of nitric acid-containing particles, leading to redistribution of total reactive nitrogen at lower altitudes. Remnants of nitrified air masses have been observed until mid-March. Between the end of February and mid-March, denitrified air masses have also been observed in connection with high potential temperatures. This indicates the downward transport of air masses that have been denitrified during the earlier winter phase. Using tracer–tracer correlations, missing total reactive nitrogen was estimated to amount to 6 ppb. Further, indications of transport and mixing of these processed air masses outside the vortex have been found, contributing to the chemical budget of the winter lowermost stratosphere. Observations within POLSTRACC, at the bottom of the vortex, reflect heterogeneous processes from the overlying Arctic winter stratosphere. The comparison of the observations with CLaMS model simulations confirm and complete the picture arising from the present measurements. The simulations confirm that the ensemble of all observations is representative of the vortex-wide vertical NOy redistribution.
Emissions of the potent greenhouse gas perfluorocyclobutane (c-C4F8, PFC-318, octafluorocyclobutane) into the global atmosphere inferred from atmospheric measurements have been increasing sharply since the early 2000s. We find that these inferred emissions are highly correlated with the production of hydrochlorofluorocarbon-22 (HCFC-22, CHClF2) for feedstock (FS) uses, because almost all HCFC-22 FS is pyrolyzed to produce (poly)tetrafluoroethylene ((P)TFE) and hexafluoropropylene (HFP), a process in which c-C4F8 is a known by-product, causing a significant fraction of global c-C4F8 emissions. We find a global emission factor of ∼0.003 kg c-C4F8 per kilogram of HCFC-22 FS pyrolyzed. Mitigation of these c-C4F8 emissions, e.g., through process optimization, abatement, or different manufacturing processes, such as refined methods of electrochemical fluorination and waste recycling, could reduce the climate impact of this industry. While it has been shown that c-C4F8 emissions from developing countries dominate global emissions, more atmospheric measurements and/or detailed process statistics are needed to quantify c-C4F8 emissions at country to facility levels.
Surface temperature is a fundamental parameter of Earth’s climate. Its evolution through time is commonly reconstructed using the oxygen isotope and the clumped isotope compositions of carbonate archives. However, reaction kinetics involved in the precipitation of carbonates can introduce inaccuracies in the derived temperatures. Here, we show that dual clumped isotope analyses, i.e., simultaneous ∆47 and ∆48 measurements on the single carbonate phase, can identify the origin and quantify the extent of these kinetic biases. Our results verify theoretical predictions and evidence that the isotopic disequilibrium commonly observed in speleothems and scleractinian coral skeletons is inherited from the dissolved inorganic carbon pool of their parent solutions. Further, we show that dual clumped isotope thermometry can achieve reliable palaeotemperature reconstructions, devoid of kinetic bias. Analysis of a belemnite rostrum implies that it precipitated near isotopic equilibrium and confirms the warmer-than-present temperatures during the Early Cretaceous at southern high latitudes.
Particulate matter (PM) largely consists of secondary organic aerosol (SOA) that is formed via oxidation of biogenic and anthropogenic volatile organic compounds (VOCs). Unambiguous identification of SOA molecules and their assignment to their precursor vapors is a challenge that has so far only succeeded for a few SOA marker compounds, which are now well characterized and (partly) available as authentic standards. In this work, we resolve the complex composition of SOA by a top-down approach based on a newly created aerosolomics database, which is fed by non-target analysis results of filter samples from oxidation flow reactor experiments. We investigated the oxidation products from the five biogenic VOCs α-pinene, β-pinene, limonene, 3-carene, and trans-caryophyllene and from the four anthropogenic VOCs toluene, o-xylene, 1,2,4-trimethylbenzene, and naphthalene. Using ultra-high performance liquid chromatography coupled to a high-resolution (Orbitrap) mass spectrometer, we determine the molecular formula of 596 chromatographically separated compounds based on exact mass and isotopic pattern. We utilize retention time and fragmentation mass spectra as a basis for unambiguous attribution of the oxidation products to their parent VOCs. Based on the molecular-resolved application of the database, we are able to assign roughly half of the total signal of oxygenated hydrocarbons in ambient suburban PM2.5 to one of the nine studied VOCs. The application of the database enabled us to interpret the appearance of diurnal compound clusters that are formed by different oxidation processes. Furthermore, the application of a hierarchical cluster analysis (HCA) on the same set of filter samples enabled us to identify compound clusters that depend on sulfur dioxide mixing ratio and temperature. This study demonstrates how aerosolomics tools (database and HCA) applied on PM filter samples can improve our understanding of SOA sources, their formation pathways, and temperature-driven partitioning of SOA compounds.
Particulate matter (PM) largely consists of secondary organic aerosol (SOA) that is formed via oxidation of biogenic and anthropogenic volatile organic compounds (VOCs). Unambiguous identification of SOA molecules and their assignment to their precursor vapors are challenges that have so far only succeeded for a few SOA marker compounds, which are now well characterized and (partly) available as authentic standards. In this work, we resolve the complex composition of SOA by means of a top-down approach based on the newly created Aerosolomics database, which is fed by non-target analysis results of filter samples from oxidation flow reactor experiments. We investigated the oxidation products from the five biogenic VOCs α-pinene, β-pinene, limonene, 3-carene, and trans-caryophyllene and from the four anthropogenic VOCs toluene, o-xylene, 1,2,4-trimethylbenzene, and naphthalene. Using ultrahigh-performance liquid chromatography coupled to a high-resolution (Orbitrap) mass spectrometer, we determine the molecular formula of 596 chromatographically separated compounds based on exact mass and isotopic pattern. We utilize retention time and fragmentation mass spectra as a basis for unambiguous attribution of the oxidation products to their parent VOCs. Based on the molecular-resolved application of the database, we are able to assign roughly half of the total signal of oxygenated hydrocarbons in ambient suburban PM2.5 to one of the nine studied VOCs. The application of the database enabled us to interpret the appearance of diurnal compound clusters that are formed by different oxidation processes. Furthermore, by performing a hierarchical cluster analysis (HCA) on the same set of filter samples, we identified compound clusters that depend on sulfur dioxide mixing ratio and temperature. This study demonstrates how Aerosolomics tools (database and HCA) applied to PM filter samples can improve our understanding of SOA sources, their formation pathways, and temperature-driven partitioning of SOA compounds.
In the deep-sea, the interaction between benthic fauna and substrate mainly occurs through bioturbational processes which can be preserved as traces (i.e., lebensspuren). Lebensspuren are common features of deep seafloor landscapes and usually more abundant than the organism that produce them (i.e., tracemakers), rendering them promising proxies to infer biodiversity. The density and diversity relationships between lebensspuren and benthic fauna are to the present day unclear and contradicting hypotheses have been proposed suggesting negative, positive, or even null correlations. To test these hypotheses, in this study lebensspuren, tracemakers (specific epibenthic fauna that produce these traces), degrading fauna (benthic fauna that can erase lebensspuren), and fauna in general were characterized taxonomically at eight deep-sea stations in the Kuril Kamchatka Trench area. No general correlation (over-all study area) could be observed between diversities of lebensspuren, tracemakers, degrading fauna and fauna. However, a diversity correlation was observed between specific stations, showing both negative and positive correlations depending on: 1) the number of unknown tracemakers (especially significant for dwelling lebensspuren); and 2) the lebensspuren with multiple origins; and 3) tracemakers that can produce different lebensspuren. Lebensspuren and faunal density were not correlated. However, lebensspuren density was either positively or negatively correlated with tracemaker densities, depending on the lebensspuren morphotypes. A positive correlation was observed for resting lebensspuren (e.g., ophiuroid impressions, Actinaria circular impressions), while negative correlations were observed for locomotion-feeding lebensspuren (e.g., echinoid trails). In conclusion, lebensspuren diversity may be a good proxy for tracemaker biodiversity when the lebensspuren-tracemaker tandem can be reliable characterized; and lebensspuren-density correlations vary depending the specific lebensspuren residence time, tracemaker density and associated behaviour (rate of movement), but on a global scale abiotic and other biotic 42 factors may also play an important role.
In the deep sea, interactions between benthic fauna and seafloor sediment primarily occur through bioturbation that can be preserved as traces (i.e. lebensspuren). Lebensspuren are common features of deep-sea landscapes and are more abundant than the organisms that produce them (i.e. tracemakers), rendering lebensspuren promising proxies for inferring biodiversity. The density and diversity relationships between lebensspuren and benthic fauna remain unclear, and contradicting correlations have been proposed (i.e. negative, positive, or even null correlations). To approach these variable correlations, lebensspuren and benthic fauna were characterized taxonomically at eight deep-sea stations in the Kuril-Kamchatka Trench area, together with two novel categories: tracemakers (specific epibenthic fauna that produce these traces) and degrading fauna (benthic fauna that can erase lebensspuren). No general correlation (overall study area) was observed between diversities of lebensspuren, tracemakers, degrading fauna, and fauna. However, a diversity correlation was observed at specific stations, showing both negative and positive correlations depending on: (1) the number of unknown tracemakers (especially significant for dwelling lebensspuren); (2) the lebensspuren with multiple origins; and (3) tracemakers that can produce different lebensspuren. Lebensspuren and faunal density were not correlated. However, lebensspuren density was either positively or negatively correlated with tracemaker densities, depending on the lebensspuren morphotypes. A positive correlation was observed for resting lebensspuren (e.g. ophiuroid impressions, Actiniaria circular impressions), while negative correlations were observed for locomotion-feeding lebensspuren (e.g. echinoid trails). In conclusion, lebensspuren diversity may be a good proxy for tracemaker biodiversity when the lebensspuren–tracemaker relationship can be reliable characterized. Lebensspuren–density correlations vary depending on the specific lebensspuren residence time, tracemaker density, and associated behaviour (rate of movement). Overall, we suggest that lebensspuren density and diversity correlations should be studied with tracemakers rather than with general benthic fauna. On a global scale, abiotic (e.g. hydrodynamics, substrate consistency) and other biotic factors (e.g. microbial degradation) may also play an important role.
Measurements of vertical velocity from vertically pointing Doppler lidars are used to derive the profiles of vertical velocity variance. Observations were taken during the FESSTVaL (Field Experiment on Submesoscale Spatio-Temporal Variability in Lindenberg) campaign during the warm seasons of 2020 and 2021. Normalized by the square of convective velocity scale, the average vertical velocity variance profile follows the universal profile of Lenschow et al. (1980), however, daily profiles still show a high day-to-day variability. We found that moisture transport and the content of moisture in the boundary layer could explain the remaining variability of the normalized vertical velocity variance. The magnitude of the normalized vertical velocity variance is highest on clear-sky days, and decreases as the relative humidity increase and surface latent heat flux decrease in cloud-topped and rainy days. This suggests that moisture content and moisture transport are limiting factors for the intensity of turbulence in the convective boundary layer. We also found that the intensity of turbulence decreases with an increase in boundary layer cloud fraction during FESSTVaL, while the latent heating in the cloud layer was not a relevant source of turbulence in this case. We conclude that a new vertical velocity scale has to be defined that would take into account the moist processes in the convective boundary layer.
Measurements of vertical velocity from vertically pointing Doppler lidars are used to derive the profiles of normalized vertical velocity variance. Observations were taken during the FESSTVaL (Field Experiment on Submesoscale Spatio-Temporal Variability in Lindenberg) campaign during the warm seasons of 2020 and 2021. Normalized by the square of the convective velocity scale, the average vertical velocity variance profile follows the universal profile of Lenschow et al. (1980). However, daily profiles still show a high day-to-day variability. We found that moisture transport and the content of moisture in the boundary layer could explain the remaining variability of the normalized vertical velocity variance. The magnitude of the normalized vertical velocity variance is highest on clear-sky days and decreases as the absolute humidity increases and surface latent heat flux decreases on cloud-topped days. This suggests that moisture content and moisture transport are limiting factors for the intensity of turbulence in the convective boundary layer. We also found that the intensity of turbulence decreases with an increase in the boundary layer cloud fraction during FESSTVaL, while the latent heating in the cloud layer was not a relevant source of turbulence in this case. We conclude that a new vertical velocity scale has to be defined that would take into account the moist processes in the convective boundary layer.
A comprehensive study of sillenite Bi12SiO20 single-crystal properties, including elastic stiffness and piezoelectric coefficients, dielectric permittivity, thermal expansion and molar heat capacity, is presented. Brillouin-interferometry measurements (up to 27 GPa), which were performed at high pressures for the first time, and ab initio calculations based on density functional theory (up to 50 GPa) show the stability of the sillenite structure in the investigated pressure range, in agreement with previous studies. Elastic stiffness coefficients c11 and c12 are found to increase continuously with pressure while c44 increases slightly for lower pressures and remains nearly constant above 15 GPa. Heat-capacity measurements were performed with a quasi-adiabatic calorimeter employing the relaxation method between 2 K and 395 K. No phase transition could be observed in this temperature interval. Standard molar entropy, enthalpy change and Debye temperature are extracted from the data. The results are found to be roughly half of the previous values reported in the literature. The discrepancy is attributed to the overestimation of the Debye temperature which was extracted from high-temperature data. Additionally, Debye temperatures obtained from mean sound velocities derived by Voigt-Reuss averaging are in agreement with our heat-capacity results. Finally, a complete set of electromechanical coefficients was deduced from the application of resonant ultrasound spectroscopy between 103 K and 733 K. No discontinuities in the temperature dependence of the coefficients are observed. High-temperature (up to 1100 K) resonant ultrasound spectra recorded for Bi12MO20 crystals revealed strong and reversible acoustic dissipation effects at 870 K, 960 K and 550 K for M = Si, Ge and Ti, respectively. Resonances with small contributions from the elastic shear stiffness c44 and the piezoelectric stress coefficient e123 are almost unaffected by this dissipation.
Sedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using IntCal20 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1676 records (entities) from 1480 sites worldwide. The database (RPDv1b – Harrison et al., 2021) is available at https://doi.org/10.17864/1947.000345.
New U–Pb ages of detrital and igneous zircons of the Uppermost Unit of Crete shed light on its provenance and on Eohellenic to Eoalpine imprints in the eastern Mediterranean. The detrital zircons of all nappes show Variscan ages and are characterized by a Minoan-type age spectrum, which is typical for the NE margin of Gondwana. Parts of the metasedimentary rocks are unexpectedly young. Their detrital zircon ages continue via the Permian until the Late Triassic, Middle Jurassic and Early Cretaceous. The high-grade metamorphic rocks of the Asterousia crystalline complex are likely equivalents of the low-grade metamorphic trench and fore-arc deposits of the Vatos nappe pointing to Late Cretaceous slab roll back. The presence of both late Permian detrital zircons and Late Cretaceous arc-type granitoids suggest that the Uppermost Unit of Crete is derived from the late Permian/Late Cretaceous magmatic belt situated north of the Sava–Vardar–Izmir–Ankara Suture in the Strandja–Rhodope area. To achieve their recent position on Crete, the nappes had to travel more than 500 km. The traveling path is well tracked by rocks of the Upper Cycladic Unit, which are similar to those of the Uppermost Unit of Crete. The large displacement of the Cretan nappes was controlled not only by nappe transport, but probably also by dextral strike–slip along the North Anatolian Fault Zone and related counterclockwise rotation of the Anatolian block since the Eocene.
Highlights
• Solidification and cooling of an intruded dyke or sill within the middle or shallow crust generate stresses of order 200 MPa, which relax on time scales of a few years to million years.
• Stresses may exceed the brittle strength forming tensile fractures.
• Combined with the pressure gradient within the over-pressurized felsic melts, this explains the migration of felsic contact melt into shrinkage cracks (Sederholm-type veins).
Abstract
Rapid emplacement of a mafic dyke or sill at mid-crustal depth heats and possibly melts the felsic wall rock followed by solidification. Associated volume changes generate stresses, possibly enforcing brittle failure and melt migration. We model the evolution of melting, solidification, temperature, and stress including visco-elastic relaxation in 1D - dykes or -sills using realistic rock rheologies of the Weschnitz pluton (Odenwald). For deep emplacement (Case 1, 15.3 km) extensive contact melting of the wall rock occurs, for shallow emplacement (Case 2, 10 km) it is negligible. The stresses are zero at high melt fractions, but increase during solidification and cooling: The intrusion orthogonal stress is always zero. The intrusion parallel stress σ‖ within the intrusion is tensile (O(200 MPa)). It relaxes on a time scale between a few years (Case 1) and 0.6 m.y. (Case 2). Within the wall rock σ‖ is compressive during heating, but becomes tensile under solidification and cooling. Wall rock stresses relax on a time scale of months to 100 years. A Deborah number is defined based on viscous to thermal relaxation allowing generalization of our results. Adding lithostatic stresses, the total stresses of Case 1 remain below the brittle strength, while for Case 2 they may exceed it. Adding the lithostatic pressure to the melt pressure, the effective stresses exceed the brittle strength and intrusion orthogonal tensile fractures are predicted. Combined with the pressure gradient within the over-pressurized felsic melts generated in the wall rock, this explains the migration of felsic contact melt into shrinkage cracks of the mafic sill in the Weschnitz pluton.
Carbonate archives record a brief snapshot of the ambient Earth’s surface conditions at their deposition. However, the geologically reasonable extraction and interpretation of geochemical proxy data from ancient, diagenetically altered rock archives is fraught with problems. Three issues stand out: the dichotomy between petrographic and geochemical alteration; the lack of quantitative age constraints for specific diagenetic phases resulting in a poorly constrained admixture of local, basin-wide and over-regional (far-field) features; and an often insufficient understanding of the temperatures and compositions of diagenetic fluids. Here, the archive of Devonian marine limestones exposed to multiple far-field diagenetic events is used as an example to explore the above-listed issues. Methods applied include petrography, micro XRF, fluid inclusion data, clumped isotopes, δ13C and δ18O isotopes, 87Sr/86Sr ratios and quartz trace element data. Devonian limestones studied here were overprinted by two cross-cutting regional fault zones (T ≈ 230 °C) by multiple events between the Variscan Orogeny and the late Paleogene. The following processes are recorded: (i) protolith deposition and partial dolomitisation during rapid burial in the Middle/Late Devonian (T ≈ 180 °C); (ii) deep burial to ca 6.5 km and tectonic/hydrothermal overprint during the Variscan Orogeny in the Carboniferous (T ≈ 90–230 °C); (iii) rapid uplift to 1–2 km burial depth at the end of the Variscan Orogeny and hypogene karstification (T ≈ 50 to 100 °C) initiated by regional geology in the Permian/Triassic; (iv) tectonic/hydrothermal overprint during the opening of the Proto-Atlantic Ocean between the Early Jurassic and the Early Cretaceous (T ≈ 50 to 130 °C); (v) tectonic/hydrothermal overprint including renewed hypogene karstification and hydrothermal calcite cement precipitation (T ≈ 50 to 180 °C) during Alpine Orogeny between the Late Cretaceous and late Paleogene. Despite this complex series of diagenetic events, the protolith limestones largely preserved their respective Middle/Late Devonian dissolved inorganic carbon (DIC) and 87Sr/86Sr signatures. This study documents that geochemical proxy data, placed into their petrographic, paleotemperature, and local to over-regional context, significantly increases the ability to extract quantitative information from ancient carbonate rock archives. Research shown here has wider relevance for carbonate archive research in general.
Ecophysiological studies on Antarctic cryptophytes to assess whether climatic changes such as ocean acidification and enhanced stratification affect their growth in Antarctic coastal waters in the future are lacking so far. This is the first study that investigated the combined effects of increasing availability of pCO2 (400 and 1000 µatm) and irradiance (20, 200 and 500 μmol photons m−2 s −1) on growth, elemental composition and photophysiology of the Antarctic cryptophyte Geminigera cryophila. Under ambient pCO2, this species was characterized by a pronounced sensitivity to increasing irradiance with complete growth inhibition at the highest light intensity. Interestingly, when grown under high pCO2 this negative light effect vanished and it reached highest rates of growth and particulate organic carbon production at the highest irradiance compared to the other tested experimental conditions. Our results for G. cryophila reveal beneficial effects of ocean acidification in conjunction with enhanced irradiance on growth and photosynthesis. Hence, cryptophytes such as G. cryophila may be potential winners of climate change, potentially thriving better in more stratified and acidic coastal waters and contributing in higher abundance to future phytoplankton assemblages of coastal Antarctic waters.
Highlights
• Constrictional structures range from dome-and-basin folds to coeval folds and boudins.
• Under bulk constriction, the competent layer rotates slower than a passive plane.
• Extension-parallel and –perpendicular folds grow simultaneously.
• Extension-perpendicular folds affect previous boudins.
Abstract
We conducted scaled analogue modelling to show the influence of varying single layer initial orientation on the geometry of folds and boudins in a bulk constrictional strain field. The initial angle between the plane of shortening and the competent layer (θZ(i)) was incrementally increased from 0° to 90° by multiples of 11.25°. While the amount of layer thickening decreased with increasing θZ(i), the deformation structures produced range from pure dome-and-basin folds to coeval folds and boudins. Based on the attitude of fold axes, there are extension-parallel (FEPR) and extension-perpendicular (FEPP) folds, with axes subparallel and subperpendicular to the principal stretching axis (X), respectively. Coeval growth of FEPR folds and boudins occurred when θZ(i) > ca. 25°. The FEPP folds can be subdivided into a first type which affect the entire layer (if θZ(i) ranges between 11.25 and 78.75°) and a second type, referred to as FBEPP folds, which are affecting pre-existing boudins if θZ(i) > 45°. The interlimb angle of all types of folds increases with increasing θZ(i). Folds and boudins similar to the ones produced in this study can be found in salt domes and in tectonites of subduction zones.
Non-matrix-matched calibration of laser ablation ICPMS (trace/major) element data is a common quantification strategy. However, LA sampling is associated with downhole elemental fractionation, potentially causing inaccuracies if the magnitude of fractionation between the sample and reference material (RM) differs. Here, we estimate fractionation factors (FFs) for different elements (El) in a range of RMs relative to NIST SRM610/612 (FFEl/Ca-NIST) and evaluate element-specific corrections for downhole fractionation using these measured FFEl/Ca-NIST. Significantly different mean El/Ca values were observed before and after correction, particularly for the alkali elements (all RMs), and B, Fe, and Zn (some RMs), notably improving accuracy, especially for the alkali elements. In cases where this methodology does not result in an accuracy improvement, this may help identify underlying issues in reported/reference values for RMs, given that this phenomenon should be accounted for. Overall, we recommend considering routine assessment of FFs and applying a FF correction to enhance data quality.
"High-aluminous coal" is an important coal kind and widely distributed in North China in age of Permo-Carboniferous period. To explore their occurrence state, a total of 15 harmful elements (Li, Ga, In, Cd, Cr, Pb, Be, Mn, Zn, Ag, Co, Ni, Cu, Ba and U) in the No.9 coal and No.11 coal collected from Pingshuo mining district were determined by inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscope with energy spectrum (SEM-EDX). The results showed that the content of Li, Ga, In, Pb, Ag and U were all exceed the world hard coal. In view of the result of clustering analysis within trace elements, it was found that Co, Ni, Zn, Cu, Ag and Cr were mainly associated with sulfide minerals due to their common sulfophilic property. Manganese was mainly occurred in carbonate minerals, while Ba, Cd and U were mainly associated with total minerals. In addition, Pb was related to sulfides and Be is mainly distributed in clay minerals. The enrichment of such harmful elements in Pingshuo coal was caused by the combined effect of transgression and input of terrestrial materials in the peat accumulation stage. Li, Ga, In and Ag have reached the harmful grade.
Partial melting of crustal and mantle rocks under pressure from impedance spectroscopy measurements
(2004)
The purpose of this work is to achieve a better understanding of the physical properties of rocks during partial melting processes. The electrical conductivity of some crustal and upper mantle rocks was measured prior and above the melting under pressure. The variations of the electrical conductivity were compared with the distribution of melt in partially molten rock samples. The electrical conductivity was estimated from the impedance spectroscopy at temperatures between 800 and 1450˚C and at pressures between 0.3 and 2 GPa. These measurements were performed in a piston cylinder apparatus. At temperatures above the melting, samples were equilibrated during a long time and subsequently quenched. Thin sections were prepared and topology, volume fraction and chemical composition of melt was analyzed by using a microprobe. Above the solidus temperature, the electrical conductivity increases for about 1 to 2 orders of magnitude in comparison with non-melted rocks. The "melt effect" seems to reflect the formation of an interconnected network of melt. When a complete melt connectivity is established, the charge transport follows the network of the formed melt films at grain boundaries. Usually, it takes a long time in order to reach a steady state of the electrical resistance in partially molten rocks. Only when a steady state of the electrical resistance is achieved, the bulk conductivity of a sample can be measured properly. The time-independent electrical conductivity were found only after 200 h of annealing time at a desired temperature.
Usually, the measurements of a dihedral angle on grain-liquid interfaces in rocks show that the wetting of grain faces start to develop at temperatures slightly above the solidus temperature. The development of these faces should lead to a continuous melt network even at small melt fractions of few wt.%. This result is not confirmed by our electrical conductivity measurements. The complete interconnection of the melt phase, which was mark by an increase of the electrical conductivity, corresponds to a temperature significantly above the solidus temperature, for at least 30-50˚C. The development of these faces stimulate a significant increase of the electrical conductivity, and corresponds to the occurence of at least 5 wt.% of a melt fraction. This result could be explained by deviations from the textural equilibrium of a melt phase topology in partially molten samples due to heterogeneous grain size distribution, misorientation of grains and anisotropy of the superficial energy of adjacent grain boundaries.
Some mixing models that allow to calculate the electrical conductivity of a composite as a function of a melt fraction were examined and the results of these calculations are discussed.
The experimental results were compared to the conductivity data obtained from magnetotelluric and electromagnetic measurements in the Northern part of mid-Atlantic ridge where a series of magma chambers are presumably located. There is a good agreement between our conductivity values for a melt fraction of 10-13 the conductivity estimated in the Reykjanes ridge zone.
Tectonics and geothermal gradients from subduction to collision in the NW Variscan Iberian Massif
(2022)
The earliest tectonometamorphic record of tectonic slices incorporated to the base of an orogen holds the key to understand how an orogen is built. The tectonic pile of the NW Iberian section of the Variscan Orogen includes tectonic slices separated by crustal-scale thrusts. The earliest tectonometamorphic record in the uppermost parautochthon is calculated at 11–14 kbar and 450–500°C (P-T gradient about 13°C/km), suggesting a subduction-related metamorphic recrystallization at lower pressure than the overlying Lower Allochthon. Early conditions calculated in the autochthon (9–10 kbar and 425–450°C; 16°C/km) point to a relatively ‘cold’ collisional setting. Higher thermal gradients obtained from some sections of the autochthon (11–12 kbar and 700–725°C; 21°C/km) and the Lower Parautochthon (7.5 kbar and 550–700°C; 24–31°C/km), correspond to more advanced and ‘hot’ stages of collision. New U–Pb monazite geochronology indicates a 318–311 Ma age for the final formation of HT domes in the region. We propose the rapid decrease in P-T gradient (from <10 to 16°C/km) documents a fail to sustain further burial along a regular subduction zone. We consider the subsequent increase in the geothermal gradient (from 16 to 31°C/km) as the culmination of previous crustal accretion and the onset of crustal underthrusting and later processes in a collisional stage. We propose these switches in the early tectonometamorphic record of individual tectonic slices as potential markers to track the transition from subduction to collision in collisional orogens.
While high-quality climate reconstructions of some past warm periods in the Cenozoic era now exist, the geological processes responsible for driving the observed longterm changes in atmospheric CO2 are not sufficiently well understood. The long-term change in atmospheric CO2 across the Cenozoic has been proposed to be driven by processes such as terrestrial weathering, organic carbon production and burial, reverse weathering, and volcanic degassing. One way of constraining the relative importance of the various driving forces proposed so far is to better understand the degree to which ocean chemistry has changed because the chemistry of seawater responds to geologic processes that drive atmospheric CO2. In addition, knowledge of the concentration of the major elements in seawater is crucial for accurately applying proxies such as those based on the boron isotopic composition and Mg/Ca of marine carbonates (a proxy for palaeo pH/CO2 and palaeotemperature, respectively). Previously reported records of seawater composition are primarily derived from fluid inclusions in marine evaporites; however, the results are sparse due to the limited availability of such deposits. In this thesis, changes in the Eocene seawater chemistry were reconstructed using trace element (elements/Ca) and isotopic (δ26Mg) proxies in a Larger Benthic Foraminifera (LBFs), i.e., Nummulites sp., to constrain the driving processes of long-term changes in seawater chemistry.
To achieve the objective of this thesis, first, a measurement protocol was established using LA-ICPMS to measure the K/Ca ratio simultaneously with other element/calcium ratios, which is challenging due to the interference of ArH+ on K+. Utilising this newly established measurement protocol, laboratory-cultured Operculina ammonoides grown at different seawater calcium concentrations ([Ca2+]), repeated at different temperatures, as well as modern O. ammonoides collected from different regions exhibiting a range of seawater parameters, were investigated. A significant correlation was observed between K/Casw and K/CaLBF, allowing K/CaLBF to potentially be used as a proxy for seawater major ion reconstructions. In addition, modern O. ammonoides demonstrated no significant influence of most seawater parameters (temperature, salinity, pH, or [CO32-]) on K/CaLBF. Modern O.
ammonoides were also assessed for their Mg isotopic composition (δ26Mg), revealing no significant effect of temperature or salinity on δ26MgLBF. Furthermore, the Mg isotopic fractionation in O. ammonoides was found to be close to that of inorganic calcite, indicating minimal vital effects in these large benthic foraminifera.
Operculina ammonoides is the nearest living relative of the abundant Eocene genus Nummulites, enabling the reconstruction of seawater chemistry using the calibration based on O. ammonoides. The trace elemental/calcium proxies, including Na/Ca, K/Ca, and Mg/Ca, as well as the δ26Mg proxy, were investigated in Eocene Nummulites. The result showed that during the Eocene, [Ca2+]sw was 1.6-2 times higher, while [K+]sw was ~2 times lower than the modern seawater composition. Furthermore, [Mg2+]sw decreased from the early Eocene (54.3− +9 7..69 mmol kg-1 at ~55 Ma) to Late Eocene (37.8− +4 4..3 4 mmol kg-1 at ~31 Ma), followed by
an increase toward modern seawater [Mg]. In contrast, the variability in δ26Mgsw values remained within a narrow range of ~0.3 ‰ throughout the Cenozoic. The reconstructed [Ca2+]sw agrees with the suggestion that Cenozoic seawater chemistry changes can be explained via a change in the seafloor spreading rate. When combined with existing records, the observed minimal change in δ26Mgsw with an increase in [Mg2+]sw suggests an additional possible role of a decrease in the formation of authigenic clay minerals coincident with the Cenozoic decline in deep ocean temperature, which is also supported by the increase in the [K+]sw reconstructed here for the first time. This finding highlights that the reduction in seafloor-spreading rate and decline in reverse weathering during the Cenozoic era has played a significant role in the evolution of seawater chemistry, emphasizing the importance of these processes in driving long-term changes in the carbon cycle.
Highlights
• We find DBrfluid/melt = 1.19 to 3.92 for experimental Br degassing from basalt magma into aqueous fluids.
• D <1 under almost dry conditions propose only little Br degassing for dry intra-plate volcanism relative to volcanic arcs.
• An annual global Br flux of 23.5–72.9 × 109 g/y into the atmosphere was calculated.
Abstract
We present the first in-situ partitioning data for bromine between a natural basaltic melt and a coexisting fluid. For this study hydrothermal diamond anvil cell experiments at pressures up to 1.7 GPa were conducted. We combined laser heating to melt the basalt glass with external heating to lower the temperature gradient in the cell and to initiate circulation for the aqueous fluid. Bromine concentrations were measured in-situ with X-ray fluorescence in the basaltic melts, glasses, and in the fluid. From the results we calculated partition coefficients of DBrfluid/melt = 1.19 to 3.92 in the range of 0.4 to 1 GPa for aqueous fluids. Experiments with neon as the surrounding fluid (DBrfluid/melt = 0.38 ± 0.01 at 1.1 GPa) suggest that Br-release from a basalt into volatiles that have no bonding affinity with Br is weak. This should be the case for dry intra-plate volcanic eruptions. From the experimentally gained partition coefficients and from global Br concentration values in melt inclusions of arc magmas, we calculated an annual global Br flux of 23.5–72.9 × 109 g/y.
We present a new experimental dataset on the impact of the heavy halogens chlorine, bromine and iodine on the Raman water bands concerning pressure and their concentration at room temperature. These experiments were conducted at ambient temperature, with variations in halogen concentration and pressure ranging from 0 to 1.4 GPa.
The strength of the Raman water band shift change increases with the ionic size from chlorine, over bromine, to iodine. Our experiments further demonstrate that increased pressure diminishes the impact of the halogen shift change to a varying extent for each of the three halogens. This finding can have significant implications for the salinity calculation of fluid inclusions in minerals such as quartz or olivine. Particularly in the low salinity range, the concentration can be markedly underestimated if the pressure effect is neglected. For experiments in diamond anvil cells involving halogens dissolved in water, the change in Raman water band shifts can serve either as a new tool to monitor pressure, or to monitor the salinity.
Upper mantle shear zones are complex systems where deformation is commonly closely interacting with metamorphic (solid-solid) and/or melt/fluid-rock reactions. Here, feedback processes between deformation, reactions, grain size reduction and phase mixing result in strain weakening and the localization of deformation. The expression of these interlinked processes is portrayed by the microfabrics of strained peridotites and pyroxenites. The present thesis is focusing on these processes and their impact on the deformation in three upper mantle shear zones situated in the peridotite massifs of Lanzo (Italian Alps), Erro-Tobbio (Italian Alps) and Ronda (Betic Cordillera, Spain). In all three shear zones, the presence of melt led to phase mixing either by interstitial crystallization of pyroxenes from a Si-saturated and partially also highly evolved melt or by melt-rock reactions of pyroxene porphyroclasts with a Si-undersaturated melt. The effect of melt on the localization of strain is twofold and variable. Enhanced deformation by melt-wetted boundaries is assumed for all shear zones. Additionally, phase mixing by crystallization of interstitial pyroxenes or melt-rock reactions reduce or maintain the grain size by the formation of fine grained neoblasts and secondary phase boundary pinning. In this regard, pre- to early syn-kinematic, map-scale percolation of OH-bearing, evolved melts in the NW Ronda peridotite massif and the associated crystallization of interstitial pyroxenes result in the activation of grain size sensitive deformation mechanisms in the entire melt-effected area. In the rocks collected at Erro-Tobbio, syn-kinematic melt-rock reactions of pyroxene porphyroclasts and Si-undersaturated melt led to the formation of ultramylonitic neoblast tails (grain size ~10 μm). Compared to the adjacent coarser-grained olivine-dominated matrix, the activation of diffusion creep led to an increase in the strain rate by an order of magnitude within interconnected ultramylonitic layers. Strain localization and softening in ultramylonitic layers are also documented in the Lanzo samples. Neoblast tails of pyroxene porphyroclasts were likewise identified as their precursor. The phase assemblage of the tails, including ortho- and clinopyroxene, olivine, plagioclase, and spinel (± amphibole), and their geochemical trends suggest, unlike in Erro-Tobbio, a formation by continuous net-transfer reactions enhanced by the spinel lherzolite to plagioclase lherzolite transition.
The new results obtained from the three studied shear zones underscore the importance of reactions for the interlinked processes of grain size reduction, phase mixing, strain localization and strain softening in upper mantle shear zones. Concerning strain localization, the nature of the reaction (solid-solid, melt/fluid-rock) seems to play a subordinate role compared to its timing. Pre- to early syn-kinematic melt-triggered reactions result in strain localization along map-scale shear zones. Late stage syn-kinematic melt-rock or metamorphic reactions under high stress conditions are capable of localizing the deformation along discrete, sub-centimeter thick ultramylonites.
Highlights
• We present the first results of a deep learning model based on a convolutional neural network for earthquake magnitude estimation, using HR-GNSS displacement time series.
• The influence of different dataset configurations, such as station numbers, epicentral distances, signal duration, and earthquake size, were analyzed to figure out how the model can be adapted to various scenarios.
• The model was tested using real data from different regions and magnitudes, resulting in the best cases with 0.09 ≤ RMS ≤ 0.33.
Abstract
High-rate Global Navigation Satellite System (HR-GNSS) data can be highly useful for earthquake analysis as it provides continuous high-frequency measurements of ground motion. This data can be used to analyze diverse parameters related to the seismic source and to assess the potential of an earthquake to prompt strong motions at certain distances and even generate tsunamis. In this work, we present the first results of a deep learning model based on a convolutional neural network for earthquake magnitude estimation, using HR-GNSS displacement time series. The influence of different dataset configurations, such as station numbers, epicentral distances, signal duration, and earthquake size, were analyzed to figure out how the model can be adapted to various scenarios. We explored the potential of the model for global application and compared its performance using both synthetic and real data from different seismogenic regions. The performance of our model at this stage was satisfactory in estimating earthquake magnitude from synthetic data with 0.07 ≤ RMS ≤ 0.11. Comparable results were observed in tests using synthetic data from a different region than the training data, with RMS ≤ 0.15. Furthermore, the model was tested using real data from different regions and magnitudes, resulting in the best cases with 0.09 ≤ RMS ≤ 0.33, provided that the data from a particular group of stations had similar epicentral distance constraints to those used during the model training. The robustness of the DL model can be improved to work independently from the window size of the time series and the number of stations, enabling faster estimation by the model using only near-field data. Overall, this study provides insights for the development of future DL approaches for earthquake magnitude estimation with HR-GNSS data, emphasizing the importance of proper handling and careful data selection for further model improvements.
PolarCAP – A deep learning approach for first motion polarity classification of earthquake waveforms
(2022)
Highlights
• We present PolarCAP, a deep learning model that can classify the polarity of a waveform with a 98% accuracy.
• The first-motion polarity of seismograms is a useful parameter, but its manual determination can be laborious and imprecise.
• We demonstrate that in several cases the model can assign trace polar-ity more accurately than a human analyst.
Abstract
The polarity of first P-wave arrivals plays a significant role in the effective determination of focal mechanisms specially for smaller earthquakes. Manual estimation of polarities is not only time-consuming but also prone to human errors. This warrants a need for an automated algorithm for first motion polarity determination. We present a deep learning model - PolarCAP that uses an autoencoder architecture to identify first-motion polarities of earth-quake waveforms. PolarCAP is trained in a supervised fashion using more than 130,000 labelled traces from the Italian seismic dataset (INSTANCE) and is cross-validated on 22,000 traces to choose the most optimal set of hyperparameters. We obtain an accuracy of 0.98 on a completely unseen test dataset of almost 33,000 traces. Furthermore, we check the model generalizability by testing it on the datasets provided by previous works and show that our model achieves a higher recall on both positive and negative polarities.
Highlights
• Germany plans more long-distances water transfers to secure drinking water supply.
• Long-distance water transfers can unfold lock-ins that limit adaptive water governance.
• Our interdisciplinary case study shows how lock-ins emerge over different spaces and times.
• Commercialisation of water but also local protests contributed to various lock-ins.
• We therefore call for context-specific assessments of potentials and risks of LDWT.
Abstract
Germany plans to expand water transfers over long distances in the light of numerous and pressing challenges for drinking water supply. Research on inter- and intrabasin water transfers warns, however, that major investments in large-scale infrastructure systems accompanied by institutional logics and political interests often lead to a so-called lock-in. As a consequence, long-distance water transfers can limit the potential for adaptive water governance in the involved supply areas over decades with negative impacts for people and the environment. By using a case study in Germany as an example, we researched when, where and how such lock-ins around long-distance water transfers emerge. In the infrastructural development of the Elbaue-Ostharz transfer system we found various lock-ins that overlap in space and time. Some are located at the centre others at the margins of the infrastructure and commercialization of the water sector as well as hydraulic and hygienic concerns interlock with local protests in a way that the expansion of the long-distance water transfer infrastructure is presented continuously as imperative. Our findings contribute to a relational understanding of lock-ins of long-distance water transfers as contingent and diverse processes. Given the widespread occurrence of lock-ins, we argue for a context-specific assessment of potentials and risks of long-distance water transfers in times of multiple crises.
Highlights
• New fumarole and thermal water data for Askja and Kverkfjöll volcanoes, Iceland.
• Data compared to modelled compositions and fluxes of magmatic gas.
• Fumarole compositions compatible with origin of CO2 and S from degassing intrusions.
• Intrusive magmatic fluxes sufficient to sustain hydrothermal fluxes of CO2 and S in Iceland
• Magma degassing insignificant/minor source of H2O and Cl to Icelandic hydrothermal fluids
Abstract
Mantle volatiles are transported to Earth's crust and surface by basaltic volcanism. During subaerial eruptions, vast amounts of carbon, sulfur and halogens can be released to the atmosphere during a short time-interval, with impacts ranging in scale from the local environment to the global climate. By contrast, passive volatile release at the surface originating from magmatic intrusions is characterized by much lower flux, yet may outsize eruptive volatile quantities over long timescales. Volcanic hydrothermal systems (VHSs) act as conduits for such volatile release from degassing intrusions and can be used to gauge the contribution of intrusive magmatism to global volatile cycles. Here, we present new compositional and isotopic (δD and δ18O-H2O, 3He/4He, δ13C-CO2, Δ33S-δ34S-H2S and SO4) data for thermal waters and fumarole gases from the Askja and Kverkfjöll volcanoes in central Iceland. We use the data together with magma degassing modelling and mass balance calculations to constrain the sources of volatiles in VHSs and to assess the role of intrusive magmatism to the volcanic volatile emission budgets in Iceland.
The CO2/ΣS (10−30), 3He/4He (8.3–10.5 RA; 3He/4He relative to air), δ13C-CO2 (−4.1 to −0.2 ‰) and Δ33S-δ34S-H2S (−0.031 to 0.003 ‰ and −1.5 to +3.6‰) values in high-gas flux fumaroles (CO2 > 10 mmol/mol) are consistent with an intrusive magmatic origin for CO2 and S at Askja and Kverkfjöll. We demonstrate that deep (0.5–5 kbar, equivalent to ∼2–18 km crustal depth) decompression degassing of basaltic intrusions in Iceland results in CO2 and S fluxes of 330–5060 and 6–210 kt/yr, respectively, which is sufficient to account for the estimated CO2 flux of Icelandic VHSs (3365–6730 kt/yr), but not the VHS S flux (220–440 kt/yr). Secondary, crystallization-driven degassing from maturing intrusions and leaching of crustal rocks are suggested as additional sources of S. Only a minor proportion of the mantle flux of Cl is channeled via VHSs whereas the H2O flux remains poorly constrained, because magmatic signals in Icelandic VHSs are masked by a dominant shallow groundwater component of meteoric water origin. These results suggest that the bulk of the mantle CO2 and S flux to the atmosphere in Iceland is supplied by intrusive, not eruptive magmatism, and is largely vented via hydrothermal fields.
Highlights
• Subcrustal earthquakes detected beneath Fogo volcano, Cape Verde.
• At the focal depth of 40 km temperatures are likely too high for brittle failure.
• The earthquakes may originate from magma injection into a deep subcrustal reservoir.
• This observation indicates a distinct magma supply system of Fogo volcano.
Abstract
Fogo volcano belongs to the Cape Verde hotspot and its most recent eruption occurred from November 2014 to February 2015. From January to December 2016 we operated a temporary seismic network and array on Fogo and were able to locate 289 earthquakes in total. Array analysis shows that most of the events occur within the crust at distances >25 km near the neighboring island of Brava. However, on 15th August 2016 the network recorded an isolated cluster of >20 earthquakes, 13 of which could be located beneath the southern part of Fogo. The differences between S- and P-wave arrival times at steep incidence clearly indicate focal depths between approximately 38 and 44 km whereas receiver-function analyses place the Moho discontinuity at depths between 11 and 14 km. Thus, the earthquakes are located well within the upper mantle directly beneath Fogo. In view of the elevated upper-mantle temperatures within a hotspot regime, we propose that fracturing induced by magmatic injection is the most likely cause for the observed deep earthquakes.
Highlights
• Full automatized analysis of teleseismic XKS shear wave splitting.
• Rapid analysis of large seismological data sets.
• Automated window selection and quality classification.
• Application to the USArray Transportable Array including expansion to Alaska.
• Improved statistical evidence and objectivity of derived effective splitting.
Abstract
Recent technological advances have led to community wide use of large-scale seismic experiments which produce seismic data on previously impossible scales. Standard processing procedures thus require automatization to facilitate a fast and objective analysis of the data. Among these, XKS-splitting is an important tool to derive first insights into the Earth's deformation regimes at depth by studying seismic anisotropy. Most often, shear-wave splitting is interpreted to represent crystallographic preferred orientation (CPO) of mantle minerals like olivine as dominating feature and can thus be used as a proxy of mantle flow processes. Here, we introduce an addition to the MATLAB®-based SplitRacer tool box (Reiss and Rümpker 2017) which automatizes the entire XKS-splitting procedure. This is achieved by the automatization of 1) choosing a time window based on spectral analyses and 2) categorization of results based on three different XKS-splitting methods (energy minimization, rotation correlation and splitting intensity). This provides effective and objective results for splitting as well as null-measurement results. This extension allows to use SplitRacer without a graphical interface and introduces a bootstrapping statistics as error estimate of the single layer joint splitting method. The procedures are designed to allow a fast and more objective analysis of a vast amount of data, as produced by recent seismic deployments (e.g. USArray, AlpArray). We test this automatization by applying the analysis to the USArray data set, which has approximately 1900 stations with between two to fifteen years of data. We can reproduce the general pattern of the results from former studies with the more objective automatic analysis. Based on a joint-splitting approach, we approximate the splitting effect at individual stations by a single anisotropic layer. As we include null-measurements as well as a larger data set as previous studies, we can provide improved statistical evidence for these effective splitting parameters.
Highlights
• We show the first observations of seismo-acoustic tremor at Oldoinyo Lengai, the world's only active carbonatite volcano.
• We observe significant changes in seismic and acoustic tremor properties and their correlation in one year of data collection.
• Using satellite-based thermal data, we identify different volcanic processes (degassing, lava pond dynamics and spattering).
Abstract
We analyze volcanic tremor from Oldoinyo Lengai, Tanzania, which is currently the only active volcano on Earth producing carbonatitic lavas. Here, we use data from the recent SEISVOL deployment and focus on a co-located seismic and infrasound station about 200 m below the summit. We show the very first observations of seismo-acoustic tremor caused by carbonatitic eruptions. This seismo-acoustic tremor is highly variable throughout the ∼one year of data which we characterize by analyzing its seismic amplitude, duration, recurrence, dominant seismic frequency and harmonics. Frequency gliding occurs frequently and over short (minutes to hours) to long time scales (hours to days) and likely reflects different time-dependent mechanisms, such as evenly-spaced repeating events with a change in inter-event times, crater dynamics that alter resonators, and dike intrusions. Seismic and acoustic wavefields correlate well for stronger eruptive sequences but are only partially coherent which suggests that high-frequency seismic tremor (up to 25 Hz) may be caused by the low viscosity of the carbonatitic melt and not by ground-coupled airwaves. In addition, the comparison between seismic-acoustic and satellite InfraRed thermal data allows us to infer different volcanic activity styles which partially alternate throughout the year: intrusive activity and the construction of hornitos, degassing, activity from a lava pond, and varying styles of extrusive activity, in particular spattering. Our study provides important insights into the eruption dynamics of this peculiar volcano which suggests shallow melt storage within the crater floor.
The metasomatised continental mantle may play a key role in the generation of some ore deposits, in particular mineral systems enriched in platinum-group elements (PGE) and Au. The cratonic lithosphere is the longest-lived potential source for these elements, but the processes that facilitate their pre-concentration in the mantle and their later remobilisation to the crust are not yet well-established. Here, we report new results on the petrography, major-element, and siderophile- and chalcophile-element composition of native Ni, base metal sulphides (BMS), and spinels in a suite of well-characterised, highly metasomatised and weakly serpentinised peridotite xenoliths from the Bultfontein kimberlite in the Kaapvaal Craton, and integrate these data with published analyses. Pentlandite in polymict breccias (failed kimberlite intrusions at mantle depth) has lower trace-element contents (e.g., median total PGE 0.72 ppm) than pentlandite in phlogopite peridotites and Mica-Amphibole-Rutile-Ilmenite-Diopside (MARID) rocks (median 1.6 ppm). Spinel is an insignificant host for all elements except Zn, and BMS and native Ni account for typically <25% of the bulk-rock PGE and Au. High bulk-rock Te/S suggest a role for PGE-bearing tellurides, which, along with other compounds of metasomatic origin, may host the missing As, Ag, Cd, Sb, Te and, in part, Bi that are unaccounted for by the main assemblage.
The close spatial relationship between BMS and metasomatic minerals (e.g., phlogopite, ilmenite) indicates that the lithospheric mantle beneath Bultfontein was resulphidised by metasomatism after initial melt depletion during stabilisation of the cratonic lithosphere. Newly-formed BMS are markedly PGE-poor, as total PGE contents are <4.2 ppm in pentlandite from seven samples, compared to >26 ppm in BMS in other peridotite xenoliths from the Kaapvaal craton. This represents a strong dilution of the original PGE abundances at the mineral scale, perhaps starting from precursor PGE alloy and small volumes of residual BMS. The latter may have been the precursor to native Ni, which occurs in an unusual Ni-enriched zone in a harzburgite and displays strongly variable, but overall high PGE abundances (up to 81 ppm). In strongly metasomatised peridotites, Au is enriched relative to Pd, and was probably added along with S. A combination of net introduction of S, Au +/− PGE from the asthenosphere and intra-lithospheric redistribution, in part sourced from subducted materials, during metasomatic events may have led to sulphide precipitation at ~80–120 km beneath Bultfontein. This process locally enhanced the metallogenic fertility of this lithospheric reservoir. Further mobilisation of the metal budget stored in these S-rich domains and upwards transport into the crust may require interaction with sulphide-undersaturated melts that can dissolve sulphides along with the metals they store.
We investigate the applicability of the well-known multilevel Monte Carlo (MLMC) method to the class of density-driven flow problems, in particular the problem of salinisation of coastal aquifers. As a test case, we solve the uncertain Henry saltwater intrusion problem. Unknown porosity, permeability and recharge parameters are modelled by using random fields. The classical deterministic Henry problem is non-linear and time-dependent, and can easily take several hours of computing time. Uncertain settings require the solution of multiple realisations of the deterministic problem, and the total computational cost increases drastically. Instead of computing of hundreds random realisations, typically the mean value and the variance are computed. The standard methods such as the Monte Carlo or surrogate-based methods are a good choice, but they compute all stochastic realisations on the same, often, very fine mesh. They also do not balance the stochastic and discretisation errors. These facts motivated us to apply the MLMC method. We demonstrate that by solving the Henry problem on multi-level spatial and temporal meshes, the MLMC method reduces the overall computational and storage costs. To reduce the computing cost further, parallelization is performed in both physical and stochastic spaces. To solve each deterministic scenario, we run the parallel multigrid solver ug4 in a black-box fashion.
Reconstructing Oligocene-Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth’s surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps, however, remain scarce. Here we present stable and clumped isotope geochemistry 15 measurements to provide a new paleoelevation estimate for the mid-Miocene (~14.5 Ma) European Central Alps. We apply stable isotope δ-δ paleoaltimetry on near sea level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different 20 alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30 ± 5°C) yield a near sea level precipitation δ18Ow value of -5.8 ± 0.2‰ and in conjunction with the high-Alpine phyllosilicate δD record suggest that the region surrounding the SFZ attained surface elevations of >4000 m no later than the mid-Miocene. Our near sea level δ18Ow estimate is supported by paleoclimate (iGCM Echam5-wiso) modeled δ18O values, which vary between -4.2 and -7.6‰ for the Northern Alpine Foreland Basin.
Stratospheric inorganic chlorine (Cly) is predominantly released from long-lived chlorinated source gases and, to a small extent, very short-lived chlorinated substances. Cly includes the reservoir species (HCl and ClONO2) and active chlorine species (i.e., ClOx). The active chlorine species drive catalytic cycles that deplete ozone in the polar winter stratosphere. This work presents calculations of inorganic chlorine (Cly) derived from chlorinated source gas measurements on board the High Altitude and Long Range Research Aircraft (HALO) during the Southern Hemisphere Transport, Dynamic and Chemistry (SouthTRAC) campaign in austral late winter and early spring 2019. Results are compared to Cly in the Northern Hemisphere derived from measurements of the POLSTRACC-GW-LCYCLE-SALSA (PGS) campaign in the Arctic winter of 2015/2016. A scaled correlation was used for PGS data, since not all source gases were measured. Using the SouthTRAC data, Cly from a scaled correlation was compared to directly determined Cly and agreed well. An air mass classification based on in situ N2O measurements allocates the measurements to the vortex, the vortex boundary region, and midlatitudes. Although the Antarctic vortex was weakened in 2019 compared to previous years, Cly reached 1687±19 ppt at 385 K; therefore, up to around 50 % of total chlorine was found in inorganic form inside the Antarctic vortex, whereas only 15 % of total chlorine was found in inorganic form in the southern midlatitudes. In contrast, only 40 % of total chlorine was found in inorganic form in the Arctic vortex during PGS, and roughly 20 % was found in inorganic form in the northern midlatitudes. Differences inside the two vortices reach as much as 540 ppt, with more Cly in the Antarctic vortex in 2019 than in the Arctic vortex in 2016 (at comparable distance to the local tropopause). To our knowledge, this is the first comparison of inorganic chlorine within the Antarctic and Arctic polar vortices. Based on the results of these two campaigns, the differences in Cly inside the two vortices are substantial and larger than the inter-annual variations previously reported for the Antarctic.
Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is α-pinene, which upon oxidation can form a suite of products covering a wide range of volatilities. Highly oxygenated organic molecules (HOMs) comprise a fraction of the oxidation products formed. While it is known that HOMs contribute to secondary organic aerosol (SOA) formation, including NPF, they have not been well studied in newly formed particles due to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures (−50 and −30 ∘C) and relative humidities (20 % and 60 %) relevant in the upper free troposphere. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber. The particle chemical composition was analyzed by a thermal desorption differential mobility analyzer (TD-DMA) coupled to a nitrate chemical ionization–atmospheric pressure interface–time-of-flight (CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our measurements revealed the presence of C8−10 monomers and C18−20 dimers as the major compounds in the particles (diameter up to ∼ 100 nm). Particularly, for the system with isoprene added, C5 (C5H10O5−7) and C15 compounds (C15H24O5−10) were detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene oxidation products enhance the growth of particles larger than 15 nm. Additionally, we report on the nucleation rates measured at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower J1.7 nm values, very likely due to the higher α-pinene and ozone mixing ratios used in the present study.
Reconstructing Oligocene–Miocene paleoelevation contributes to our understanding of the evolutionary history of the European Alps and sheds light on geodynamic and Earth surface processes involved in the development of Alpine topography. Despite being one of the most intensively explored mountain ranges worldwide, constraints on the elevation history of the European Alps remain scarce. Here we present stable and clumped isotope measurements to provide a new paleoelevation estimate for the mid-Miocene (∼14.5 Ma) European Central Alps. We apply stable isotope δ–δ paleoaltimetry to near-sea-level pedogenic carbonate oxygen isotope (δ18O) records from the Northern Alpine Foreland Basin (Swiss Molasse Basin) and high-Alpine phyllosilicate hydrogen isotope (δD) records from the Simplon Fault Zone (Swiss Alps). We further explore Miocene paleoclimate and paleoenvironmental conditions in the Swiss Molasse Basin through carbonate stable (δ18O, δ13C) and clumped (Δ47) isotope data from three foreland basin sections in different alluvial megafan settings (proximal, mid-fan, and distal). Combined pedogenic carbonate δ18O values and Δ47 temperatures (30±5 ∘C) yield a near-sea-level precipitation δ18Ow value of ‰ and, in conjunction with the high-Alpine phyllosilicate δD value of ‰, suggest that the region surrounding the Simplon Fault Zone attained surface elevations of >4000 m no later than the mid-Miocene. Our near-sea-level δ18Ow estimate is supported by paleoclimate (iGCM ECHAM5-wiso) modeled δ18O values, which vary between −4.2 ‰ and −7.6 ‰ for the Northern Alpine Foreland Basin.
Stratospheric inorganic chlorine (Cly) is predominantly released from long-lived chlorinated source gases and, to a small extent, very short-lived chlorinated substances. Cly includes the reservoir species (HCl and ClONO2) and active chlorine species (i.e., ClOx). The active chlorine species drive catalytic cycles that deplete ozone in the polar winter stratosphere. This work presents calculations of inorganic chlorine (Cly) derived from chlorinated source gas measurements on board the High Altitude and Long Range Research Aircraft (HALO) during the Southern Hemisphere Transport, Dynamic and Chemistry (SouthTRAC) campaign in austral late winter and early spring 2019. Results are compared to Cly in the Northern Hemisphere derived from measurements of the POLSTRACC-GW-LCYCLE-SALSA (PGS) campaign in the Arctic winter of 2015/2016. A scaled correlation was used for PGS data, since not all source gases were measured. Using the SouthTRAC data, Cly from a scaled correlation was compared to directly determined Cly and agreed well. An air mass classification based on in situ N2O measurements allocates the measurements to the vortex, the vortex boundary region, and midlatitudes. Although the Antarctic vortex was weakened in 2019 compared to previous years, Cly reached 1687±19 ppt at 385 K; therefore, up to around 50 % of total chlorine was found in inorganic form inside the Antarctic vortex, whereas only 15 % of total chlorine was found in inorganic form in the southern midlatitudes. In contrast, only 40 % of total chlorine was found in inorganic form in the Arctic vortex during PGS, and roughly 20 % was found in inorganic form in the northern midlatitudes. Differences inside the two vortices reach as much as 540 ppt, with more Cly in the Antarctic vortex in 2019 than in the Arctic vortex in 2016 (at comparable distance to the local tropopause). To our knowledge, this is the first comparison of inorganic chlorine within the Antarctic and Arctic polar vortices. Based on the results of these two campaigns, the differences in Cly inside the two vortices are substantial and larger than the inter-annual variations previously reported for the Antarctic.
Biogenic organic precursors play an important role in atmospheric new particle formation (NPF). One of the major precursor species is α-pinene, which upon oxidation can form a suite of products covering a wide range of volatilities. Highly oxygenated organic molecules (HOMs) comprise a fraction of the oxidation products formed. While it is known that HOMs contribute to secondary organic aerosol (SOA) formation, including NPF, they have not been well studied in newly formed particles due to their very low mass concentrations. Here we present gas- and particle-phase chemical composition data from experimental studies of α-pinene oxidation, including in the presence of isoprene, at temperatures (−50 and −30 ∘C) and relative humidities (20 % and 60 %) relevant in the upper free troposphere. The measurements took place at the CERN Cosmics Leaving Outdoor Droplets (CLOUD) chamber. The particle chemical composition was analyzed by a thermal desorption differential mobility analyzer (TD-DMA) coupled to a nitrate chemical ionization–atmospheric pressure interface–time-of-flight (CI-APi-TOF) mass spectrometer. CI-APi-TOF was used for particle- and gas-phase measurements, applying the same ionization and detection scheme. Our measurements revealed the presence of C8−10 monomers and C18−20 dimers as the major compounds in the particles (diameter up to ∼ 100 nm). Particularly, for the system with isoprene added, C5 (C5H10O5−7) and C15 compounds (C15H24O5−10) were detected. This observation is consistent with the previously observed formation of such compounds in the gas phase. However, although the C5 and C15 compounds do not easily nucleate, our measurements indicate that they can still contribute to the particle growth at free tropospheric conditions. For the experiments reported here, most likely isoprene oxidation products enhance the growth of particles larger than 15 nm. Additionally, we report on the nucleation rates measured at 1.7 nm (J1.7 nm) and compared with previous studies, we found lower J1.7 nm values, very likely due to the higher α-pinene and ozone mixing ratios used in the present study.
Although global- and catchment-scale hydrological models are often shown to accurately simulate long-term runoff time-series, far less is known about their suitability for capturing hydrological extremes, such as droughts. Here we evaluated simulations of hydrological droughts from nine catchment scale hydrological models (CHMs) and eight global scale hydrological models (GHMs) for eight large catchments: Upper Amazon, Lena, Upper Mississippi, Upper Niger, Rhine, Tagus, Upper Yangtze and Upper Yellow. The simulations were conducted within the framework of phase 2a of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP2a). We evaluated the ability of the CHMs, GHMs and their respective ensemble means (Ens-CHM and Ens-GHM) to simulate observed hydrological droughts of at least one month duration, over 31 years (1971–2001). Hydrological drought events were identified from runoff-deficits and the Standardised Runoff Index (SRI). In all catchments, the CHMs performed relatively better than the GHMs, for simulating monthly runoff-deficits. The number of drought events identified under different drought categories (i.e. SRI values of -1 to -1.49, -1.5 to -1.99, and ≤-2) varied significantly between models. All the models, as well as the two ensemble means, have limited abilities to accurately simulate drought events in all eight catchments, in terms of their occurrence and magnitude. Overall, there are opportunities to improve both CHMs and GHMs for better characterisation of hydrological droughts.
Lightning climate change projections show large uncertainties caused by limited empirical knowledge and strong assumptions inherent to coarse-grid climate modeling. This study addresses the latter issue by implementing and applying the lightning potential index parameterization (LPI) into a fine-grid convection-permitting regional climate model (CPM). This setup takes advantage of the explicit representation of deep convection in CPMs and allows for process-oriented LPI inputs such as vertical velocity within convective cells and coexistence of microphysical hydrometeor types, which are known to contribute to charge separation mechanisms. The LPI output is compared to output from a simpler flash rate parameterization, namely the CAPE × PREC parameterization, applied in a non-CPM on a coarser grid. The LPI’s implementation into the regional climate model COSMO-CLM successfully reproduces the observed lightning climatology, including its latitudinal gradient, its daily and hourly probability distributions, and its diurnal and annual cycles. Besides, the simulated temperature dependence of lightning reflects the observed dependency. The LPI outperforms the CAPE × PREC parameterization in all applied diagnostics. Based on this satisfactory evaluation, we used the LPI to a climate change projection under the RCP8.5 scenario. For the domain under investigation centered over Germany, the LPI projects a decrease of 4.8% in flash rate by the end of the century, in opposition to a projected increase of 17.4% as projected using the CAPE × PREC parameterization. The future decrease of LPI occurs mostly during the summer afternoons and is related to (i) a change in convection occurrence and (ii) changes in the microphysical mixing. The two parameterizations differ because of different convection occurrences in the CPM and non-CPM and because of changes in the microphysical mixing, which is only represented in the LPI lightning parameterization.
Global analysis of halogenated trace gases in the UTLS: from long-lived to short-lived substances
(2023)
In this dissertation, the distribution of chlorinated and brominated substances in the upper troposphere and lower stratosphere is investigated. These substances contribute significantly to the catalytic decomposition of ozone and are involved in the recurrent formation of the polar ozone hole in the Antarctic winter and spring. The Montreal Protocol, a multilateral environmental treaty to protect the ozone layer, has successfully reduced emissions of long-lived chlorine- and bromine-containing substances. Short-lived chlorinated and brominated substances, some of which are natural and anthropogenic in origin, are not regulated by the Montreal Protocol and it can be assumed that their relative contribution to the stratospheric halogen budget will increase, while the contribution of long-lived compounds will steadily decrease. The distribution of long- and short-lived halogenated substances are part of current research. For the upper troposphere and lower stratosphere, the very short-lived substances are particularly important. The lower stratosphere needs special investigation in this respect, since its composition is influenced by different transport processes. The influences on ozone trends in the lower stratosphere are subject to great uncertainties. Especially in the Southern Hemisphere, the number of observations is very limited.
In this work, the GhOST (Gas chromatograph for Observational Studies using Tracers) instrument was used during the SouthTRAC measurement campaign on the German HALO (High Altitude and LOng range) research aircraft, providing observations of halogenated hydrocarbons in Antarctic late winter to early spring 2019, a generally poorly sampled region. The polar vortex was, compared to previous years, significantly weaker and shifted towards the eastern South Pacific and South America. From the airborne measurements of chlorinated source gases, inorganic chlorine (the sum of active chlorine and reservoir gases; Cly) could be inferred with the result that Cly within the vortex increased up to 1687 ± 19 ppt at 385 K potential temperature, accounting for about 50 % of the total chlorine within the vortex and only 15 % of the total chlorine in the southern mid-latitudes. A comparison with the Northern Hemisphere could be made using the PGS measurement campaign in the Arctic winter 2015/2016. Under comparable conditions (season and distance from the tropopause), only 40 % of the total chlorine was in the inorganic form within the Arctic polar vortex and about 20 % was found in the mid-latitudes of the Northern Hemisphere. In addition, about 540 ppt more Cly was present in the Antarctic vortex than in the Arctic vortex, exceeding the annual variations previously reported for Antarctica.
The mean age of air plays an essential role in the derivation of Cly via the organic source gases, as was done in this work. A new method for determining the mean age of air from observational data has been introduced that accounts for extra-tropical input to the stratosphere in addition to tropical input. This new method was compared with the previously used method, which considered only the tropical input. The new method shows more realistic values especially near the tropopause. On average, the air of the lower stratosphere in the Northern Hemisphere was older than in the Southern Hemisphere by about 0.5 ± 0.3 years. About 65 K above the tropopause, the pattern changed with older air in the mid-latitudes of the Northern Hemisphere, but older air in high latitudes of the Southern Hemisphere, which implies differences in the strength and isolation of the respective polar vortex as well as the wave forcing in the shallow branch of the Brewer-Dobson circulation of the respective hemisphere. This is in good agreement with the distribution of Cly. The difference in the lower stratosphere was not clearly evident with the old method and it can be assumed that investigations of the differences in Cly of Northern and Southern Hemisphere will benefit from the new method.
Finally, the global and seasonal distribution of the two most important representatives of the short-lived brominated substances, CH2Br2 and CHBr3, was investigated. For this purpose, two additional HALO measurement campaigns have been used, the 2012 TACTS measurement campaign and the 2017 WISE measurement campaign, as well as the HIAPER Pole-to-Pole Observations (HIPPO) and Atmospheric Tomography (ATom) measurement campaigns. Observations of CH2Br2 show a pronounced seasonality in the free and upper troposphere of both hemispheres with slightly larger values in the Northern Hemisphere. CHBr3, on the other hand, shows a generally higher variability and lower seasonality with larger mixing ratios at mid and high latitudes in the northern hemispheric winter and autumn. A comparison of the lower stratosphere is limited to autumn and spring of both hemispheres due to the limited data basis of the observations. The distributions in each spring are similar (less than 0.1 ppt differences for e.g., CH2Br2). In hemispheric autumn, larger differences are evident with substantially smaller mixing ratios in the southern hemispheric lower stratosphere. This suggests that the transport processes of the two hemispheres may be different and implies that the input of tropospheric air (flushing) to the Northern Hemisphere lowest stratosphere is more efficient than in the Southern Hemisphere. Vertical profiles of CH2Br2 and CHBr3 in the mid-latitudes of both hemispheres and resulting vertical gradients support this conjecture. However, the Southern Hemisphere data set is insufficient to quantify this difference and further measurements are needed.
Semi-arid African ecosystems influence trends and variability in global terrestrial carbon dynamics. However, there are uncertainties in potential effects of future climates for semi-arid ecosystems, especially for niche ecosystems. At the same time, African ecosystems provide the livelihoods and ecosystem services for around 1.4 billion people. Future population growth and associated changes in land use pose a challenge for the protection of African biodiversity. Therefore, this work focussed on future impacts of climate change on African ecosystems and carbon dynamics and also for African protected areas (PAs), where they may cooccur with other global change factors. Another focus was on uncertainties associated with future projections and with modelling the Nama Karoo, as an example of a semi-arid niche ecosystem. Dynamic vegetation models (DVMs) were the main research tool.
In Chapter 2, we analysed climate change impacts on African ecosystems and carbon pools until the end of the 21st century and associated uncertainties based on an ensemble of vegetation simulations with the DVM adaptive dynamic vegetation model (aDGVM). We investigated the impact of increased atmospheric CO2 concentrations and two climate change scenarios (medium (RCP4.5) and high emissions (RCP8.5); RCP - representative concentration pathway) on vegetation changes. Differences in the simulated vegetation were primarily driven by assumptions about the influence of CO2 on plants. Elevated CO2 concentrations led to increased total aboveground vegetation biomass and shrub encroachment into grasslands and savannas for both climate scenarios. In simulations without the direct influence of CO2 on plants, there was hardly any shrub encroachment and vegetation biomass decreased or varied between a slight decrease in some cases and a slight increase in others. Based on these results, biome changes due to climate change are likely in Africa in the future. Due to the large uncertainties in future projections, strategies to adapt to climate change must be flexible.
The simulated vegetation in Chapter 2 represented potential, natural vegetation and is particularly suitable to investigate PAs. However, PAs do not exist isolated from their environment and social developments. In Chapter 3, the vegetation projections with CO2 effect from Chapter 2 were combined with projections for population density and land use. Except for many PAs in North Africa, most PAs were adversely affected by at least one of the three drivers by the end of the 21st century in both investigated scenarios ("middle-of-the-road" and "fossil-fuelled development"). Cooccurrence of the drivers varied by region and scenario for PAs. Both scenarios implied increasing challenges for the conservation of African biodiversity in PAs. The impact of climate change on vegetation is likely to be exacerbated by socio-economic change for most African PAs. Strong mitigation of future climate change together with equitable societal development may facilitate successful ecosystem conservation.
The simulations in Chapters 2 and 3 showed large-scale patterns of vegetation change, but their low resolution makes them unsuitable for local analyses. In Chapter 4, the challenges of simulating smaller scale, semi-arid ecosystems and their carbon cycle were analysed for the Nama Karoo with the aDGVM2 and its shrub module. The aDGVM2 is based on the aDGVM, but represents plants more flexibly. In all tested aDGVM2 configurations, the carbon fluxes improved compared to initial simulations but still overestimated them. The measured morphology of the dwarf shrubs and soil water dynamics were not reproduced in aDGVM2. Semi-arid soil water dynamics and coping strategies of semi-arid dwarf shrubs under drought stress are not adequately implemented in the aDGVM2. Further field research on semi-arid water and carbon dynamics of vegetation is necessary to parameterise the aDGVM2 for dwarf shrubs. If these challenges are overcome, DVMs can be a powerful tool for much-needed research on the impacts of climate change on the Nama Karoo.
The analyses have shown that climate change under medium to high emission scenarios is likely to lead to large-scale changes in ecosystems and the carbon balance in Africa. Because lower emissions scenarios come with less uncertainty, climate change adaptation strategies likely need to be less complex or extensive if climate change is minimised. For African PAs, the challenges of climate change may be exacerbated by socio-economic factors to a regionally varying extent. This research suggests that successful ecosystem conservation depends on climate change mitigation measures and ensuring equitable, sustainable development. The shown uncertainties, e.g., in the implementation of the CO2 effect on plants or vegetation dynamics in more niche ecosystems, help to focus future research efforts and increase our understanding of the range of plausible futures we may need to adapt to.
First-principles modeling techniques offer the ability to simulate a wide range of systems under different physical conditions, such as temperature, pressure, and composition, without relying on empirical knowledge. Density functional theory (DFT), a quantum mechanical method, has become an exceptionally successful framework for materials science modeling. Employing DFT makes it possible to gain valuable insights into the fundamental state of a system, enabling the reliable determination of equilibrium crystal structures. Over time, DFT has become an essential tool that can be incorporated into various schemes for predicting the properties of a material related to its structure, insulating/metallic behavior, magnetism, and optics. DFT is regularly applied in numerous fields, spanning from fundamental subjects in condensed matter physics to the study of large-scale phenomena in geosciences. In the latter, the effectiveness of DFT stems from its ability to simulate the properties found on the Earth, other planets, and meteorites, which may pose challenges for their direct study or laboratory investigation.
In this thesis, a comprehensive examination of a family of monosulfides and a perovskite heterostructure was conducted. These materials are relevant for their potential applications in technology, energy harvesting, and in the case of monosulfides, their speculated abundance on the planet Mercury.
Firstly, a DFT approach was used to analyze two non-magnetic monosulfides, CaS and MgS. We determined their structural properties and then focused on the modeling of their reflectivity in the infrared region. The calculation of the reflectivity considered both harmonic and anharmonic contributions. In the harmonic limit, the non-analytic correction was employed to accurately determine the LO/TO splitting, which is necessary to delimit the retstrahlend band, that is, the maximum of the reflectivity. The anharmonic effects given by up to three-phonon and isotopic scatterings, which were included using perturbation theory, primarily smeared the reflectivity spectra edges in the high-wave region.
Secondly, four polymorphs of MnS were studied using a combination of first-principles methods to simulate their antiferromagnetic (AFM) and paramagnetic (PM) states. The integration of DFT+$U$ with special quasirandom structures (SQS) supercells, and occupation matrix control techniques was crucial for achieving convergence, structural optimization accuracy, and obtaining finite energy band gaps and local magnetic moments in the PM phases. The addition of the Hubbard $U$ correction was necessary to treat the highly-correlated Mn $d$-electrons. The success of our approach was clear based on our electronic structure predictions for the PM rock-salt B1-MnS polymorph. Experimentally this phase has been observed to be an insulator, but multiple \emph{ab initio} works resulted previously in metallic behavior. Our computations, on the other hand, predicted insulating and magnetic properties that compare well with available measurements. Additionally, the pressure-field stability of the four MnS polymorphs was studied. In the case of the PM phases, B1-MnS was identified to be the most stable up to about 21 GPa, then transforming into the B31-MnS polymorph. This finding was in close agreement with high-pressure experiments reporting a similar phase transformation. The optical properties of B1-, B4-, and B31-MnS were also simulated. The SQS technique was used to obtain soft-mode-free phonon band structures within the harmonic approximation. Then, the anharmonic effects were included, and the reflectivity was calculated for B1-MnS and B4-MnS. In both cases, a good agreement for the LO/TO splitting was achieved in comparison to experimental results.
Lastly, the oxygen-deficient heterostructure of LaAlO$_{3-\delta}$ /SrTiO$_{3-\delta}$ was investigated also employing DFT+$U$, with a particular emphasis on the potential impact of vacancy clustering at the interface. Six distinct configurations of pairs of vacancies were studied and their energies were compared to find the most stable one. The orbital reconstruction of Ti orbitals was also examined based on their location with respect to the vacancies and the local magnetic moments were calculated. The final results showed that linearly arranged vacancies located opposite to Ti ions give the most energetically stable configuration.
Climatology of morphology and cloud-radiative properties of marine low-level mixed-phase clouds
(2023)
Marine stratocumuli cover about 40 - 60% of the ocean surface. They self-organize into different morphological regimes. The two organized cellular regimes are called open and closed mesoscale-cellular convective (MCC) clouds. In mid-to-high latitudes, open and closed cells are the two most frequent types of MCC clouds. In particular, many MCC clouds consist of a mixture of vapor, liquid droplets, and ice particles, referred to as mixed-phase clouds (MPCs). Even for the same cloud fraction, the albedo of open cells is, on average, lower than that of closed MCC clouds. Cloud phase and morphology individually influence the cloud radiative effect. Thus, this thesis investigates the relationships between the cloud phase, MCC organization, cell size, and differences regarding the cloud-radiative effect.
This thesis focuses on space-borne retrievals to achieve extensive temporal and spatial coverage. The liDAR-raDAR (DARDAR) version 2 product collocates two active and one passive satellite: CloudSat, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and Moderate Resolution Imaging Spectroradiometer (MODIS). The cloud phase of DARDAR is vertically integrated to establish a single cloud phase at each data point. The MCC classification data set based on the liquid water path (LWP) of MODIS scenes is collocated with the DARDAR product to determine the MCC organization. Cell-size statistics of both MCC clouds are obtained using a marker-based image segmentation method on MODIS reflectance scenes. In addition, based on MODIS reflectance scenes, a convolutional neural network (CNN) is developed to classify open and closed MCC scenes to avoid missing mature MPCs with a low LWP.
The first part of this thesis explores the relationships between cloud phase, morphology, and cloud albedo in the Southern Ocean (SO). At a given cloud-top temperature (CTT), seasonal changes in the mixed-phase fraction, defined as the number of MPCs divided by the sum of MPC and supercooled liquid cloud (SLC) pixels, are stronger than the morphological changes. Therefore, external factors seem to influence these changes instead of morphology. The dependence of cloud phase on cloud-top height (CTH) is more substantial than on CTT in clouds with CTHs below 2.5 km. The previously observed acceleration of closed-to-open transition in MPCs, known as preconditioning, is not the primary driver of climatological cloud morphology statistics in the SO. The morphological differences in cloud albedo are more pronounced in SLCs than in MPCs. This change in albedo alters the cloud radiative effect in the SO by 21Wm−2 to 39Wm−2 depending onseason and cloud phase.
Open and closed MCC clouds exhibit larger equivalent cell diameters in the MPCs than in SLCs in austral summer, whereas, in austral winter, the SLCs are larger. The cell’s aspect ratio accounts for varying CTHs. Closed cells have smaller aspect ratios than open cells, so their cell diameter is smaller, independent of CTH. While the seasonal differences in closed cells are due to changes in CTH, the seasonal aspect ratio differences in open cells are mainly caused by MPCs. With increasing aspect ratios, the cloud albedo decreases in both open and closed MCC clouds, with the most substantial decrease in open MPCs clouds. This leads to cloud-radiative changes of 60 - 75Wm−2 in the SO, depending on cloud phase and aspect ratio.
The established CNN exhibits a good accuracy of 80.6%, with even higher accuracies in the Open (85.5%) and Closed (87.3%) categories. The global MCC climatology based on the CNN generally agrees well with previous MCC distributions. The most notable difference occurs in the Northern Hemisphere (NH) in boreal winter, with a higher occurrence frequency of closed and open MCC clouds. This might indicate missing MPCs in previous studies based on the LWP and some restricted to warm cloud scenes. Thus, the developed CNN seems to better represent the different morphologies in MPCs than in previous classifications.
In conclusion, this thesis shows that understanding the dependencies of cloud phase, cloud morphology, and cell size is important to enhance predictions of the cloud-radiative effect and thus, it is important to evaluate how cloud phase, cloud morphology, and cellsize change in a warming climate.
Due to massive energetic investments in woody support structures, trees are subject to unique physiological, mechanical, and ecological pressures not experienced by herbaceous plants. Despite a wealth of studies exploring trait relationships across the entire plant kingdom, the dominant traits underpinning these unique aspects of tree form and function remain unclear. Here, by considering 18 functional traits, encompassing leaf, seed, bark, wood, crown, and root characteristics, we quantify the multidimensional relationships in tree trait expression. We find that nearly half of trait variation is captured by two axes: one reflecting leaf economics, the other reflecting tree size and competition for light. Yet these orthogonal axes reveal strong environmental convergence, exhibiting correlated responses to temperature, moisture, and elevation. By subsequently exploring multidimensional trait relationships, we show that the full dimensionality of trait space is captured by eight distinct clusters, each reflecting a unique aspect of tree form and function. Collectively, this work identifies a core set of traits needed to quantify global patterns in functional biodiversity, and it contributes to our fundamental understanding of the functioning of forests worldwide.
The Izu–Bonin–Mariana volcanic arc is situated at a convergent plate margin where subduction initiation triggered the formation of MORB-like forearc basalts as a result of decompression melting and near-trench spreading. International Ocean Discovery Program (IODP) Expedition 352 recovered samples within the forearc basalt stratigraphy that contained unusual macroscopic globular textures hosted in andesitic glass (Unit 6, Hole 1440B). It is unclear how these andesites, which are unique in a stratigraphic sequence dominated by forearc basalts, and the globular textures therein may have formed. Here, we present detailed textural evidence, major and trace element analysis, as well as B and Sr isotope compositions, to investigate the genesis of these globular andesites. Samples consist of K2O-rich basaltic globules set in a glassy groundmass of andesitic composition. Between these two textural domains a likely hydrated interface of devitrified glass occurs, which, based on textural evidence, seems to be genetically linked to the formation of the globules. The andesitic groundmass is Cl rich (ca. 3000 µg/g ), whereas globules and the interface are Cl poor (ca. 300 µg/g ). Concentrations of fluid-mobile trace elements also appear to be fractionated in that globules and show enrichments in B, K, Rb, Cs, and Tl, but not in Ba and W relative to the andesitic groundmass, whereas the interface shows depletions in the latter, but is enriched in the former. Interestingly, globules and andesitic groundmass have identical Sr isotopic composition within analytical uncertainty ( 87Sr∕86Sr of 0.70580 ± 10 ), indicating that they likely formed from the same source. However, globules show high δ11 B (ca. + 7 ‰ ), whereas their host andesites are isotopically lighter (ca. – 1 ‰ ), potentially indicating that whatever process led to their formation either introduced heavier B isotopes to the globules, or induced stable isotope fractionation of B between globules and their groundmass. Based on the bulk of the textural information and geochemical data obtained from these samples, we conclude that these andesites likely formed as a result of the assimilation of shallowly altered oceanic crust (AOC) during forearc basaltic magmatism. Assimilation likely introduced radiogenic Sr, as well as heavier B isotopes to comparatively unradiogenic and low δ11B forearc basalt parental magmas (average 87Sr∕86Sr of 0.703284). Moreover, the globular textures are consistent with their formation being the result of fluid-melt immiscibility that was potentially induced by the rapid release of water from assimilated AOC whose escape likely formed the interface. If the globular textures present in these samples are indeed the result of fluid-melt immiscibility, then this process led to significant trace element and stable isotope fractionation. The textures and chemical compositions of the globules highlight the need for future experimental studies aimed at investigating the exsolution process with respect to potential trace element and isotopic fractionation in arc magmas that have perhaps not been previously considered.
Knowledge about the initial tectonic and depositional dynamics, as well as the influence of early rifting on climate and environmental evolution remains speculative to a large extent, because sediments are usually deeply buried. Within the East African Rift System, inversion tectonics uplifted a few of these successions to the surface hence presenting rare windows into the pre-rift depositional history. One such example, an exceptional 700 m long and up to 60 m high fresh road cut provided the opportunity to study in detail initial rift successions of the southern Albertine Rift (Western Uganda). This focusses on the basal and poorly known Middle to Late Miocene in order to unravel the climatic, environmental, hydrological and tectonic evolution of the initial Albertine Rift. A large and robust multi-proxy dataset was gathered comprising 169 m of stratigraphic thickness, which spans from 14.5 to 4.9 Ma according to a revised lithostratigraphic model. Fieldwork comprised logging of the sedimentary record, spectral gamma ray, magnetic susceptibility and 2D wall mapping with photomosaics. Additionally, the sections were sampled for bulk mineral and clay mineral analysis. The succession exposes a suite of lithofacies and architectural elements detailing the evolution of a fluvio-lacustrine system. Five depositional environments were identified which show an overall back-stepping trend from an alluvial plain to a delta plain and finally palustrine/shallow lacustrine conditions. Mesoscale base-level cycles, preservation potential of architectural elements, and stacking pattern exhibit limited accommodation space. However, it increases over time. This overall trend indicates increasing tectonic subsidence, which can be explained by flexural downwarp within the pre-rift phase and in the upper part grading into fault-controlled crustal extension of the syn-rift phase, which more and more disrupted a large-scale river system. From the Middle Miocene up to the early Pliocene, this study revealed that palaeoclimate trends become marked by increasing and more fluctuating Th concentrations, loss of feldspar, intercalated lenses of hydroxosulphate minerals, and a shift from smectite-dominated to kaolinite-dominated clays. These signals are all interpreted as detrital except for the hydroxosulphates, and they mirror the increasing intensity of chemical weathering and stripping of soils in the catchment. A trend towards increasing humidity is supported by an increase in lacustrine sediment facies and a lake-level rise. Nevertheless, intercalation of hydroxosulphate, ferricretes and pedogenised horizons prove ongoing seasonality and dry intervals. Finally, based on a revised stratigraphic model a sequence stratigraphic correlation of the outcrop's depositional cycles with basin-scale cycles is presented. According to these cycles, transition from the pre-rift to the syn-rift stage is marked by an unconformity and a tectonic pulse in the latest Miocene. However, the response of fluvial supply, the depositional system as well as climate conditions are less punctuated and characterised by gradual trends and temporal delays. The long pre-rift phase (ca 10 Myr) and the gradual transition to the syn-rift phase is in accordance with the active rifting model, which is based on thermal thinning of the lithosphere by asthenospheric upwelling.
Herein, the high-pressure/high-temperature synthesis (11 GPa, 650 °C) of Tb3B10O17(OH)5 in a modified Walker-type multianvil device is presented. The structure of this rare-earth borate was determined by single-crystal X-ray diffraction methods and was found to crystallize orthorhombically in the space group Pmn21 (no. 31) with the unit cell parameters a = 16.2527(4), b = 4.4373(1), and c = 8.8174(2) Å. The new compound was further characterized using infrared spectroscopy, energy-dispersive X-ray spectroscopy, second harmonic generation (SHG) measurements, and temperature-dependent X-ray powder diffraction. Tb3B10O17(OH)5 decomposes to β-Tb(BO2)3 at temperatures higher than 460 °C. With increasing temperatures, the formation of μ-TbBO3 was observed, which transforms to π-TbBO3 upon cooling.
High-pressure/high-temperature synthesis of the new boron-rich terbium hydroxyborate Tb3B12O19(OH)7
(2023)
Monoclinic Tb3B12O19(OH)7 was obtained by multianvil high-pressure/high-temperature syntheses at 6 GPa and 650 °C. The crystal structure was investigated by single-crystal X-ray diffraction methods and space group C2 (no. 5) with the unit cell parameters a = 24.2299(5) Å, b = 4.4667(1) Å, c = 7.0964(2) Å, β = 94.58(1)°, and two formula units per cell were revealed. Powder X-ray diffraction, infrared spectroscopy and the investigation of its second harmonic generation properties support the proposed structural model.
In this dissertation, different aspects of turbulent transport and thermally driven flows over complex terrain are investigated. Two publications concentrate on the vertical heat and moisture exchange in the convective boundary layer over mountainous terrain. To study this, Large-Eddy Simulation (LES) is used. Both turbulent and advective transport mechanisms are evaluated over the simple orography of a quasi-two-dimensional, periodic valley with prescribed surface fluxes. Here, terrain elevation varies along only one of the horizontal coordinate axes. Even a relatively shallow orography, possibly unresolved in existing numerical weather prediction models, modifies the domain-averaged moisture and temperature profiles. For the analysis, the flow is decomposed into a local turbulent part, a local mean circulation, and a large-scale part. An analysis of the turbulent kinetic energy and turbulent heat and moisture flux budgets shows that the thermal circulation significantly contributes to the vertical transport. It is found that thermal upslope winds are important for the moisture transport from the valley to the mountain tops. In total, moisture export out of the valley is mostly accomplished by the mean circulation. On the temperature distribution, which is horizontally relatively homogeneous, the thermal circulation has a weaker impact. If an upper-level wind is present, it interacts with the thermal circulation. This weakens the vertical transport of moisture and thus reduces its export out of the valley. The heat transport is less affected by the upper-level wind because of its weaker dependence on the thermal circulation. These findings were corroborated in a more realistic experiment simulating the full diurnal cycle using radiation forcing and an interactive land surface model.
Based on these results, coherent turbulent structures in the convective boundary layer over non-flat terrain are studied in further detail. A conditional sampling method based on the concentration of a decaying passive tracer is implemented in order to identify the boundary-layer plumes objectively. Conditional sampling allows to quantify the contribution of plume structures to the vertical transport of heat and moisture. In case of the idealized valley, vertical transport by coherent structures is the dominant contribution to the turbulent components of both heat and moisture flux. It is comparable in magnitude to the advective transport by the mean slope-wind circulation, although it is more important for heat than for moisture transport. A set of less idealized simulations considers the flow over three-dimensional terrain. In this case, conditional sampling is carried out by using a simple domain-decomposition approach. We demonstrate that thermal updrafts are generally more frequent on hill tops than over the surroundings, but they are less persistent on the windward sides when large-scale winds are present in the free atmosphere.
The tools for flow decomposition and budget analysis are also applied in another idealized case with a quasi-two-dimensional valley featuring the stable boundary layer. Here, the formation of a low stratus cloud is investigated. The main driver for the cloud formation is radiative cooling due to outgoing longwave radiation. Despite a purely horizontal flow, the advection terms in the prognostic equations for heat and moisture produce vertical mixing across the upper cloud edge leading to a loss of cloud water content. However, this behavior is not due to any kind of thermally-driven circulation. Instead, this spurious mixing is caused by the diffusive error of the advection scheme in regions where the sloping surfaces of the terrain-following vertical coordinate intersect the cloud top. It is shown that the intensity of the (spurious) numerical diffusion strongly depends on the horizontal resolution, the order of advection, and the choice of the scalar advection scheme. A LES with 4 m horizontal resolution serves as a reference. For horizontal resolutions of a few hundred meters, carried out with a model setup as it is used in Numerical Weather Prediction, a strong reduction of the simulated liquid-water path is observed. In order to keep the (spurious) numerical diffusion at coarser resolutions small, at least a fifth-order advection scheme should be used. In the present case, a WENO scalar advection scheme turns out to increase the numerical diffusion along a sharp cloud edge compared to an upwind scheme. Furthermore, the choice of the vertical coordinate has a strong impact on the simulated liquid-water path over orography. With a modified definition of the terrain-following sigma coordinate, it is possible to produce cloud water where the classical sigma coordinate does not allow any cloud formation.
Local climate change risk assessments (LCCRAs) are best supported by a quantitative integration of physical hazards, exposures and vulnerabilities that includes the characterization of uncertainties. We propose to use Bayesian Networks (BNs) for this task and show how to integrate freely-available output of multiple global hydrological models (GHMs) into BNs, in order to probabilistically assess risks for water supply. Projected relative changes in hydrological variables computed by three GHMs driven by the output of four global climate models were processed using MATLAB, taking into account local information on water availability and use. A roadmap to set up BNs and apply probability distributions of risk levels under historic and future climate and water use was co-developed with experts from the Maghreb (Tunisia, Algeria, Morocco) who positively evaluated the BN application for LCCRAs. We conclude that the presented approach is suitable for application in the many LCCRAs necessary for successful adaptation to climate change world-wide.
At high pressures, autoionization – along with polymerization and metallization – is one of the responses of simple molecular systems to a rise in electron density. Nitrosonium nitrate (NO+NO3−), known for this property, has attracted a large interest in recent decades and was reported to be synthesized at high pressure and high temperature from a variety of nitrogen–oxygen precursors, such as N2O4, N2O and N2–O2 mixtures. However, its structure has not been determined unambiguously. Here, we present the first structure solution and refinement for nitrosonium nitrate on the basis of single-crystal X-ray diffraction at 7.0 and 37.0 GPa. The structure model (P21/m space group) contains the triple-bonded NO+ cation and the NO3− sp2-trigonal planar anion. Remarkably, crystal-chemical considerations and accompanying density-functional-theory calculations show that the oxygen atom of the NO+ unit is positively charged – a rare occurrence when in the presence of a less-electronegative element.
An update of the two-energy turbulence scheme is presented, the 2TE + APDF scheme. The original version of the two-energy scheme is able to successfully model shallow convection without the need of an additional parameterization for non-local fluxes. However, the performance of the two-energy scheme is worse in stratocumulus cases, where it tends to overestimate the erosion of the stable layers. We have identified the causes: the non-local stability parameter does not consider local stratification, the scheme lacks an internal parameter that could distinguish between a shallow convection regime and a stratocumulus regime, and it uses an inflexible turbulence length scale formulation. To alleviate this problem, we propose several modifications: an update of the stability parameter, a modified computation of the turbulence length scale, and the introduction of the entropy potential temperature to distinguish between a shallow convection and a stratocumulus regime. In addition, the two-energy scheme is coupled to a simplified assumed probability density function method in order to achieve a more universal representation of the cloudy regimes. The updated turbulence scheme is evaluated for several idealized cases and one selected real case in the ICOsahedral Nonhydrostatic (ICON) modeling framework. The results show that the updated scheme corrects the overmixing problem in the stratocumulus cases. The performance of the updated scheme is comparable to the operational setup, and can be thus used instead of the operational turbulence and shallow convection scheme in ICON. Additionally, the updated scheme improves the coupling with dynamics, which is beneficial for the modeling of coherent flow structures in the atmospheric boundary layer.
The accessories perovskite, pyrochlore, zirconolite, calzirtite and melanite from carbonatites and carbonate-rich foidites from the Kaiserstuhl are variously suited for the in situ determination of their U–Pb ages and Sr, Nd- and Hf-isotope ratios by LA-ICP-MS. The 143Nd/144Nd ratios may be determined precisely in all five phases, the 176Hf/177Hf ratios only in calzirtite and the 87Sr/86Sr ratios in perovskites and pyrochlores. The carbonatites and carbonate-rich foidites belong to one of the three magmatic groups that Schleicher et al. (1990) distinguished in the Kaiserstuhl on the basis of their Sr, Nd and Pb isotope ratios. Tephrites, phonolites and essexites (nepheline monzogabbros) form the second and limburgites (nepheline basanites) and olivine nephelinites the third. Our 87Sr/86Sr isotope data from the accessories overlap with the carbonatite and olivine nephelinite fields defined by Schleicher et al. (1990) but exhibit a much narrower range. These and the εNd and εHf values plot along the mantle array in the field of oceanic island basalts relatively close to mid-ocean ridge basalts. Previously reported K–Ar, Ar–Ar and fission track ages for the Kaiserstuhl lie between 16.2 and 17.8 Ma. They stem entirely from the geologically older tephrites, phonolites and essexites. No ages existed so far for the geologically younger carbonatites and carbonate-rich foidites except for one apatite fission track age (15.8 Ma). We obtained precise U–Pb ages for zirconolites and calzirtites of 15.66, respectively 15.5 Ma (± 0.1 2σ) and for pyrochlores of 15.35 ± 0.24 Ma. Only the perovskites from the Badberg soevite yielded a U–P concordia age of 14.56 ± 0.86 Ma while the perovskites from bergalites (haüyne melilitites) only gave 206Pb/238U and 208Pb/232Th ages of 15.26 ± 0.21, respectively, 15.28 ± 0.48 Ma. The main Kaiserstuhl rock types were emplaced over a time span of 1.6 Ma almost 1 million years before the carbonatites and carbonate-rich foidites. These were emplaced within only 0.32 Ma.
Living on the edge: environmental variability of a shallow late Holocene cold-water coral mound
(2022)
Similar to their tropical counterparts, cold-water corals (CWCs) are able to build large three-dimensional reef structures. These unique ecosystems are at risk due to ongoing climate change. In particular, ocean warming, ocean acidification and changes in the hydrological cycle may jeopardize the existence of CWCs. In order to predict how CWCs and their reefs or mounds will develop in the near future one important strategy is to study past fossil CWC mounds and especially shallow CWC ecosystems as they experience a greater environmental variability compared to other deep-water CWC ecosystems. We present results from a CWC mound off southern Norway. A sediment core drilled from this relatively shallow (~ 100 m) CWC mound exposes in full detail hydrographical changes during the late Holocene, which were crucial for mound build-up. We applied computed tomography, 230Th/U dating, and foraminiferal geochemical proxy reconstructions of bottom-water-temperature (Mg/Ca-based BWT), δ18O for seawater density, and the combination of both to infer salinity changes. Our results demonstrate that the CWC mound formed in the late Holocene between 4 kiloannum (ka) and 1.5 ka with an average aggradation rate of 104 cm/kiloyears (kyr), which is significantly lower than other Holocene Norwegian mounds. The reconstructed BWTMg/Ca and seawater density exhibit large variations throughout the entire period of mound formation, but are strikingly similar to modern in situ observations in the nearby Tisler Reef. We argue that BWT does not exert a primary control on CWC mound formation. Instead, strong salinity and seawater density variation throughout the entire mound sequence appears to be controlled by the interplay between the Atlantic Water (AW) inflow and the overlying, outflowing Baltic-Sea water. CWC growth and mound formation in the NE Skagerrak was supported by strong current flow, oxygen replenishment, the presence of a strong boundary layer and larval dispersal through the AW, but possibly inhibited by the influence of fresh Baltic Water during the late Holocene. Our study therefore highlights that modern shallow Norwegian CWC reefs may be particularly endangered due to changes in water-column stratification associated with increasing net precipitation caused by climate change.
We performed an experiment under long-term microgravity conditions aboard the International Space Station (ISS) to obtain information on the energetics and experimental constraints required for the formation of chondrules in the solar nebula by ’nebular lightning’. As a simplified model system, we exposed porous forsterite (Mg2 SiO4) dust particles to high-energetic arc discharges. The characterization of the samples after their return by synchrotron microtomography and scanning electron microscopy revealed that aggregates had formed, consisting of several fused Mg2SiO4 particles. The partial melting and fusing of Mg2SiO4 dust particles under microgravity conditions leads to a strong reduction of their porosity. The experimental outcomes vary strongly in their appearance from small spherical melt-droplets (∅≈90 µm) to bigger and irregularly shaped aggregates (∅≈350 µm). Our results provided new constraints with respect to energetic aspects of chondrule formation and a roadmap for future and more complex experiments on Earth and in microgravity conditions.
Several past summer floods in Central Europe were associated with so-called Vb‑cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. This study illustrates the usefulness of the parametric transfer entropy measure TE‑linear in investigating heavy Vb‑cyclone precipitation events in the Odra catchment (Poland). With the application of the TE‑linear approach, we confirm the impact of the Mediterranean Sea on precipitation intensification. Moreover, we also detect significant information exchange to Vb‑cyclone precipitation from evaporation over the European continent along the typical Vb‑cyclone pathway. Thus, the Mediterranean Sea could enhance the Vb‑cyclone precipitation by pre-moistening continental moisture source regions that contribute to precipitation downstream in the investigated catchments. Overall, the transfer entropy approach with the measure TE‑linear proved to be computationally effective and complementary to traditional methods such as Lagrangian and Eulerian diagnostics.
This work describes the development and characterization of two instruments and their data evaluation, which contributes to a better understanding of new particle formation and growth, as well as their interactions with clouds. Both instruments were characterized at the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at the European Center for Nuclear Research (CERN).
Climatic and biogeographical drivers of functional diversity in the flora of the Canary Islands
(2022)
Aim: Functional traits can help us to elucidate biogeographical and ecological processes driving assemblage structure. We analysed the functional diversity of plant species of different evolutionary origins across an island archipelago, along environmental gradients and across geological age, to assess functional aspects of island biogeographical theory.
Location: Canary Islands, Spain.
Major taxa studied: Spermatophytes.
Time period: Present day.
Methods: We collected data for four traits (plant height, leaf length, flower length and fruit length) associated with resource acquisition, competitive ability, reproduction and dispersal ability of 893 endemic, non-endemic native and alien plant species (c. 43% of the Canary Island flora) from the literature. Linking these traits to species occurrences and composition across a 500 m × 500 m grid, we calculated functional diversity for endemic, non-endemic native and alien assemblages using multidimensional functional hypervolumes and related the resulting patterns to climatic (humidity) and island biogeographical (geographical isolation, topographic complexity and geological age) gradients.
Results: Trait space of endemic and non-endemic native species overlapped considerably, and alien species added novel trait combinations, expanding the overall functional space of the Canary Islands. We found that functional diversity of endemic plant assemblages was highest in geographically isolated and humid grid cells. Functional diversity of non-endemic native assemblages was highest in less isolated and humid grid cells. In contrast, functional diversity of alien assemblages was highest in arid ecosystems. Topographic complexity and geological age had only a subordinate effect on functional diversity across floristic groups.
Main conclusions: We found that endemic and non-endemic native island species possess similar traits, whereas alien species tend to expand functional space in ecosystems where they have been introduced. The spatial distribution of the functional diversity of floristic groups is very distinct across environmental gradients, indicating that species assemblages of different evolutionary origins thrive functionally in dissimilar habitats.
In order to gain further insights into early solar system aggregation processes, we carried out an experiment on board the International Space Station, which allowed us to study the behavior of dust particles exposed to electric arc discharges under long-term microgravity. The experiment led to the formation of robust, elongated, fluffy aggregates, which were studied by scanning electron microscopy, electron backscatter diffraction, and synchrotron micro-computed tomography. The morphologies of these aggregates strongly resemble the typical shapes of fractal fluffy-type calcium-aluminum-rich inclusions (CAIs). We conclude that a small amount of melting could have supplied the required stability for such fractal structures to have survived transportation and aggregation to and compaction within planetesimals. Other aggregates produced in our experiment have a massy morphology and contain relict grains, likely resulting from the collision of grains with different degrees of melting, also observed in some natural CAIs. Some particles are surrounded by igneous rims, which remind in thickness and crystal orientation of Wark–Lovering rims; another aggregate shows similarities to disk-shaped CAIs. These results imply that a (flash-)heating event with subsequent aggregation could have been involved in the formation of different morphological CAI characteristics.
Convective rain cell properties and the resulting precipitation scaling in a warm-temperate climate
(2022)
Convective precipitation events have been shown to intensify at rates exceeding the Clausius–Clapeyron rate (CC rate) of ca. 7% K−1 under current climate conditions. In this study, we relate atmospheric variables (low-level dew point temperature, convective available potential energy, and vertical wind shear), which are regarded as ingredients for severe deep convection, to properties of convective rain cells (cell area, maximum precipitation intensity, lifetime, precipitation sum, and cell speed). The rain cell properties are obtained from a rain gauge-adjusted radar dataset in a mid-latitude region, which is characterized by a temperate climate with warm summers (Germany). Different Lagrangian cell properties scale with dew point temperature at varying rates. While the maximum precipitation intensity of cells scales consistently at the CC rate, the area and precipitation sum per cell scale at varying rates above the CC rate. We show that this super-CC scaling is caused by a covarying increase of convective available potential energy with dew point temperature. Wind shear increases the precipitation sum per cell mainly by increasing the spatial cell extent. From a Eulerian point of view, this increase is partly compensated by a higher cell velocity, which leads to Eulerian precipitation scaling rates close to and slightly above the CC rate. Thus, Eulerian scaling rates of convective precipitation are modulated by convective available potential energy and vertical wind shear, making it unlikely that present scaling rates can be applied to future climate conditions. Furthermore, we show that cells that cause heavy precipitation at fixed locations occur at low vertical wind shear and, thus, move relatively slowly compared to typical cells.
Moisture sources of heavy precipitation in Central Europe in synoptic situations with Vb-cyclones
(2022)
During the past century, several extreme summer floods in Central Europe were associated with so-called Vb-cyclones propagating from the Mediterranean Sea north-eastward to Central Europe. The processes intensifying the precipitation in synoptic situations with Vb-cyclones in the Danube, Elbe, and Odra catchments are only partially understood. Our study aims to investigate these processes with Lagrangian moisture-source diagnostics for 16 selected Vb-events. Moreover, we analyse the characteristics of typical moisture source regions during 1107 Vb-events from 1901 to 2010 based on ERA-20C reanalysis dynamically downscaled with COSMO-CLM+NEMO. We observe moisture contributions by various source regions highlighting the complex dynamical interplay of different air masses leading to moisture convergence in synoptic situations with Vb-cyclones. Overall, up to 80% of the precipitation originates from the European continent, indicating the importance of continental moisture recycling, especially within the respective river catchment. Other major moisture uptake regions are the North Sea, the Baltic Sea, the North Atlantic, and for a few events the Black Sea. Remarkably, anomalies in these oceanic source regions show no connection to precipitation amounts in synoptic situations with Vb-cyclones. In contrast, the Vb-cyclones with the highest precipitation are associated with anomalously high evaporation in the Mediterranean Sea, even though the Mediterranean Sea is only a minor moisture source region on average. Interestingly, the evaporation anomalies are not connected with sea-surface temperature but with wind-speed anomalies (Spearman’s rank correlation coefficient R≈0.7, significant with p<0.01) indicating mainly dynamically driven evaporation. The particular role of the Mediterranean Sea hints towards possible importance of Mediterranean moisture for the early-stage intensification of Vb-cyclones and the pre-moistening of the continental uptake regions upstream of the target catchments.
The Yacoraite Formation (Salta rift, Argentina) consists of Maastrichtian–Danian lacustrine carbonate and siliciclastic deposits with interbedded volcanic ash layers, organized in four third-order stratigraphic sequences. It offers the exceptional opportunity to jointly apply in situ zircon and carbonate U-Pb geochronology that resulted in two distinct depositional age depth models. Ages of the youngest zircon population from ash layers were linearly interpolated to derive a zircon depositional age depth model. A carbonate depositional age depth model was instead obtained from dated carbonate phases including microbialites, ooids, oncoids of calcitic and dolomitic mineralogy as well as early lacustrine calcite cements. Mean ages were defined from different carbonate phases belonging to the same layer and then linearly interpolated. Sedimentation rates were calculated from both depth models between pairs of dated samples and used to estimate the age of sequence boundaries, as well as the duration of the four stratigraphic sequences. The zircon and carbonate depositional age depth models agree with biostratigraphic constraints and exhibit excellent consistency. The onset and end of sedimentation were estimated at 68.2 ± 0.9 Ma and 62.3 ± 0.6 Ma (duration ca 5.7 Ma) via zircon geochronology and at 67.9 ± 1.7 Ma and 61.9 ± 1.3 Ma (duration ca 6.0 Ma) via carbonate geochronology. Results from this study show that with suitable samples and a newly implemented working strategy, in situ U-Pb dating of depositional and early diagenetic carbonates represent a valuable chronostratigraphic tool for estimating sedimentation rate and duration in poorly time-framed depositional systems.
Atmospheric particles play an important role in the radiative balance of the Earth, as well as they affect human health and air quality. Hence, the chemical characterization constitutes a crucial task to determinate their properties, sources and fate. Particularly, the analysis of nanoparticles (d<100 nm) represents an analytical challenge, since these particles are abundant in number but have very little mass.
This accumulative thesis focuses on the chemical characterization of nanoparticles, performed in both laboratory and field studies. Here, I present four manuscripts, two of which are my main project as a lead author.
The first manuscript (Caudillo et al., 2021) focuses on the gas and the particle phase originated from biogenic precursor gases (α-pinene and isoprene). The experiments were performed in the CLOUD chamber at CERN to simulate pure biogenic new particle formation. Both gas and particle phases are measured with a nitrate CI-APi-TOF mass spectrometer, while the TD-DMA is coupled to it for particle-phase measurements, this setup allows a direct comparison as both measurements use the identical chemical ionization and detector. This study demonstrates the suitability of the TD-DMA for measuring newly formed nanoparticles and it confirms that isoprene suppresses new particle formation but contributes to the growth of newly formed particles.
The second manuscript (Caudillo et al., 2022) presents an intercomparison of four different techniques (including the TD-DMA) for measuring the chemical composition of SOA nanoparticles. The measurements were conducted in the CLOUD chamber. The intercomparison was done by contrasting the observed chemical composition, the calculated volatility, and the thermal desorption behavior (for the thermal desorption techniques). The methods generally agreed on the most important compounds that are found in the nanoparticles. However, they did see different parts of the organic spectrum. Potential explanations for these differences are suggested.
The third manuscript (Ungeheuer al., 2022) presents both laboratory and ambient measurements to investigate the ability of lubricant oil to form new particles. These new particles are an important source of ultrafine particles in the areas nearby large airports. The ambient measurements were performed downwind of Frankfurt International Airport, and it was found that the fraction of lubricant oil is largest in the smallest particles. In the laboratory, the main finding was that evaporated lubricant oil nucleates and forms new particles rapidly. The results suggest that nucleation of lubricant oil and subsequent particle growth can occur in the cooling exhaust plumes of aircraft-turbofans.
The fourth manuscript (Wang et al., 2022) is a new particle formation study in the CLOUD chamber at CERN. This study shows that nitric acid, sulfuric acid, and ammonia interact synergistically and rapidly form particles under upper free tropospheric conditions. These particles can grow by condensation (driven by the availability of ammonia) up to CCN sizes and INP particles. The ability of these particles to act as a CCN and INP was also investigated and it was found to be as efficient as for desert dust. This mechanism constitutes an important finding and it can account for previous observations of high concentrations of ammonia and ammonium nitrate over the Asia monsoon region.
Diamonds growing in the Earth’s mantle often trap inclusions of fluids that are highly saline in composition. These fluids are thought to emerge from deep in subduction zones and may also be involved in the generation of some of the kimberlite magmas. However, the source of these fluids and the mechanism of their transport into the mantle lithosphere are unresolved. Here, we present experimental results showing that alkali chlorides are stable solid phases in the mantle lithosphere below 110 km. These alkali chlorides are formed by the reaction of subducted marine sediments with peridotite and show identical K/Na ratios to fluid inclusions in diamond. At temperatures >1100°C and low pressures, the chlorides are unstable; here, potassium is accommodated in mica and melt. The reaction of subducted sediments with peridotite explains the occurrence of Mg carbonates and the highly saline fluids found in diamonds and in chlorine-enriched kimberlite magmas.
Metasomatic reaction zones between mafic and ultramafic rocks exhumed from subduction zones provide a window into mass-transfer processes at high pressure. However, accurate interpretation of the rock record requires distinguishing high-pressure metasomatic processes from inherited oceanic signatures prior to subduction. We integrated constraints from bulk-rock geochemical compositions and petrophysical properties, mineral chemistry, and thermodynamic modeling to understand the formation of reaction zones between juxtaposed metagabbro and serpentinite as exemplified by the Voltri Massif (Ligurian Alps, Italy). Distinct zones of variably metasomatized metagabbro are dominated by chlorite, amphibole, clinopyroxene, epidote, rutile, ilmenite, and titanite between serpentinite and eclogitic metagabbro. Whereas the precursor serpentinite and oxide gabbro formed and were likely already in contact in an oceanic setting, the reaction zones formed by diffusional Mg-metasomatism between the two rocks from prograde to peak, to retrograde conditions in a subduction zone. Metasomatism of mafic rocks by Mg-rich fluids that previously equilibrated with serpentinite could be widespread along the subduction interface, within the subducted slab, and the mantle wedge. Furthermore, the models predict that talc formation by Si-metasomatism of serpentinite in subduction zones is limited by pressure-dependent increase in the silica activity buffered by the serpentine-talc equilibrium. Elevated activities of aqueous Ca and Al species would also favor the formation of chlorite and garnet. Accordingly, unusual conditions or processes would be required to stabilize abundant talc at high P-T conditions. Alternatively, a different set of mineral assemblages, such as serpentine- or chlorite-rich rocks, may be controlling the coupling-decoupling transition of the plate interface.
Talc formation via silica-metasomatism of ultramafic rocks is believed to play key roles in subduction zone processes. Yet, the conditions of talc formation remain poorly constrained. We used thermodynamic reaction-path models to assess the formation of talc at the slab-mantle interface and show that it is restricted to a limited set of pressure–temperature conditions, protolith, and fluid compositions. In contrast, our models predict that chlorite formation is ubiquitous at conditions relevant to the slab-mantle interface of subduction zones. The scarcity of talc and abundance of chlorite is evident in the rock record of exhumed subduction zone terranes. Talc formation during Si-metasomatism may thus play a more limited role in volatile cycling, strain localization, and in controlling the decoupling-coupling transition of the plate interface. Conversely, the observed and predicted ubiquity of chlorite corroborates its prominent role in slab-mantle interface processes that previous studies attributed to talc.
Key Points:
Limited talc formation by Si-metasomatism of ultramafic rocks in subduction zones
Chlorite formation is likely pervasive at the slab-mantle interface
Preferential formation of chlorite has wide-ranging chemical and physical implications for subduction zone processes
Plain Language Summary: In subduction zones, talc can form during chemical reactions of mantle rocks with silica-enriched fluids at the interface between descending oceanic plates and the overriding mantle. Its formation and distribution in subduction zones are believed to affect the volatile budget, rheological properties, and the down-dip limit of the decoupling of the slab-mantle interface. Therefore, illuminating the conditions that facilitate talc formation at high pressure-temperature conditions is key in assessing its roles in fundamental subduction zone processes. Using thermodynamic reaction-path models, we show that the formation of talc at the slab-mantle interface is restricted to a limited set of environmental conditions, because its formation is highly sensitive to the compositions of the mantle rocks and reactant fluids. Contrary to common belief, talc is unlikely to form in high abundance in ultramafic rocks metasomatized by Si-rich slab-derived fluids. Rather, our models predict the ubiquitous formation of chlorite along with other silicate minerals during Si-metasomatism due to the competing effects from other dissolved components that favor their formation over talc. This study calls into question the importance of talc during Si-metasomatism in subduction zones but highlights the more predominant role of chlorite.
Garnet xenocrysts from kimberlites provide unique insights into the composition, structure and evolution of the subcontinental lithospheric mantle (SCLM). For example, different metasomatic events in the SCLM are reflected in compositional differences between garnet xenocrysts. As mantle metasomatism largely controls the physical and chemical properties of the SCLM, it exerts first order control over the genesis of kimberlitic magmas and diamond formation. However, dating mantle lithologies and processes is complicated by high ambient temperatures that allow the equilibration of most isotopic systems up to the time of kimberlite eruption. As a consequence, the temporal connection between metasomatic events in the mantle and kimberlite genesis is commonly ambiguous.
In this study, we applied LA-ICPMS U-Pb dating to 43 harzburgitic, lherzolithic and megacrystic garnet xenocrysts from the ~376 Ma diamondiferous V. Grib kimberlite, Russia, in order to investigate the link between different types of mantle metasomatism and kimberlite genesis.
Our results indicate that, with two possible exceptions, only harzburgitic garnet overlaps in age with the kimberlite eruption, whereas lherzolitic and megacrystic garnet crystals are ~20 to 130 million years older. Furthermore, garnet U-Pb ages and Ni-in-garnet temperatures of ~820 to 1200 °C do not correlate. This, and the high closure temperature of U-Pb in garnet (≥900 °C) suggests that the garnet U-Pb ages indeed reflect metasomatic events in the SCLM. However, the U-Pb ages could also reflect cooling ages. In this case, the metasomatic events recorded in the garnet crystals must still have occurred up to ~130 million years prior to the eruption of the V. Grib kimberlite.
These findings have far-reaching implications for the genesis of (diamondiferous) kimberlites, as they clearly show that the time lag between metasomatic events in the SCLM, as recorded in kimberlitic garnet xenocrysts, and kimberlite eruption may extend to tens of millions of years.
Fossil records of early solar irradiation and cosmolocation of the CAI factory: a reappraisal
(2021)
Calcium-aluminum–rich inclusions (CAIs) in meteorites carry crucial information about the environmental conditions of the nascent Solar System prior to planet formation. Based on models of 50V–10Be co-production by in-situ irradiation, CAIs are considered to have formed within ~0.1 AU from the proto-Sun. Here, we present vanadium (V) and strontium (Sr) isotopic co-variations in fine- and coarse-grained CAIs and demonstrate that kinetic isotope effects during partial condensation and evaporation best explain V isotope anomalies previously attributed to solar particle irradiation. We also report initial excesses of 10Be and argue that CV CAIs possess essentially a homogeneous level of 10Be, inherited during their formation. Based on numerical modeling of 50V–10Be co-production by irradiation, we show that CAI formation during protoplanetary disk build-up likely occurred at greater heliocentric distances than previously considered, up to planet-forming regions (~1AU), where solar particle fluxes were sufficiently low to avoid substantial in-situ irradiation of CAIs.
Chloritoid and kyanite coexist in metapelites from the high-pressure/low-temperature Massa Unit in the Alpi Apuane metamorphic complex (Northern Apennines, Italy). The composition of chloritoid is extremely variable throughout the Massa Unit. Fe-chloritoid occurs in association with hematite-free, graphite-bearing schists, whereas strongly zoned Fe-Mg chloritoid is found with hematite and kyanite. We investigated the effect of different bulk Fe2O3 contents in controlling chloritoid composition through phase equilibria modelling of four selected samples, representative of the different chloritoid-bearing parageneses found in the Massa Unit. The ferric iron content, measured through wet chemical titration, ranges from 0 (graphite-chloritoid schist) to 73% of the total iron (hematite-chloritoid schist). We show that Mg-rich chloritoid compositions and stability of kyanite at greenschist to blueschist facies conditions can be reproduced in the MnO–Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O (MnNKFMASHTO) chemical system only considering the presence of significant amounts of ferric iron as part of the bulk composition. The stabilization of kyanite at lower grade is directly linked to the presence of Fe2O3, which renders the reactive bulk rock composition effectively enriched in Al2O3 with respect to Fe and Mg. We also document that high Fe2O3 contents exacerbate the effect of chloritoid fractionation, producing strongly zoned Fe-Mg-chloritoid grains. Finally, the P–T modelling of the Massa Units performed in this study allows, for the first time, the recognition of a two-stage evolution at peak conditions, with an earlier pressure peak (1.2–1.3 GPa at 350–400°C), and a later thermal peak (0.7–1.1 GPa at 440–480°C), compatible with subduction, underthrusting and exhumation of the Adria continental margin during growth of the Northern Apennine orogenic wedge.
The oxidation state of sulfur in slab fluids is controversial, with both dominantly oxidized and reduced species proposed. Here we use in situ X-ray absorption spectroscopy analysis of sulfur-in-apatite to monitor changes in the oxidation state of sulfur during high-P metasomatism by slab fluids in the subduction channel. Our samples include a 73 cm continuous transect of reaction zones between a metagabbroic eclogite block and serpentinite matrix from a mélange zone on the island of Syros, Greece. The block core consists of garnet, omphacite, phengite, paragonite, epidote-clinozoisite, and rutile. In this region, apatite is only observed as elongate inclusions in omphacite cores. From the core outwards micas are increasingly replaced by epidote-clinozoisite, garnets are smaller and more frequent, pyrite + bornite is observed as inclusions in recrystallized omphacite, and apatite is increasingly abundant in the matrix and inclusions in garnet. A major transition at 48 cm separates an assemblage of Ca-Na amphibole, omphacite, chlorite, pyrite, and apatite from the inner garnet-bearing eclogite assemblages. Omphacite disappears from the assemblage at ~56 cm and amphibole compositions sharply transition to tremolite at 59 cm. Finally, the assemblage tremolite + talc + pyrite is observed after ~70 cm.Apatites in the eclogite assemblages exclusively display S6+ peaks in their absorption spectra. This includes apatite inclusions in omphacite in the least altered lithology, as well as matrix apatite and isolated apatite inclusions in garnet in the outermost metasomatized eclogite zone. In the intermediate pyrite-rich (~1-5 vol %) amphibole + omphacite + chlorite zone, apatite displays a strong S1- absorption peak in most grains, with rare analyses showing mixed S1- and S6+. Finally, apatite in the outermost tremolite-bearing assemblages only displays a S6+ peak. The pyrite-rich zone at 48 cm occurs at the initial interface between the serpentinite matrix and eclogite block, characterized by a dramatic decrease in Na content and Mg#. Our data suggest that reduction of S6+ in infiltrating fluids to S1- in pyrite became focused as Fe diffused across the steep Mg# gradient, resulting in pyrite precipitation. In contrast, S reduction in the Mg-rich tremolite-dominant portions of the transect was limited by a lack of Fe, resulting in low modes of pyrite and fluid buffered S6+ in apatite. Finally, S6+-bearing apatite is also observed in reaction zone lithologies from elsewhere on Syros, suggesting our observations are not isolated.Two important conclusions are drawn from these data and observations: (1) In the case of Syros, slab fluids at eclogite-facies conditions carried oxidized S6+, and (2) The interaction of these fluids with eclogites composed of ferrous-Fe silicates resulted in extensive sulfide precipitation.
In subduction zones, sediments and hydrothermally altered oceanic crust, which together form part of the subducting slab, contribute to the chemical composition of lavas erupted at the surface to form volcanic arcs. Transport of this material from the slab to the overlying mantle wedge is thought to involve discreet melts and fluids that are released from various portions of the slab. We use a meta-analysis of geochemical data from eight globally representative arcs to show that melts and fluids from individual slab components cannot be responsible for the formation of arc lavas. Instead, the data are compatible with models that first invoke physical mixing of slab components and the mantle wedge, widely referred to as high-pressure mélange, before arc magmas are generated.
Sulfur in the slab: a sulfur-isotopes and thermodynamic-modeling perspective from exhumed terranes
(2022)
Sulfur is a key element in the subduction zone-volcanic arc system; however, the mechanism(s) that recycle sulfur from the slab into the overlying volcanic arc are debated. Here we summarize recent advances in quantifying this component of the deep sulfur cycle. First, primary metamorphic or inherited sulfides in oceanic-type eclogites are only rarely observed as inclusions and are typically absent from the rock matrix. Additionally, sulfides are relatively common in rocks metasomatized at the slab-mantle interface by slab-derived fluids during exhumation. Combined, these two observations suggest that sulfur loss from subducted mafic crust is relatively efficient. Thermodynamic modeling in Perple_X using the Holland and Powell (2011) database combined with the Deep Earth Water model suggests that the efficiency and speciation of sulfur loss varies depending on the degree of seafloor alteration prior to subduction and the geothermal gradient of the slab. In relatively cold subduction zones, such as Honshu, slab-fluids derived from subducted mafic crust are predicted to exhibit elevated concentrations of HSO4-, SO42-, HSO3-, and CaSO4(aq), whereas hot subduction zones, such as Cascadia, are predicted to produce slab fluids enriched in HS- and H2S at lower pressures. The oxidation of sulfur expelled from subducted pyrite is balanced by the reduction of Fe3+ to Fe2+, consistent with the low Fe3+/SFe of exhumed eclogites relative to blueschists and altered oceanic crust. Where oxidized S-bearing fluids are produced, they are anticipated to interact with more reduced rocks at the slab-mantle interface and within the mantle wedge, resulting in sulfide precipitation and significant isotopic fractionation. The δ34S values of slab fluids are estimated to fall between -11 and +8 ‰. Rayleigh fractionation during progressive fluid-rock interaction results in fractionations of tens of per mil as oxidized species are depleted and sulfides are precipitated, resulting in δ34S values of sulfides that easily span the -21.7 to +13.9 ‰ range observed in metasomatic sulfides in exhumed high-pressure rocks. However, in subduction zones where reduced species prevail, the S isotopic signature of slab fluids is expected to reflect their source and will exhibit a narrower range in δ34S values. As a result, the δ34S values measured in arc magmas may not always be a reliable indicator of the contribution of different components of the slab, such as sediments vs. AOC. Additionally, the impact of S recycling on the oxygen fugacity of arc magmas is expected to vary both spatially and temporally throughout Earth history.
This chapter reviews the boron isotopic composition of the ocean floor, including pristine igneous oceanic crust such as mid-ocean ridge basalts and ocean island basalts and their implications for the B isotopic composition of the mantle. The chapter further discusses the B isotopic effects of assimilation of altered crustal materials in mantle-derived magmas. The systematics of seawater alteration on oceanic rocks are discussed, including sediments, igneous crust and serpentinization of ultramafic rocks and the respective marine hydrothermal vent fluids. The chapter concludes with a discussion of the secular evolution of the B isotopic composition of seawater.
Titanite is a potentially powerful U–Pb petrochronometer that may record metamorphism, metasomatism, and deformation. Titanite may also incorporate significant inherited Pb, which may lead to inaccurate and geologically ambiguous U–Pb dates if a proper correction is not or cannot be applied. Here, we present laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)-derived titanite U–Pb dates and trace element concentrations for two banded calcsilicate gneisses from south-central Maine, USA (SSP18-1A and SSP18-1B). Single spot common Pb-corrected dates range from 400 to 280 Ma with ±12–20 Ma propagated 2SE. Titanite grains in sample SSP18-1B exhibit regular core-to-rim variations in texture, composition, and date. We identify four titanite populations: (1) 397 ± 5 Ma (95% CL) low Y + HREE cores and mottled grains, (2) 370 ± 7 Ma high Y + REE mantles and cores, (3) 342 ± 6 Ma cores with high Y + REE and no Eu anomaly, and (4) 295 ± 6 Ma LREE-depleted rims. We interpret the increase in titanite Y + HREE between ca. 397 and ca. 370 Ma to constrain the timing of diopside fracturing and recrystallization and amphibole breakdown. Apparent Zr-in-titanite temperatures (803 ± 36°C at 0.5 ± 0.2 GPa) and increased XDi suggest a thermal maximum at ca. 370 Ma. Population 3 domains dated to ca. 342 Ma exhibit no Eu anomaly and are observed only in compositional bands dominated by diopside (>80 vol%), suggesting limited equilibrium between titanite and plagioclase. Finally, low LREE and high U/Th in Population 4 titanite dates the formation of hydrous phases, such as allanite, during high XH2O fluid infiltration at ca. 295 Ma. In contrast to the well-defined date–composition–texture relationships observed for titanite from SSP18-1B, titanite grains from sample SSP18-1A exhibit complex zoning patterns and little correlation between texture, composition, and date. We hypothesize that the incorporation of variable amounts of radiogenic Pb from dissolved titanite into recrystallized domains resulted in mixed dates spanning 380–330 Ma. Although titanite may reliably record multiple phases of metamorphism, these data highlight the importance of considering U–Pb data along with chemical and textural data to screen for inherited radiogenic Pb.
Reliable identification of chondrules, calcium-aluminum-rich inclusions (CAIs), carbonate grains, and Ca-phosphate grains at depth within untouched, unprepared chondritic samples by a nondestructive analytical method, such as synchrotron X-ray fluorescence (SXRF) computed tomography (CT), is an essential first step before intrusive analytical and sample preparation methods are performed. The detection of a local Ca-enrichment could indicate the presence of such a component, all of which contain Ca as major element and/or Ca-bearing minerals, allowing it to be precisely located at depth within a sample. However, the depth limitation from which Ca-K fluorescence can travel through a chondrite sample (e.g., ∼115 µm through material of 1.5 g cm−3) to XRF detectors leaves many Ca-bearing components undetected at deeper depths. In comparison, Sr-K lines travel much greater distances (∼1700 µm) through the same sample density and are, thus, detected from much greater depths. Here, we demonstrate a clear, positive, and preferential correlation between Ca and Sr and conclude that Sr-detection can be used as proxy for the presence of Ca (and, thus, Ca-bearing components) throughout mm-sized samples of carbonaceous chondritic material. This has valuable implications, especially for sample return missions from carbonaceous C-type asteroids, such as Ryugu or Bennu. Reliable localization, identification, and targeted analysis by SXRF of Ca-bearing chondrules, CAIs, and carbonates at depth within untouched, unprepared samples in the initial stages of a multianalysis investigation insures the valuable information they hold of pre- and post-accretion processes in the early solar system is neither corrupted nor destroyed in subsequent processing and analyses.
Questions: Both species turnover and intraspecific trait variation can affect plant assemblage dynamics along environmental gradients. Here, we asked how community assemblage patterns in relation to species turnover and intraspecific variation differ between endemic and non-endemic species. We hypothesized that endemic species show lower intraspecific variation than non-endemic species because they tend to have high rates of in situ speciation, whereas non-endemic species are expected to have a larger gene pool and higher phenotypic plasticity.
Location: La Palma, Canary Islands.
Methods: We established 44 sampling sites along a directional gradient of precipitation, heat load, soil nitrogen, phosphorus and pH. Along this gradient, we estimated species abundances and measured three traits (plant height, leaf area and leaf thickness) on perennial endemic and non-endemic plant species. In total, we recorded traits for 1,223 plant individuals of 43 species. Subsequently, we calculated community-weighted mean traits to measure the relative contribution of species turnover, intraspecific variation and their covariation along the analysed gradient.
Results: The contribution of intraspecific variation to total variation was similar in endemic and non-endemic assemblages. For plant height, intraspecific variation explained roughly as much variation as species turnover. For leaf area and leaf thickness, intraspecific variation explained almost no variation. Species turnover effects mainly drove trait responses along the environmental gradient, but intraspecific variation was important for responses in leaf area to precipitation.
Conclusions: Despite their distinct evolutionary history, endemic and non-endemic plant assemblages show similar patterns in species turnover and intraspecific variation. Our results indicate that species turnover is the main component of trait variation in the underlying study system. However, intraspecific variation can increase individual species’ fitness in response to precipitation. Overall, our study challenges the theory that intraspecific trait variation is more important for the establishment of non-endemic species compared with endemic species.
Positive plant–plant interactions are thought to drive vegetation patterns in harsh environments, such as semi-arid areas. According to the stress-gradient hypothesis (SGH), the role of positive interactions between species (facilitation) is expected to increase with harshness, predicting associated variation in species composition along environmental gradients. However, the relation between stress and facilitation along environmental gradients is debated. Furthermore, differentiating facilitative interactions from other underlying mechanisms, such as microtopographic heterogeneity, is not trivial. We analysed the spatial co-occurrence relationships of vascular plant species that form patchy vegetation in arid lapilli fields (tephra) from recent volcanic eruptions on La Palma, Canary Islands. Assuming a harshness gradient negatively correlated with elevation because the lower elevations are more arid and water availability is considered the most limiting resource, and that an outcome of facilitation is plants co-occurring in the same patch, from the SGH we expected a greater degree of co-occurrence at lower elevation. We tested this at both the species and the individual plant level. We analysed the species composition of 1277 shrubby vegetation patches at 64 different sampling points, ranging from the coast to around 700 m a.s.l. Patch morphology and microtopographic heterogeneity variables were also measured, to account for their potential effects on the species composition of patches. We used generalized linear models and generalized mixed-effects models to analyse species richness, number of individuals in patches and percentage of patches with positive co-occurrences, and a pairwise co-occurrence analysis combined with a graphical network analysis to reveal positive links between 13 of the species. We found that the percentage of patches with positive co-occurrences increased at higher elevations, in contrast to the predictions of the SGH, but in accordance with a refined stress-gradient hypothesis for arid sites, in which characteristics of the interacting species are incorporated.
This thesis presents the experimental and numerical analysis of seismic waves that are produced by wind farms. With the aim to develop renewable energies rapidly, the number of wind turbines has been increased in recent years. Ground motions induced by their operation can be observed by seismometers several kilometers away. Hence, the seismic noise level can be significantly increased at the seismic station. Therefore, this study combines long-term experiments and numerical simulations to improve the understanding of the seismic wavefields emitted by complete wind farms and to advance the prediction of signal amplitudes.
Firstly, wind-turbine induced signals that are measured at a small wind farm close to Würzburg (Germany) are correlated with the operational data of the turbines. The frequency-dependent decay of signal amplitudes with distance from the wind farm is modeled using an analytical method including the complex effects of interferences of the wavefields produced by the multiple wind turbines. Specific interference patterns significantly affect the wave propagation and therefore the signal amplitude in the far field of a wind farm. Since measurements inside the wind turbines show that the assumption of in-phase vibrating wind turbines is inappropriate, an approach to calculate representative seismic radiation patterns from multiple wind turbines, which allows the prediction of amplitudes in the far field of a complete wind farm, is proposed.
In a second study, signals with a frequency of 1.15 Hz, produced by the Weilrod wind farm (north of Frankfurt, Germany) are observed at the seismological observatory TNS (Taunus), which is located at a distance of 11 km from the wind farm. The propagation of the wavefield emitted by the wind farm is numerically modeled in 3D, using the spectral element method. It is shown that topographic effects can cause local signal amplitude reductions, but also signal amplification along the travel path of the seismic wave. The comparison of simulations with and without topography reveals that the reduction and amplification are spatially linked to the shape of the topography, which could be an explanation for the relatively high signal amplitude observed at TNS.
Finally, the reduction of the impact of wind turbines on seismic measurements using borehole installations is studied using 2D numerical models. Possible effects of the seismic velocity, attenuation, and layering of the subsurface are demonstrated. Results show that a borehole can be very effective in reducing the observed high-frequency signals emitted by wind turbines. However, a borehole might not be beneficial if signals with frequencies of about 1 Hz (or lower) are of interest, due significant wavelength-dependent effects. The estimations of depth-dependent amplitudes with a layered subsurface are validated with existing data from wind-turbine-induced signals measured at the top and bottom of two boreholes.
The experimental analysis of measurements conducted at wind farms and the advances of modeling such signals improve the understanding of the propagation of wind-farm induced seismic wave fields. Furthermore, the methods developed in this work have a high potential of universal application to the prediction of signal amplitudes at seismometers close to wind farms with arbitrary layout and geographic location.
Nontarget screening exhibits a seasonal cycle of PM2.5 organic aerosol composition in Beijing
(2022)
The molecular composition of atmospheric particulate matter (PM) in the urban environment is complex, and it remains a challenge to identify its sources and formation pathways. Here, we report the seasonal variation of the molecular composition of organic aerosols (OA), based on 172 PM2.5 filter samples collected in Beijing, China, from February 2018 to March 2019. We applied a hierarchical cluster analysis (HCA) on a large nontarget-screening data set and found a strong seasonal difference in the OA chemical composition. Molecular fingerprints of the major compound clusters exhibit a unique molecular pattern in the Van Krevelen-space. We found that summer OA in Beijing features a higher degree of oxidation and a higher proportion of organosulfates (OSs) in comparison to OA during wintertime, which exhibits a high contribution from (nitro-)aromatic compounds. OSs appeared with a high intensity in summer-haze conditions, indicating the importance of anthropogenic enhancement of secondary OA in summer Beijing. Furthermore, we quantified the contribution of the four main compound clusters to total OA using surrogate standards. With this approach, we are able to explain a small fraction of the OA (∼11–14%) monitored by the Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM). However, we observe a strong correlation between the sum of the quantified clusters and OA measured by the ToF-ACSM, indicating that the identified clusters represent the major variability of OA seasonal cycles. This study highlights the potential of using nontarget screening in combination with HCA for gaining a better understanding of the molecular composition and the origin of OA in the urban environment.
Vladimir Vernadsky's concept of living matter is central to his biogeochemistry, the science he founded. For several reasons, his original understanding of living matter is one of the most complex notions in the history of the life sciences. First, biogeochemistry is by definition an interdisciplinary enterprise that embraces biology, including evolutionary theory, geology, and chemistry, and combines them into a unique research program. Second, if understood in the original sense as used by Vernadsky, living matter is a concept built into idiosyncratic metaphysics constructed around the so-called principle of life's eternity. Third, the concept of living matter reflects the specificity of Vernadsky's sophisticated philosophy of science as he insisted that 'scientific thought' is a planetary phenomenon as well as a geological force. In our contribution, we will introduce Vernadsky's concept of living matter in its historical context. Accordingly, we will also give some chronology of Vernadsky's work related to the growth of his biosphere concept highlighting the 'Ukrainian' period as it is in this period that he intensively elaborated on the notion of living matter. This will be followed by his theory of living matter as it was formulated in his major works of the later period. We are going to locate the notion of living matter within Vernadsky's theoretical system and demonstrate that he regarded his theory of the living as an evolutionary theory complementary to that of Charles Darwin from the very beginning. Additionally, we will briefly present Vladimir Beklemishev's concept of 'geomerida' which he developed at approximately the same time as Vernadsky was elaborating on his 'living matter' to highlight the specificity of the latter's methodology.
This thesis is focusing on the impact of Paratethys and Mediterranean water bodies over the Eurasian climate and the interplay between climate, tectonics and biosphere during the late Miocene. This target was the interval between 12.7 and 7.65 Ma for Paratethys, following the Eastern Paratethys restriction and isolation, and 7.2−6.5 Ma (the early Messinian) in Mediterranean, zooming on the effects of gateway restrictions over the eastern Mediterranean and the new born Aegean domain. In both cases restriction is overlapping with large scale climatic changes and tectonic reconfiguration, leading a sort of symbiotic relationship.
Paratethys was a giant epicontinental sea that covered a large part of Eurasia since Paleogene. Due to the Eurasia-Afro-Arabia collision and formation of the Alpine-Himalayan belt (Rögl, 1999; Popov et al., 2006), the Paratethys was divided during the late Miocene in smaller basins that in time were isolated of each other. The protracted isolation and intense continentalisation of paratethyan realm led to changes in humidity distribution, basin connectivity, sediment sources and salinity. These changes had in turn major consequences over water circulation, water availability, vegetation cover and biota. These changes are more intense after 11.6 Ma, when the Eastern Paratethys lost any sustained marine connection, evolving into an enclosed system with endemic fauna (Harzhauser and Piller, 2007).
Mediterranean Sea is a Mezozoic oceanic relic squeezed between Africa, Europe, Anatolia and Arabia, as Africa continued to subduct beneath the European plate. As opposed to Paratethys, it maintained the open connection with the ocean until Messinian, when the two Atlantic gateways (Betic and Rifian corridors) closed for a short time, isolating the basin. The cut off resulted in a dramatic drop down and onset of evaporitic precipitation in marginal basins, the event receiving the name of Messinian Salinity Crisis (5.97−5.55). The restriction affected all marine ecosystems, due to changes in salinity and stratification of water column.
The main objectives of this thesis were:
(1) build valid paleo-temperatures records for both basins based on biomarkers;
(2) reconstruct the hydrology for the late Miocene time interval;
(3) identify vegetation composition and changes;
(4) identify paleo-fires in the late Miocene sediment records;
(5) identify the biotic response to the overall climate and tectonic changes.
All the above objectives were attained with results published in specific journals (Chapters 5−7).
Based on Panagia section (Taman Peninsula, Russia) the longest Paratethys temperature record was completed (~5 Myr), covering the interval between 12.7 and 7.65 Ma. A comprehensive SST and MAT records was obtained, as well as soil pH and carbon (δ13C) and hydrogen (δ2H) stable isotopic compositions on n-alkanes and alkenones. The main findings are concentrated around three prolonged periods with severe droughts affecting the late Miocene circum-Paratethys region peaking at 9.65, 9.4 and 7.9 Ma, associated with a transition towards open land vegetation, intensification of fire activity and enhanced evaporation and aridity.
The time intervals with dryer conditions recorded in Panagia coincide with periods of mammal turnover and dispersal in Eurasia indicating that major environmental changes occurred in the circum-Paratethys region and Paratethys fragmentation had a great impact on the terrestrial ecosystems, when periods of prolonged droughts generated biotic crises and animal displacements across the Eurasian continent. The δ13CC29n-alkane values and charcoal morphologies from Panagia indicate an increased contribution of C4 plants adapted to drier conditions at 9.66 Ma. Similarly high δ13CC29n-alkane values continue until 9.4 Ma, when in Western Europe increased seasonality accelerated the demise of the evergreen subtropical woodlands and expansion of grasslands from Anatolia and Middle East to Europe.
As a result of basin fragmentation and climatic stress, the Eastern Paratethys sub-basins progressively lost their marine properties and turned into brackish-fresh water bodies fed primarily by riverine input. The shallower areas became in time emerged, obstructing connections and isolating the biota, inducing rapid adjusting or extinctions. Thus, the Paratethys harbored a highly endemic fauna (Rögl, 1999), such as dwarf whales, dolphins, seals (among mammals), as well as fish and other taxa (mollusks, ostracods, diatoms, foraminifera, algae, etc.).
Collectively the data structured and analyzed in chapter five support a model in which the Eastern Paratethys evolved as a largely (en)closed system, registering paleoenvironmental signals that are governed by interbasinal connectivity (or lack of it) and regional climate changes in the basin catchment. Acting as an important source of humidity for Western and Central Asia, the size and areal extent of the Paratethys water body is likely to have had a major impact on hydroclimate patterns in the Eurasian interior, with the cumulative fluctuations in both hydrology and surface temperature enhancing the aridity and seasonality, with different partition of moisture over the year. Our combined data suggests a decoupling of Paratethys from the global system as isolation advanced, dominated by regional tectonics and ultimately the Paratethys volume and areal extent reduction.
WaterGAP (Water - Global Assessment and Prognosis) is a tool for modeling global water use and water availability. It participates among other models in the ISIMIP initiative (The Inter-Sectoral Impact Model Intercomparison Project). As part of this initiative, the water temperature should be calculated by participating hydrological models because it plays a vital role in many chemical, physical and biological processes. Therefore, the subject of this master thesis is to implement the physically based surface water temperature computation after VAN BEEK ET AL. (2012) and WANDERS ET AL. (2019) into WaterGAP and compare the results to the statistical regression approach by PUNZET ET AL. (2012). The computation is validated with observed water temperature data obtained from the GEMStat water quality database. The results are good for arctic and temperate latitudes. Surface water temperatures for tropical rivers are overestimated, most likely due to the overestimation of precipitation temperatures, incoming radiation and groundwater temperatures. The comparison with the regression model by PUNZET ET AL. (2012) shows matching results. The regression model even matches with WaterGAP results for most of the simulations of the future under climate change conditions, where the regression model should stop working due to changing environmental parameters. Several assumptions had to be made in order to implement the water temperature calculation in Water-GAP. These include, e.g., discharge temperatures for power plant cooling water, precipitation and surface runoff temperatures. For model improvements, perhaps three different values for the different regions of the world should be used to cool down the precipitation and surface runoff. The model could also be improved by refining the ice formation calculation, especially for the conditions when the ice melts, breaks up and is transported downstream. Furthermore, the feedback to the river channel roughness could be implemented if ice has formed. The WaterGAP model upgraded with the water temperature calculation will help the ISIMIP initiative in the future.
The reanalysis products and derived products, ERA5 (Copernicus Climate Change Service, 2018) and W5E5 (WATCH Forcing Data (WFD) methodology applied to ERA5) (LANGE ET AL., 2021) have been recently published initiating a new phase of scientific research utilizing these datasets. ERA5 and W5E5 offer the possibility to reduce insecurities in model results through their improved quality compared to previous climate reanalyses (CUCCHI ET AL., 2020). The suitability of either climate forcing as input for the hydrological model WaterGAP and the influence of the models specific calibration routine has been evaluated with four model experiments. The model was validated by analysing the models ability to produce reasonable values for global water balance components and to reproduce observed discharge in 1427 basins as well as total water storage anomalies in 143 basins using well established efficiency metrics. Bias correction of W5E5 was found to lead to more global realistic mean precipitation and consequently discharge and AET values. In an uncalibrated model setup ERA5 results in better performances across all efficiency metrics. Model results produced with W5E5 as climate input were strongly improved through calibration ultimately leading to the best performances out of all four model experiments. However, model performances considerably improved through calibration with both climate forcings hence calibration was found to have the strongest effect on model performance. Furthermore, spatial differences in performance of either forcing were identified. Snow-dominated regions show an overall better performance with ERA5, while wetter and warmer regions are better represented with W5E5. Finally, it can be concluded that W5E5 should be preferred as climate input for impact modelling; however, depending on the spatial scale and region ERA5 should at least be considered, in particular for snow-dominated regions.
The crystal structure of the high temperature phase of anilinium bromide, C6H5NH3⊕Br⊖ , was studied by X-ray and neutron diffraction at T = 343 K. The refinement supports disordered positions of the -NH3⊕ group. A split-atom model is proposed which includes disorder of the benzene ring. The thermal parameters, hydrogen bond distances, and other experimental data (NMR, NQR, inelastic neutron scattering) are in accordance with this model.
Ob Klimawandel oder Luftverschmutzung: Die chemischen und physikalischen Prozesse in der Atmosphäre haben wichtige Auswirkungen auf die menschliche Gesundheit und Ökosysteme. Dabei ist die Atmosphäre mehr als ein Gemisch aus Stickstoff, Sauerstoff, Wasserdampf, Helium und Kohlenstoffdioxid. Es gibt zahlreiche Spurengase, deren Gesamtanteil am Volumen weniger als 1 % ausmacht. In dieser Arbeit werden Stickstoffoxide, Schwefeldioxid, Kohlenstoffmonoxid und Schwefelsäure näher betrachtet, die im Rahmen der flugzeugbasierten Messkampagne Chemistry of the Atmosphere: field experiment in Europe (CAFE-EU)/BLUESKY gemessen wurden.
Die Stickstoffoxide NO und NO2, als NOx zusammengefasst, besitzen hauptsächlich anthropogene Quellen, allen voran fossile Verbrennung und industrielle Prozesse. Zwischen NO und NO2 besteht ein photochemisches Gleichgewicht, sodass in der Atmosphäre vor allem NO2 in relevanten Konzentrationen vorkommt; dies wirkt aufgrund der Bildung von Salpetersäure, HNO3, in wässriger Lösung beim Einatmen ätzend und ist entsprechend gesundheitsschädlich. Troposphärisches Ozon, O3, wesentlicher Bestandteil von Sommersmog, wird hauptsächlich durch die Reaktion von NO mit Peroxiden (HO2 und RO2) gebildet. In der Stratosphäre entstehen NOx hauptsächlich durch die Photodissoziation von Lachgas, N2O, das aufgrund seiner langen Lebenszeit von der Tropo- in die Stratosphäre transportiert werden kann und dort die wichtigste Stickstoffquelle darstellt. In der Stratosphäre tragen NOx zum katalytischen Abbaumechanismus des Ozons bei (Bliefert, 2002; Seinfeld and Pandis, 2016).
Schwefeldioxid, SO2, ist ein toxisches Gas, dessen atmosphärische Quellen hauptsächlich anthropogen sind, nämlich fossile Verbrennung und industrielle Prozesse; Senken sind trockene und feuchte Deposition, wobei letztere zu saurem Regen führen kann. Seit den 1980ern sinken die globalen SO2-Emissionen. SO2 kann in der Atmosphäre zu Sulfat und Schwefelsäure oxidiert werden, was Hauptbestandteil des Wintersmogs ist. Der wichtigste Mechanismus ist die Oxidation mit dem Hydroxylradikal, OH˙, unter Beteiligung von Wasserdampf. In der Stratosphäre ist Carbonylsulfid, OCS, die wichtigste Schwefelquelle, da es analog zum N2O dank seiner langen Lebenszeit von der Tropo- in die Stratosphäre transportiert werden kann (Bliefert, 2002; Seinfeld und Pandis, 2016). Typische Konzentrationen von Schwefelsäure sind 105 cm–3 nachts und 107 cm–3 tagsüber in der Troposphäre sowie 105 cm–3 tagsüber in der Stratosphäre (Clarke et al., 1999; Weber et al., 1999; Fiedler et al., 2005; Arnold, 2008; Kürten et al., 2016; Berresheim et al., 2000).
Kohlenstoffmonoxid, CO, ist ein toxisches Gas, das zu gleichen Teilen durch direkte Emissionen (v.a. Biomasseverbrennung und fossile Verbrennung) und In-situ-Oxidation (v.a. von Methan, Isopren und industriellen Kohlenwasserstoffen) in die Atmosphäre gelangt. Die Hauptsenke ist die Reaktion mit OH˙ in der Troposphäre. Seit 2000 sinkt die globale CO-Konzentration (Bliefert, 2002).
Doch neben Gasen sind auch Aerosolpartikel fester Bestandteil des Gemisches Luft, welche luftgetragene feste oder flüssige Teilchen sind. Primäre Aerosolpartikel werden direkt als solche in die Atmosphäre emittiert, während sekundäre Aerosolpartikel in der Atmosphäre gebildet werden, indem gasförmige Vorläufersubstanzen mit geringer Flüchtigkeit auf primären Partikeln kondensieren oder durch Zusammenclustern und Anwachsen komplett neue Partikel bilden. Aerosolpartikel ermöglichen als Wolkenkondensationskeime erst die Bildung von Wolken und wirken somit – neben ihrem direkten reflektierenden Effekt – durch Änderung der Wolkenbedeckung und -eigenschaften insgesamt kühlend aufs Klima und beeinflussen die lokalen und globalen Wasserkreisläufe. Doch sie haben auch negative Auswirkungen auf die menschliche Gesundheit und sind für eine Verkürzung der durchschnittlichen Lebensdauer in Regionen mit hohen Feinstaubbelastungen verantwortlich (Seinfeld und Pandis, 2016; Bellouin et al., 2020; World Health Organization, 2016).
Neben den bisher betrachteten neutralen, also ungeladenen Gasen und Partikeln sind Ionen in der Gasphase sowie geladene Partikel ebenfalls Bestandteil der Atmosphäre. Sie spielen bei vielen atmosphärischen Prozessen eine wichtige Rolle, wie etwa bei Gewittern, Radiowellenübertragung und ionen-induzierter Nukleation von Aerosolpartikeln. Die Hauptquellen für Ionisation in der Tropo- und Stratosphäre ist die galaktische kosmische Strahlung, die entgegen ihrem Namen hauptsächlich aus Protonen und α-Partikeln (primäre Partikel genannt) besteht und in der Erdatmosphäre durch Kollision mit Luftmolekülen Teilchenschauer von sekundären Partikeln (u.a. Myonen, Pionen und Neutrinos) hervorruft. Die primären und sekundären Partikel können die Luftmoleküle ionisieren unter Entstehung von N+, N2+, O+, O2+ und Elektronen. Sauerstoff reagiert rasch mit letzteren zu O– und O2–. Diese Kationen und Anionen reagieren weiter, bis Ionenclustern der Summenformeln (HNO3)n(H2O)mNO3– und H+(H2O)n(B)m gebildet werden, wobei B Basen wie Methanol, Aceton, Ammoniak oder Pyridin sind. Weitere Ionisationsquellen sind der Zerfall des Radioisotops 222Rn in Bodennähe und ionisierende Solarstrahlung oberhalb der Stratosphäre. Atmosphärische Ionen haben zwei wichtige Senken: die Wiedervereinigung, auch Rekombination genannt, bei der sich ein Kation und ein Anion gegenseitig neutralisieren sowie das Anhaften an Aerosolpartikeln. Letztere Senke ist vor allem in der Troposphäre aufgrund der relativ hohen Konzentration an Aerosolpartikeln relevant (Arnold, 2008; Viggiano und Arnold, 1995; Bazilevskaya et al., 2008; Hirsikko et al., 2011).
Melting inside earth is a common phenomenon and can be observed in many different regions where melt travels through the mantle and crust to eventually reach the surface where it crystallizes to build large volcanic provinces, whole stratigraphic layers of flood basalts, or even the oceanic crust. Often, melt reaching the surface is a good source of information. It can be used to achieve a better understanding about processes taking place in deeper regions inside the mantle and it is therefore essential to fundamentally understand melting and melt percolation processes. In order to achieve a deeper understanding, the aim of this thesis is to investigate processes that are connected to melting by using numerical models.
The physical model used is a so called two-phase flow model which describes the ability of melt to percolate through a viscously deforming, partially molten matrix. A famous feature of two-phase flow are solitary porosity waves, which are waves of locally higher porosity ascending through a partially molten background, keeping its shape constant, driven by decompaction and compaction of the solid matrix in front and behind the wave.
The viscosity law for shear- and volume viscosity was strongly simplified in most previous studies that modeled solitary waves. Often the porosity dependency is underestimated or its influence on the volume viscosity is even neglected, leading to too high viscosities. In this work more realistic laws are used that strongly decrease for small melt fractions. Those laws are incorporated into a 2D Finite Difference mantle convection code with two-phase flow to study the ascent of solitary porosity waves.
The model results show that an initial Gaussian-shaped wave rapidly evolves into a solitary wave with a certain amplitude, traveling upwards with constant velocity. Even though strongly weaker viscosities are used, the effect on dispersion curves and wave shape are only minor as long as the background porosity is rather small. The results are still in agreement to semi-analytical solutions which neglect shear stresses in the melt segregation equation. Higher background porosities and wave amplitudes lead to significant decrease in phase velocity and wave width, as the viscosity is strongly effected. However, the models show that solitary waves are still a possible mechanism for more realistic matrix viscosities.
While the ascending of porosity waves are mostly described by the movement of fluid melt, partially molten regions inside Earth trigger upwelling of both, solid and fluid phases, which can be called diapirism. While diapirs can have a wide variety of wavelengths, porosity waves are restricted to a few times the compaction length. The size of a melt perturbation in terms of compaction length therefore describes whether material is transported by diapirism or porosity waves. In this thesis we study the transition from diapiric rise to solitary porosity waves by systematically changing the size of a porosity perturbation from 1.8 to 120 times the compaction length. In case of a perturbation of the size of a few times the compaction length a single porosity wave will emerge, either with a positive or negative vertical matrix flux and if melt is not allowed to move relative to the matrix a diapir will emerge. In between these physical end members a regime can be observed where the partially molten perturbation will split up into numerous solitary waves, whose phase velocity is low compared to the Stokes velocity and the swarm of solitary waves will ascend jointly as a diapir, slowly elongating due to a higher amplitude main solitary wave.
Solitary waves will always emerge from a melt perturbation as long as two-phase flow is enabled, but the time for a solitary wave to emerge increases non-linearly with the perturbation radius in terms of compaction length. In nature, in many cases this time might be too long for solitary waves to emerge.
Another important feature when it comes to two-phase flow is the transport of trace elements in melt. Incompatible elements prefer to go into the melt, which eventually enriches the area where it crystallizes again. In order to model this redistribution, the code FDCON was extended to allow for fully consistent transport of elements in melt, including melting, freezing and re-equilibration with time. A 2D model, a simple representation of a volcanic back arc, is set up to investigate the behavior of trace elements. The influence of retention number and re-equilibration time is examined. Lava-lamp like convection can be observed in the lower part of the model, producing melt, that eventually leads to enrichment in trace elements in the upper high-viscous layer. The total enrichment in this layer approaches an asymptotic value and a 0D model is introduced to recreate this behavior.