550 Geowissenschaften
Refine
Year of publication
- 2021 (85) (remove)
Document Type
- Article (85) (remove)
Has Fulltext
- yes (85)
Is part of the Bibliography
- no (85)
Keywords
- Baltic age spectra (2)
- COSMO-CLM (2)
- Detrital zircons (2)
- Eocene (2)
- Holy Cross Mountains (2)
- Mid-German Crystalline Zone (2)
- Odenwald (2)
- U–Pb ages (2)
- Variscides (2)
- 18S rRNA gene (1)
Institute
We present the first oxidation state measurements for the subcontinental lithospheric mantle (SCLM) beneath the Rae craton, northern Canada, one of the largest components of the Canadian shield. In combination with major and trace element compositions for garnet and clinopyroxene, we assess the relationship between oxidation state and metasomatic overprinting. The sample suite comprises peridotite xenoliths from the central part (Pelly Bay) and the craton margin (Somerset Island) providing insights into lateral and vertical variations in lithospheric character. Our suite contains spinel, garnet-spinel and garnet peridotites, with most samples originating from 100 to 140 km depth. Within this narrow depth range we observe strong chemical gradients, including variations in oxygen fugacity (ƒO2) of over 4 log units. Both Pelly Bay and Somerset Island peridotites reveal a change in metasomatic type with depth. Observed geochemical systematics and textural evidence support the notion that Rae SCLM developed through amalgamation of different local domains, establishing chemical gradients from the start. These gradients were subsequently modified by migrating melts that drove further development of different types of metasomatic overprinting and variable oxidation at a range of length scales. This oxidation already apparent at ~ 100 km depth could have locally destabilised any pre-existing diamond or graphite.
Plant community biomass production is co-dependent on climatic and edaphic factors that are often covarying and non-independent. Disentangling how these factors act in isolation is challenging, especially along large climatic gradients that can mask soil effects. As anthropogenic pressure increasingly alters local climate and soil resource supply unevenly across landscapes, our ability to predict concurrent changes in plant community processes requires clearer understandings of independent and interactive effects of climate and soil. To address this, we developed a multispecies phytometer (i.e., standardized plant community) for separating key drivers underlying plant productivity across gradients. Phytometers were composed of three globally cosmopolitan herbaceous perennials, Dactylis glomerata, Plantago lanceolata, and Trifolium pratense. In 2017, we grew phytometer communities in 18 sites across a pan-European aridity gradient in local site soils and a standardized substrate and compared biomass production. Standard substrate phytometers succeeded in providing a standardized climate biomass response independent of local soil effects. This allowed us to factor out climate effects in local soil phytometers, establishing that nitrogen availability did not predict biomass production, while phosphorus availability exerted a strong, positive effect independent of climate. Additionally, we identified a negative relationship between biomass production and potassium and magnesium availability. Species-specific biomass responses to the environment in the climate-corrected biomass were asynchronous, demonstrating the importance of species interactions in vegetation responses to global change. Biomass production was co-limited by climatic and soil drivers, with each species experiencing its own unique set of co-limitations. Our study demonstrates the potential of phytometers for disentangling effects of climate and soil on plant biomass production and suggests an increasing role of P limitation in the temperate regions of Europe.
Measurement of iodine species and sulfuric acid using bromide chemical ionization mass spectrometers
(2021)
Iodine species are important in the marine atmosphere for oxidation and new-particle formation. Understanding iodine chemistry and iodine new-particle formation requires high time resolution, high sensitivity, and simultaneous measurements of many iodine species. Here, we describe the application of a bromide chemical ionization mass spectrometer (Br-CIMS) to this task. During the iodine oxidation experiments in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber, we have measured gas-phase iodine species and sulfuric acid using two Br-CIMS, one coupled to a Multi-scheme chemical IONization inlet (Br-MION-CIMS) and the other to a Filter Inlet for Gasses and AEROsols inlet (Br-FIGAERO-CIMS). From offline calibrations and intercomparisons with other instruments, we have quantified the sensitivities of the Br-MION-CIMS to HOI, I2, and H2SO4 and obtained detection limits of 5.8 × 106, 3.8 × 105, and 2.0 × 105 molec. cm−3, respectively, for a 2 min integration time. From binding energy calculations, we estimate the detection limit for HIO3 to be 1.2 × 105 molec. cm−3, based on an assumption of maximum sensitivity. Detection limits in the Br-FIGAERO-CIMS are around 1 order of magnitude higher than those in the Br-MION-CIMS; for example, the detection limits for HOI and HIO3 are 3.3 × 107 and 5.1 × 106 molec. cm−3, respectively. Our comparisons of the performance of the MION inlet and the FIGAERO inlet show that bromide chemical ionization mass spectrometers using either atmospheric pressure or reduced pressure interfaces are well-matched to measuring iodine species and sulfuric acid in marine environments.
Analyzing the impact of streamflow drought on hydroelectricity production: a global-scale study
(2021)
Electricity production by hydropower is negatively affected by drought. To understand and quantify risks of less than normal streamflow for hydroelectricity production (HP) at the global scale, we developed an HP model that simulates time series of monthly HP worldwide and thus enables analyzing the impact of drought on HP. The HP model is based on a new global hydropower database (GHD), containing 8,716 geo-localized plant records, and on monthly streamflow values computed by the global hydrological model WaterGAP with a spatial resolution of 0.5°. The GHD includes 44 attributes and covers 91.8% of the globally installed capacity. The HP model can reproduce HP trends, seasonality, and interannual variability that was caused by both (de)commissioning of hydropower plants and hydrological variability. It can also simulate streamflow drought and its impact on HP reasonably well. Global risk maps of HP reduction were generated for both 0.5° grid cells and countries, revealing that 67 out of the 134 countries with hydropower suffer, in 1 out of 10 years, from a reduction of more than 20% of mean annual HP and 18 countries from a reduction of more than 40%. The developed HP model enables advanced assessments of drought impacts on hydroelectricity at national to international levels.
AirCore samplers have been increasingly used to capture vertical profiles of trace gases reaching from the ground up to about 30 km, in order to validate remote sens- ing instruments and to investigate transport processes in the stratosphere. When deployed to a weather balloon, accu- rately attributing the trace gas measurements to the sampling altitudes is nontrivial, especially in the stratosphere. In this paper we present the CO-spiking experiment, which can be deployed to any AirCore on any platform in order to evalu- ate different computational altitude attribution processes and to experimentally derive the vertical resolution of the profile by injecting small volumes of signal gas at predefined GPS altitudes during sampling. We performed two CO-spiking flights with an AirCore from the Goethe University Frankfurt (GUF) deployed to a weather balloon in Traînou, France, in June 2019. The altitude retrieval based on an instantaneous pressure equilibrium assumption slightly overestimates the sampling altitudes, especially at the top of the profiles. For these two flights our altitude attribution is accurate within 250 m below 20 km. Above 20 km the positive bias becomes larger and reaches up to 1.2 km at 27 km altitude. Differences in descent velocities are shown to have a major impact on the altitude attribution bias. We parameterize the time lag between the theoretically attributed altitude and the actual CO-spike release altitude for both flights together and use it to empirically correct our AirCore altitude retrieval. Regard- ing the corrected profiles, the altitude attribution is accurate within ±120 m throughout the profile. Further investigations are needed in order to test for the scope of validity of this correction parameter regarding different ambient conditions and maximum flight altitudes. We derive the vertical resolu- tion from the CO spikes of both flights and compare it to the modeled vertical resolution. The modeled vertical resolution is too optimistic compared to the experimentally derived res- olution throughout the profile, albeit agreeing within 220 m. All our findings derived from the two CO-spiking flights are strictly bound to the GUF AirCore dimensions. The newly introduced CO-spiking experiment can be used to test differ- ent combinations of AirCore configurations and platforms in future studies.
Central and western Europe were affected by a compressional tectonic event in the Late Cretaceous, caused by the convergence of Iberia and Europe. Basement uplifts, inverted graben structures, and newly formed marginal troughs are the main expressions of crustal shortening. Although the maximum activity occurred during a short period of time between 90 and 75 Ma, the exact timing of this event is still unclear. Dating of the start and end of Late Cretaceous basin inversion gives very different results depending on the method applied. On the basis of borehole data, facies, and thickness maps, the timing of basin reorganization was reconstructed for several basins in central Europe. The obtained data point to a synchronous start of basin inversion at 95 Ma (Cenomanian), 5 Myr earlier than commonly assumed. The end of the Late Cretaceous compressional event is difficult to pinpoint in central Europe, because regional uplift and salt migration disturb the signal of shifting marginal troughs. Late Campanian to Paleogene strata deposited unconformably on inverted structures indicate slowly declining uplift rates during the latest Cretaceous. The differentiation of separate Paleogene inversion phases in central Europe does not appear possible at present.
Analysing the composition of ambient ultrafine particles (UFPs) is a challenging task due to the low mass and chemical complexity of small particles, yet it is a prerequisite for the identification of particle sources and the assessment of potential health risks. Here, we show the molecular characterization of UFPs, based on cascade impactor (Nano-MOUDI) samples that were collected at an air quality monitoring station near one of Europe's largest airports, in Frankfurt, Germany. At this station, particle-size-distribution measurements show an enhanced number concentration of particles smaller than 50 nm during airport operating hours. We sampled the lower UFP fraction (0.010–0.018, 0.018–0.032, 0.032–0.056 µm) when the air masses arrived from the airport. We developed an optimized filter extraction procedure using ultra-high-performance liquid chromatography (UHPLC) for compound separation and a heated electrospray ionization (HESI) source with an Orbitrap high-resolution mass spectrometer (HRMS) as a detector for organic compounds. A non-target screening detected ∼200 organic compounds in the UFP fraction with sample-to-blank ratios larger than 5. We identified the largest signals as homologous series of pentaerythritol esters (PEEs) and trimethylolpropane esters (TMPEs), which are base stocks of aircraft lubrication oils. We unambiguously attribute the majority of detected compounds to jet engine lubrication oils by matching retention times, high-resolution and accurate mass measurements, and comparing tandem mass spectrometry (MS2) fragmentation patterns between both ambient samples and commercially available jet oils. For each UFP stage, we created molecular fingerprints to visualize the complex chemical composition of the organic fraction and their average carbon oxidation state. These graphs underline the presence of the homologous series of PEEs and TMPEs and the appearance of jet oil additives (e.g. tricresyl phosphate, TCP). Targeted screening of TCP confirmed the absence of the harmful tri-ortho isomer, while we identified a thermal transformation product of TMPE-based lubrication oil (trimethylolpropane phosphate, TMP-P). Even though a quantitative determination of the identified compounds is limited, the presented method enables the qualitative detection of molecular markers for jet engine lubricants in UFPs and thus strongly improves the source apportionment of UFPs near airports.
Toward parametrization of precipitating shallow cumulus cloud organization via moisture variance
(2021)
The influence of the initial vertical moisture profile on precipitating shallow cumulus cloud organization in terms of the column-averaged moisture variance is investigated using large-eddy simulations. Five idealized simulations based on the Rain in Cumulus over the Ocean field experiment with different initial moisture profiles are investigated. All cases simulate precipitating shallow cumulus convection in a marine sub-tropical region under large-scale subsidence. The results show that the moisture variance is mainly generated through the interaction of the moisture flux and the moisture gradient in the gradient production term at the top of the boundary layer. The development is characterized by three regimes: initial, transition, and quasi-steady regime. During the initial regime, the moisture gradient is built up by moisture accumulation until precipitating convection starts. Within the transition regime, precipitation enables mesoscale cloud organization with enhanced convective activity and moisture fluxes. The moisture variance increases from the moist to the dry initial moisture profiles. In a following quasi-steady regime, the moisture variance is approximately preserved. Thereby, the initial moisture gradient between the average sub-cloud layer and the free atmosphere is found to be an important factor for the generation of the quasi-steady column-averaged moisture variance. The result suggests that a resolved-scale variable like the moisture gradient can be used to estimate the quasi-steady state conditions resulting from cloud organization. This finding may serve as a starting point for the parametrization of the subgrid scale cloud organization caused by precipitating shallow convection.
Non-technical summary: There has been a long history of conflicts, studies, and debate over how to both protect rivers and develop them sustainably. With a pause in new developments caused by the global pandemic, anticipated further implementation of the Paris Agreement and high-level global climate and biodiversity meetings in 2021, now is an opportune moment to consider the current trajectory of development and policy options for reconciling dams with freshwater system health. Technical summary: We calculate potential loss of free-flowing rivers (FFRs) if proposed hydropower projects are built globally. Over 260,000 km of rivers, including Amazon, Congo, Irrawaddy, and Salween mainstem rivers, would lose free-flowing status if all dams were built. We propose a set of tested and proven solutions to navigate trade-offs associated with river conservation and dam development. These solution pathways are framed within the mitigation hierarchy and include (1) avoidance through either formal river protection or through exploration of alternative development options; (2) minimization of impacts through strategic or system-scale planning or re-regulation of downstream flows; (3) restoration of rivers through dam removal; and (4) mitigation of dam impacts through biodiversity offsets that include restoration and protection of FFRs. A series of examples illustrate how avoiding or reducing impacts on rivers is possible – particularly when implemented at a system scale – and can be achieved while maintaining or expanding benefits for climate resilience, water, food, and energy security. Social media summary: Policy solutions and development pathways exist to navigate trade-offs to meet climate resilience, water, food, and energy security goals while safeguarding FFRs.
Global water models (GWMs) simulate the terrestrial water cycle, on the global scale, and are used to assess the impacts of climate change on freshwater systems. GWMs are developed within different modeling frameworks and consider different underlying hydrological processes, leading to varied model structures. Furthermore, the equations used to describe various processes take different forms and are generally accessible only from within the individual model codes. These factors have hindered a holistic and detailed understanding of how different models operate, yet such an understanding is crucial for explaining the results of model evaluation studies, understanding inter-model differences in their simulations, and identifying areas for future model development. This study provides a comprehensive overview of how state-of-the-art GWMs are designed. We analyze water storage compartments, water flows, and human water use sectors included in 16 GWMs that provide simulations for the Inter-Sectoral Impact Model Intercomparison Project phase 2b (ISIMIP2b). We develop a standard writing style for the model equations to further enhance model improvement, intercomparison, and communication. In this study, WaterGAP2 used the highest number of water storage compartments, 11, and CWatM used 10 compartments. Seven models used six compartments, while three models (JULES-W1, Mac-PDM.20, and VIC) used the lowest number, three compartments. WaterGAP2 simulates five human water use sectors, while four models (CLM4.5, CLM5.0, LPJmL, and MPIHM) simulate only water used by humans for the irrigation sector. We conclude that even though hydrologic processes are often based on similar equations, in the end, these equations have been adjusted or have used different values for specific parameters or specific variables. Our results highlight that the predictive uncertainty of GWMs can be reduced through improvements of the existing hydrologic processes, implementation of new processes in the models, and high-quality input data.
Global water models (GWMs) simulate the terrestrial water cycle on the global scale and are used to assess the impacts of climate change on freshwater systems. GWMs are developed within different modelling frameworks and consider different underlying hydrological processes, leading to varied model structures. Furthermore, the equations used to describe various processes take different forms and are generally accessible only from within the individual model codes. These factors have hindered a holistic and detailed understanding of how different models operate, yet such an understanding is crucial for explaining the results of model evaluation studies, understanding inter-model differences in their simulations, and identifying areas for future model development. This study provides a comprehensive overview of how 16 state-of-the-art GWMs are designed. We analyse water storage compartments, water flows, and human water use sectors included in models that provide simulations for the Inter-Sectoral Impact Model Intercomparison Project phase 2b (ISIMIP2b). We develop a standard writing style for the model equations to enhance model intercomparison, improvement, and communication. In this study, WaterGAP2 used the highest number of water storage compartments, 11, and CWatM used 10 compartments. Six models used six compartments, while four models (DBH, JULES-W1, Mac-PDM.20, and VIC) used the lowest number, three compartments. WaterGAP2 simulates five human water use sectors, while four models (CLM4.5, CLM5.0, LPJmL, and MPI-HM) simulate only water for the irrigation sector. We conclude that, even though hydrological processes are often based on similar equations for various processes, in the end these equations have been adjusted or models have used different values for specific parameters or specific variables. The similarities and differences found among the models analysed in this study are expected to enable us to reduce the uncertainty in multi-model ensembles, improve existing hydrological processes, and integrate new processes.
In the last decade, the Climate Limited-area Modeling (CLM) Community has contributed to the Coordinated Regional Climate Downscaling Experiment (CORDEX) with an extensive set of regional climate simulations. Using several versions of the COSMO-CLM community model, ERA-Interim reanalysis and eight Global Climate Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) were dynamically downscaled with horizontal grid spacings of 0.44◦(∼50 km), 0.22◦ (∼25 km) and 0.11◦ (∼12 km) over the CORDEX domains Europe, South Asia, East Asia, Australasia and Africa. This major effort resulted in 80 regional climate simulations publicly available through the Earth System Grid Federation (ESGF) web portals for use in impact studies and climate scenario assessments. Here we review the production of these simulations and assess their results in terms of mean near-surface temperature and precipitation to aid the future design of the COSMO-CLM model simulations. It is found that a domain-specific parameter tuning is beneficial, while increasing horizontal model resolution (from 50 to 25 or 12 km grid spacing) alone does not always improve the performance of the simulation. Moreover, the COSMO-CLM performance depends on the driving data. This is generally more important than the dependence on horizontal resolution, model version and configuration. Our results emphasize the importance of performing regional climate projections in a coordinated way, where guidance from both the global (GCM) and regional (RCM) climate modelling communities is needed to increase the reliability of the GCM-RCM modelling chain.
In the last decade, the Climate Limited-area Modeling Community (CLM-Community) has contributed to the Coordinated Regional Climate Downscaling Experiment (CORDEX) with an extensive set of regional climate simulations. Using several versions of the COSMO-CLM-Community model, ERA-Interim reanalysis and eight global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) were dynamically downscaled with horizontal grid spacings of 0.44∘ (∼ 50 km), 0.22∘ (∼ 25 km), and 0.11∘ (∼ 12 km) over the CORDEX domains Europe, South Asia, East Asia, Australasia, and Africa. This major effort resulted in 80 regional climate simulations publicly available through the Earth System Grid Federation (ESGF) web portals for use in impact studies and climate scenario assessments. Here we review the production of these simulations and assess their results in terms of mean near-surface temperature and precipitation to aid the future design of the COSMO-CLM model simulations. It is found that a domain-specific parameter tuning is beneficial, while increasing horizontal model resolution (from 50 to 25 or 12 km grid spacing) alone does not always improve the performance of the simulation. Moreover, the COSMO-CLM performance depends on the driving data. This is generally more important than the dependence on horizontal resolution, model version, and configuration. Our results emphasize the importance of performing regional climate projections in a coordinated way, where guidance from both the global (GCM) and regional (RCM) climate modeling communities is needed to increase the reliability of the GCM–RCM modeling chain.
In the Central German Uplands, Fagus sylvatica and Picea abies have been particularly affected by climate change. With the establishment of beech forests about 3000 years ago and pure spruce stands 500 years ago, they might be regarded as ‘neophytes’ in the Hessian forests. Palaeoecological investigations at wetland sites in the low mountain ranges and intramontane basins point to an asynchronous vegetation evolution in a comparatively small but heterogenous region. On the other hand, palynological data prove that sustainably managed woodlands with high proportions of Tilia have been persisting for several millennia, before the spread of beech took place as a result of a cooler and wetter climate and changes in land management. In view of increasingly warmer and drier conditions, Tilia cordata appears especially qualified to be an important silvicultural constituent of the future, not only due to its tolerance towards drought, but also its resistance to browsing, and the ability to reproduce vegetatively. Forest managers should be encouraged to actively promote the return to more stress-tolerant lime-dominated woodlands, similar to those that existed in the Subboreal chronozone.
The evolution and interrelationships of carnivorous squamates (mosasaurs, snakes, monitor lizards, Gila Monsters) are a contentious part of reptile systematics and go to the heart of conflict between morphological and molecular data in inferring evolutionary history. One of the best-preserved fossils in this motley grouping is “Saniwa” feisti Stritzke, 1983, represented by complete skeletons from the early-middle Eocene of Messel, Germany. We re-describe it on the basis of superficial examination, stereoradiography, and high-resolution X-ray computed tomography of new and published specimens. The scalation of the lizard is unique, consisting of small, keeled scales on the head (including a row of enlarged medial supraorbitals) and large, rhomboidal, keeled scales (invested by osteoderms) that covered the rest of the body. Two paired longitudinal rows of enlarged scales ran down the neck. The head was laterally compressed and box-shaped due to the presence of a strong canthal-temporal ridge; the limbs and tail were very long. Notable osteological features include: a toothed, strap-like vomer; septomaxilla with a long posterior process; palpebral with a long posterolateral process; a lacrimal boss and a single lacrimal foramen; a well-developed cultriform process of the parabasisphenoid; two hypoglossal (XII) foramina in addition to the vagus; a lack of resorption pits for replacement teeth; and possibly the presence of more than one wave of developing replacement teeth per locus. There are no osteological modifications suggestive of an intramandibular hinge, but postmortem displacement of the angular-prearticular-surangular complex in multiple specimens suggests that there might have been some degree of mobility in the lower jaw based on soft-tissue modifications. Using phylogenetic analyses on a data-set comprising 473 morphological characters and 46 DNA loci, we infer that a monophyletic Palaeovaranidae Georgalis, 2017, including Eosaniwa Haubold, 1977, lies on the stem of Varanidae Merrem, 1820, basal to various Cretaceous Mongolian taxa. We transfer feisti to the new genus Paranecrosaurus n. gen. Analysis of gut contents reveals only the second known specimen of the cryptozoic lizard Cryptolacerta hassiaca Müller, Hipsley, Head, Kardjilov, Hilger, Wuttke & Reisz, 2011, confirming a diet that was at least partly carnivorous; the preservation of the teeth of C. hassiaca suggests that the gastric physiology of Paranecrosaurus feisti (Stritzke, 1983) n. comb. had high acidity but low enzyme activity. Based on the foregoing and linear discriminant function analysis, we reconstruct P. feisti n. comb., as a powerful, widely roaming, faunivorous-carnivorous stem monitor lizard with a sensitive snout. If the molecular phylogeny of anguimorphs is correct, then many of the features shared by Helodermatidae Gray, 1837 and Varanidae must have arisen convergently, partly associated with diet. In that case, a reconciliation of morphological and molecular data would require the discovery of equally primitive fossils on the helodermatid stem.
We combined biostratigraphical analyses, archaeological surveys, and Glacial Isostatic Adjustment (GIA) models to provide new insights into the relative sea-level evolution in the northeastern Aegean Sea (eastern Mediterranean). In this area, characterized by a very complex tectonic pattern, we produced a new typology of sea-level index point, based on the foraminiferal associations found in transgressive marine facies. Our results agree with the sea-level history previously produced in this region, therefore confirming the validity of this new type of index point. The expanded dataset presented in this paper further demonstrates a continuous Holocene RSL rise in this portion of the Aegean Sea. Comparing the new RSL record with the available geophysical predictions of sea-level evolution indicates that the crustal subsidence of the Samothraki Plateau and the North Aegean Trough played a major role in controlling millennial-scale sea-level evolution in the area. This major subsidence rate needs to be taken into account in the preparation of local future scenarios of sea-level rise in the coming decades.
Acesta excavata (Fabricius, 1779) is a slow growing bivalve from the Limidae family and is often found associated with cold-water coral reefs along the European continental margin. Here we present the compositional variability of frequently used proxy elemental ratios (Mg/ Ca, Sr/Ca, Na/Ca) measured by laser-ablation mass spectrometry (LA-ICP-MS) and com- pare it to in-situ recorded instrumental seawater parameters such as temperature and salin- ity. Shell Mg/Ca measured in the fibrous calcitic shell section was overall not correlated with seawater temperature or salinity; however, some samples show significant correlations with temperature with a sensitivity that was found to be unusually high in comparison to other marine organisms. Mg/Ca and Sr/Ca measured in the fibrous calcitic shell section display significant negative correlations with the linear extension rate of the shell, which indicates strong vital effects in these bivalves. Multiple linear regression analysis indicates that up to 79% of elemental variability is explicable with temperature and salinity as independent pre- dictor values. Yet, the overall results clearly show that the application of Element/Ca (E/Ca) ratios in these bivalves to reconstruct past changes in temperature and salinity is likely to be complicated due to strong vital effects and the effects of organic material embedded in the shell. Therefore, we suggest to apply additional techniques, such as clumped isotopes, in order to exactly determine and quantify the underlying vital effects and possibly account for these. We found differences in the chemical composition between the two calcitic shell lay- ers that are possibly explainable through differences of the crystal morphology. Sr/Ca ratios also appear to be partly controlled by the amount of magnesium, because the small magne- sium ions bend the crystal lattice which increases the space for strontium incorporation. Oxi- dative cleaning with H2O2 did not significantly change the Mg/Ca and Sr/Ca composition of the shell. Na/Ca ratios decreased after the oxidative cleaning, which is most likely a leaching effect and not caused by the removal of organic matter.
Hyrrokkin sarcophaga is a parasitic foraminifera that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Desmophyllum pertusum (formerly known as Lophelia pertusa). Here, we present measurements of the trace element and isotopic composition of these parasitic foraminifera, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe microanalysis (EPMA) and mass spectrometry (gas-source MS and inductively-coupled-plasma MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr / Ca ratios are 1.1 mmol mol−1 higher in H. sarcophaga that infest D. pertusum, which could be an indication that dissolved host carbonate material is utilized in shell calcification, given that the aragonite of D. pertusum has a naturally higher Sr concentration compared to the calcite of A. excavata. Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on D. pertusum, which might be caused by the direct uptake of the host's carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn / Ca ratios in foraminifera that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifera, these data also indicate that the geochemistry of this parasitic foraminifera is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr / Ca, Mn / Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.
Hyrrokkin sarcophaga is a parasitic foraminifer that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Lophelia pertusa. Here, we present measurements of the elemental and isotopic composition of this parasitic foraminifer for the first time, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe micro analysis (EPMA) and mass spectrometry (MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr/Ca ratios are 1.1 mmol mol-1 higher in H. sarcophaga that infest L. pertusa, which could be an indication that dissolved host carbonate material is utilised in shell calcification, given that the aragonite of L. pertusa has a naturally higher Sr concentration compared to the calcite of A. excavata.Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on20 L. pertusa, which might be caused by the direct uptake of the host’s carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn/Ca ratios in foraminifers that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifer, these data also indicate that the geochemistry of this parasitic foraminifer is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr/Ca, Mn/Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.
Droughts are anticipated to intensify in many parts of the world due to climate change. However, the issue of drought definition, namely the diversity of drought indices, makes it difficult to compare drought assessments. This issue is widely known, but its relative importance has never been quantitatively evaluated in comparison to other sources of uncertainty. Here, encompassing three drought categories (meteorological, agricultural, and hydrological droughts) with four temporal scales of interest, we evaluated changes in the drought frequency using multi-model and multi-scenario simulations to identify areas where the definition issue could result in pronounced uncertainties and to what extent. We investigated the disagreement in the signs of changes between drought definitions and decomposed the variance into four main factors: drought definitions, greenhouse gas concentration scenarios, global climate models, and global water models, as well as their interactions. The results show that models were the primary sources of variance over 82% of the global land area. On the other hand, the drought definition was the dominant source of variance in the remaining 17%, especially in parts of northern high-latitudes. Our results highlight specific regions where differences in drought definitions result in a large spread among projections, including areas showing opposite signs of significant changes. At a global scale, 7% of the variance resulted independently from the definition issue, and that value increased to 44% when 1st and 2nd order interactions were considered. The quantitative results suggest that by clarifying hydrological processes or sectors of interest, one could avoid these uncertainties in drought assessments to obtain a clearer picture of future drought change.
Constraining the architecture of complex 3D volcanic plumbing systems within active rifts, and their impact on rift processes, is critical for examining the interplay between faulting, magmatism and magmatic fluids in developing rift segments. The Natron basin of the East African Rift System provides an ideal location to study these processes, owing to its recent magmatic-tectonic activity and ongoing active carbonatite volcanism at Oldoinyo Lengai. Here, we report seismicity and fault plane solutions from a 10-month temporary seismic network spanning Oldoinyo Lengai, Naibor Soito volcanic field and Gelai volcano. We locate 6827 earthquakes with ML -0.85 to 3.6, which are related to previous and ongoing magmatic and volcanic activity in the region, as well as regional tectonic extension. We observe seismicity down to ~17 km depth north and south of Oldoinyo Lengai and shallow seismicity (3 - 10 km) beneath Gelai, including two swarms. The deepest seismicity (~down to 20 km) occurs above a previously imaged magma body below Naibor Soito. These seismicity patterns reveal a detailed image of a complex volcanic plumbing system, supporting potential lateral and vertical connections between shallow- and deep-seated magmas, where fluid and melt transport to the surface is facilitated by intrusion of dikes and sills. Focal mechanisms vary spatially. T-axis trends reveal dominantly WNW-ESE extension near Gelai, while strike-slip mechanisms and a radial trend in P-axes are observed in the vicinity of Oldoinyo Lengai. These data support local variations in the state of stress, resulting from a combination of volcanic edifice loading and magma-driven stress changes imposed on a regional extensional stress field. Our results indicate that the southern Natron basin is a segmented rift system, in which fluids preferentially percolate vertically and laterally in a region where strain transfers from a border fault to a developing magmatic rift segment.
Extreme convective precipitation is expected to increase with global warming. However, the rate of increase and the understanding of contributing processes remain highly uncertain. We investigated characteristics of convective rain cells like area, intensity, and lifetime as simulated by a convection-permitting climate model in the area of Germany under historical (1976–2005) and future (end-of-century, RCP8.5 scenario) conditions. To this end, a tracking algorithm was applied to 5-min precipitation output. While the number of convective cells is virtually similar under historical and future conditions, there are more intense and larger cells in the future. This yields an increase in hourly precipitation extremes, although mean precipitation decreases. The relative change in the frequency distributions of area, intensity, and precipitation sum per cell is highest for the most extreme percentiles, suggesting that extreme events intensify the most. Furthermore, we investigated the temperature and moisture scaling of cell characteristics. The temperature scaling drops off at high temperatures, with a shift in drop-off towards higher temperatures in the future, allowing for higher peak values. In contrast, dew point temperature scaling shows consistent rates across the whole dew point range. Cell characteristics scale at varying rates, either below (mean intensity), at about (maximum intensity and area), or above (precipitation sum) the Clausius–Clapeyron rate. Thus, the widely investigated extreme precipitation scaling at fixed locations is a complex product of the scaling of different cell characteristics. The dew point scaling rates and absolute values of the scaling curves in historical and future conditions are closest for the highest percentiles. Therefore, near-surface humidity provides a good predictor for the upper limit of for example, maximum intensity and total precipitation of individual convective cells. However, the frequency distribution of the number of cells depending on dew point temperature changes in the future, preventing statistical inference of extreme precipitation from near-surface humidity.
Drought is understood as both a lack of water (i.e., a deficit compared to demand) and a temporal anomaly in one or more components of the hydrological cycle. Most drought indices, however, only consider the anomaly aspect, i.e., how unusual the condition is. In this paper, we present two drought hazard indices that reflect both the deficit and anomaly aspects. The soil moisture deficit anomaly index, SMDAI, is based on the drought severity index, DSI (Cammalleri et al., 2016), but is computed in a more straightforward way that does not require the definition of a mapping function. We propose a new indicator of drought hazard for water supply from rivers, the streamflow deficit anomaly index, QDAI, which takes into account the surface water demand of humans and freshwater biota. Both indices are computed and analyzed at the global scale, with a spatial resolution of roughly 50 km, for the period 1981–2010, using monthly time series of variables computed by the global water resources and the model WaterGAP 2.2d. We found that the SMDAI and QDAI values are broadly similar to values of purely anomaly-based indices. However, the deficit anomaly indices provide more differentiated spatial and temporal patterns that help to distinguish the degree and nature of the actual drought hazard to vegetation health or the water supply. QDAI can be made relevant for stakeholders with different perceptions about the importance of ecosystem protection, by adapting the approach for computing the amount of water that is required to remain in the river for the well-being of the river ecosystem. Both deficit anomaly indices are well suited for inclusion in local or global drought risk studies.
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 (Chemical Lagrangian Model of the Stratosphere), driven by reanalysis winds and total diabatic heating rates. ERA5-based results are compared to results based on the preceding ERA-Interim reanalysis. Our results show a significantly slower BDC for ERA5 than for ERA-Interim, manifesting in weaker diabatic heating rates and higher age of air. In the tropical lower stratosphere, heating rates are 30 %–40 % weaker in ERA5, likely correcting a bias in ERA-Interim. At 20 km and in the Northern Hemisphere (NH) stratosphere, ERA5 age values are around the upper margin of the uncertainty range from historical tracer observations, indicating a somewhat slow–biased BDC. The age trend in ERA5 over the 1989–2018 period is negative throughout the stratosphere, as climate models predict in response to global warming. However, the age decrease is not linear but steplike, potentially caused by multi-annual variability or changes in the observations included in the assimilation. During the 2002–2012 period, the ERA5 age shows a similar hemispheric dipole trend pattern as ERA-Interim, with age increasing in the NH and decreasing in the Southern Hemisphere (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 in both reanalyses, whereas the deep branch accelerates in ERA5 and decelerates in ERA-Interim.
Role of the tropical atlantic for the interhemispheric heat transport during the last deglaciation
(2021)
Abstract
During the last deglaciation abrupt millennial-scale perturbations of the Atlantic Meridional Overturning Circulation massively altered the interhemispheric heat distribution affecting, for example, continental ice volume and hydroclimate. If and how the related cross-equatorial heat transport was controlled by the interplay between the southward-flowing Brazil Current (BC) and northward-flowing North Brazil Current (NBC) remains controversial. To assess the role of tropical heat transport during the last deglaciation, we obtained a high-resolution foraminiferal Mg/Ca-based sea surface temperature (SST) record from the BC domain at 21.5°S. The data reveal a yet undocumented warming of at least 4.6°C of the BC during Heinrich Stadial 1 at ∼16 ka indicating massive oceanic heat accumulation in the tropical South Atlantic. Simultaneously, a strongly diminished NBC prevented the release of this excess heat into the northern tropics. The observed magnitude of heat accumulation substantially exceeds numerical model simulations, stressing the need to further scrutinize atmospheric and oceanic heat transport during extreme climatic events.
Plain Language Summary
The Atlantic overturning circulation underwent abrupt millennial-scale perturbations. Such phases of sluggish oceanic circulation resulted in a substantial reduction of northward heat transport. As a consequence, substantial cooling occurred in the Northern Hemisphere and warming occurred in the Southern Hemisphere with severe effects on tropical precipitation. The distribution of heat within the western tropical Atlantic is accomplished by the southward-flowing BC and the northward-flowing NBC. By reconstructing SSTs for the interval between 20,000 and 10,000 yr before present, we assess the role of both currents in the interhemispheric heat transport during weak Atlantic overturning. We found that a sluggish overturning circulation resulted in anomalous southward heat transport by the BC in concert with a weak NBC, which lead to a yet undocumented warming of at least 4.6°C in the western tropical South Atlantic. This warming significantly exceeds reconstructions based on numerical simulations. This points to the need to further improve our understanding of changes in the cross-equatorial oceanic and atmospheric heat transport in response to rapid changes in ocean circulation, in particular as a significant weakening of the Atlantic overturning circulation is predicted in the wake of anthropogenic climate change.
A quantitative analysis of any environment older than the instrumental record relies on proxies. Uncertainties associated with proxy reconstructions are often underestimated, which can lead to artificial conflict between different proxies, and between data and models. In this paper, using ordinary least squares linear regression as a common example, we describe a simple, robust and generalizable method for quantifying uncertainty in proxy reconstructions. We highlight the primary controls on the magnitude of uncertainty, and compare this simple estimate to equivalent estimates from Bayesian, nonparametric and fiducial statistical frameworks. We discuss when it may be possible to reduce uncertainties, and conclude that the unexplained variance in the calibration must always feature in the uncertainty in the reconstruction. This directs future research toward explaining as much of the variance in the calibration data as possible. We also advocate for a “data-forward” approach, that clearly decouples the presentation of proxy data from plausible environmental inferences.
National Greenhouse Gas Inventories (GHGI) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGI. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emissions Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high Global Warming Potentials (GWPs) and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions in the since 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009–2012 shows a drop of 35%, indicating progress toward the target of a 79% decrease in sales by 2030. The total InTEM HFC emission estimates (2008–2018) are on average 73 (62–83)% of, or 4.3 (2.7–5.9) Tg CO2-eq yr−1 lower than, the total HFC emission estimates from the UK GHGI inventory. There are also significant discrepancies between the two estimates for the individual HFCs.
National greenhouse gas inventories (GHGIs) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGIs. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emission Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high global warming potentials (GWPs), and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication, its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions from 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009–2012 shows a drop of 35 %, indicating progress toward the target of a 79 % decrease in sales by 2030. The total InTEM HFC emission estimates (2008–2018) are on average 73 (62–83) % of, or 4.3 (2.7–5.9) Tg CO2-eq yr−1 lower than, the total HFC emission estimates from the UK GHGI. There are also significant discrepancies between the two estimates for the individual HFCs.
The Global South is facing severe challenges in ensuring livelihood security due to climate change impacts, environmental degradation and population growth as well as changing lifestyles. These complex problems cannot be solely solved by single scientific disciplines – they require transdisciplinary research (TDR). Stakeholders from civil society, the corporate sector, government and science need to pool their knowledge to find solutions for sustainable transformations. In Namibia, we have been involved in TDR projects on water supply, and sanitation services as well as livestock management in rangeland systems. In this paper, we review two TDR projects that differ in multiple ways and hence allow us to carve out structural differences and critically discuss research outcomes, lessons learned and the challenge of North–South collaborations. Our review builds upon published and unpublished project documents as well as expert interviews with Namibian and German researchers who were involved in the projects. Our results show that TDR can be put into practice in different ways, depending on the research focus and the period available. The TDR phases of problem framing, inter- and transdisciplinary integration were implemented with different tools and foci points. We discuss the role of project length and funding conditions for project success and outcome generation. In addition, we critically consider the role of Namibian and German researchers in these international collaborations. The conclusions we draw touch upon the points of preparatory research funding, the equal acknowledgement of Global South contributions to joint research projects and the explicit handling of TDR components in project work. Significance: • The current social-ecological challenges are complex and require TDR as a mode of knowledge coproduction, particularly in a development context. • Inter- and transdisciplinary integration are critical processes for a project to be successful and require the allocation of adequate time and monetary resources. • Longer-term projects with a funded preparatory research phase constitute a structural model for TDR as project outcomes can evolve over time. • Global South researchers carry a hidden burden in international collaborations that has to be adequately acknowledged upfront in project planning and final products.
Ob wir bei der Erwärmung eher in Richtung plus 2 Grad oder eher in Richtung plus 5 Grad steuern, entscheidet sich zu einem nicht unbedeutenden Teil über den Meeren. Dort beschatten niedrige, flache, sehr großflächige Wolkenschichten die darunterliegende Wasseroberfläche und sorgen so für Abkühlung. Auch in Zukunft noch?
The Alpine orogeny is characterized by tectonic sequences of subduction and collision accompanied by break-off events and possibly preceded by a flip of subduction polarity. The tectonic evolution of the transition to the Eastern Alps has thus been under debate. The dense SWATH-D seismic network as a complementary experiment to the AlpArray seismic network provides unprecedented lateral resolution to address this ongoing discussion. We analyze the shear-wave splitting of this data set including stations of the AlpArray backbone in the region to obtain new insights into the deformation at depth from seismic anisotropy. Previous studies indicate two-layer anisotropy in the Eastern Alps. This is supported by the azimuthal pattern of the measured fast axis direction across all analyzed stations. However, the temporary character of the deployment requires a joint analysis of multiple stations to increase the number of events adding complementary information of the anisotropic properties of the mantle. We, therefore, perform a cluster analysis based on a correlation of energy tensors between all stations. The energy tensors are assembled from the remaining transverse energy after the trial correction of the splitting effect from two consecutive anisotropic layers. This leads to two main groups of different two-layer properties, separated approximately at 13°E. We identify a layer with a constant fast axis direction (measured clockwise with respect to north) of about 60° over the whole area, with a possible dip from west to east. The lower layer in the west shows N–S fast direction and the upper layer in the east shows a fast axis of about 115°. We propose two likely scenarios, both accompanied by a slab break-off in the eastern part. The continuous layer can either be interpreted as frozen-in anisotropy with a lithospheric origin or as an asthenospheric flow evading the retreat of the European slab that would precede the break-off event. In both scenarios, the upper layer in the east is a result of a flow through the gap formed in the slab break-off. The N–S direction can be interpreted as an asthenospheric flow driven by the retreating European slab but might also result from a deep-reaching fault-related anisotropy.
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.
Deformation in the upper mantle is localized in shear zones. In order to localize strain, weakening has to occur, which can be achieved by a reduction in grain size. In order for grains to remain small and preserve shear zones, phases have to mix. Phase mixing leads to dragging or pinning of grain boundaries which slows down or halts grain growth. Multiple phase mixing processes have been suggested to be important during shear zone evolution. The importance of a phase mixing process depends on the geodynamic setting. This study presents detailed microstructural analysis of spinel bearing shear zones from the Erro-Tobbio peridotite (Italy) that formed during pre-alpine rifting. The first stage of deformation occurred under melt-free conditions, during which clinopyroxene and olivine porphyroclasts dynamically recrystallized. With ongoing extension, silica-undersaturated melt percolated through the shear zones and reacted with the clinopyroxene neoblasts, forming olivine–clinopyroxene layers. Furthermore, the melt reacted with orthopyroxene porphyroclasts, forming fine-grained polymineralic layers (ultramylonites) adjacent to the porphyroclasts. Strain rates in these layers are estimated to be about an order of magnitude faster than within the olivine-rich matrix. This study demonstrates the importance of melt-rock reactions for grain size reduction, phase mixing and strain localization in these shear zones.
In this study, we determine spectral characteristics and amplitude decays of wind turbine induced seismic signals in the far field of a wind farm (WF) close to Uettingen/Germany. Average power spectral densities (PSD) are calculated from 10 min time segments extracted from (up to) 6-months of continuous recordings at 19 seismic stations, positioned along an 8 km profile starting from the WF. We identify 7 distinct PSD peaks in the frequency range between 1 Hz and 8 Hz that can be observed to at least 4 km distance; lower-frequency peaks are detectable up to the end of the profile. At distances between 300 m and 4 km the PSD amplitude decay can be described by a power law with exponent b. The measured b-values exhibit a linear frequency dependence and range from b = 0.39 at 1.14 Hz to b = 3.93 at 7.6 Hz. In a second step, the seismic radiation and amplitude decays are modeled using an analytical approach which approximates the surface-wave field. Since we observe temporally varying phase differences between seismograms recorded directly at the base of the individual wind turbines (WTs), source-signal phase information is included in the modeling approach. We show that phase differences between source signals have significant effects on the seismic radiation pattern and amplitude decays. Therefore, we develop a phase-shift-elimination-method to handle the challenge of choosing representative source characteristics as an input for the modeling. To optimize the fitting of modeled and observed amplitude decay curves, we perform a grid search to constrain the two model parameters, i.e., the seismic shear wave velocity and quality factor. The comparison of modeled and observed amplitude decays for the 7 prominent frequencies shows very good agreement and allows to constrain shear velocities and quality factors for a two-layer model of the subsurface. The approach is generalized to predict amplitude decays and radiation patterns for WFs of arbitrary geometry.
In this study, we determine spectral characteristics and amplitude decays of wind turbine induced seismic signals in the far field of a wind farm (WF) close to Uettingen, Germany. Average power spectral densities (PSDs) are calculated from 10 min time segments extracted from (up to) 6 months of continuous recordings at 19 seismic stations, positioned along an 8 km profile starting from the WF. We identify seven distinct PSD peaks in the frequency range between 1 and 8 Hz that can be observed to at least 4 km distance; lower-frequency peaks are detectable up to the end of the profile. At distances between 300 m and 4 km the PSD amplitude decay can be described by a power law with exponent b. The measured b values exhibit a linear frequency dependence and range from b=0.39 at 1.14 Hz to b=3.93 at 7.6 Hz. In a second step, the seismic radiation and amplitude decays are modeled using an analytical approach that approximates the surface wave field. Since we observe temporally varying phase differences between seismograms recorded directly at the base of the individual wind turbines (WTs), source signal phase information is included in the modeling approach. We show that phase differences between source signals have significant effects on the seismic radiation pattern and amplitude decays. Therefore, we develop a phase shift elimination method to handle the challenge of choosing representative source characteristics as an input for the modeling. To optimize the fitting of modeled and observed amplitude decay curves, we perform a grid search to constrain the two model parameters, i.e., the seismic shear wave velocity and quality factor. The comparison of modeled and observed amplitude decays for the seven prominent frequencies shows very good agreement and allows the constraint of shear velocities and quality factors for a two-layer model of the subsurface. The approach is generalized to predict amplitude decays and radiation patterns for WFs of arbitrary geometry.
The abyssal seafloor is a mosaic of highly diverse habitats that represent the least known marine ecosystems on Earth. Some regions enriched in natural resources, such as polymetallic nodules in the Clarion-Clipperton Zone (CCZ), attract much interest because of their huge commercial potential. Since nodule mining will be destructive, baseline data are necessary to measure its impact on benthic communities. Hence, we conducted an environmental DNA and RNA metabarcoding survey of CCZ biodiversity targeting microbial and meiofaunal eukaryotes that are the least known component of the deep-sea benthos. We analyzed two 18S rRNA gene regions targeting eukaryotes with a focus on Foraminifera (37F) and metazoans (V1V2), sequenced from 310 surface-sediment samples from the CCZ and other abyssal regions. Our results confirm huge unknown deep-sea biodiversity. Over 60% of benthic foraminiferal and almost a third of eukaryotic operational taxonomic units (OTUs) could not be assigned to a known taxon. Benthic Foraminifera are more common in CCZ samples than metazoans and dominated by clades that are only known from environmental surveys. The most striking results are the uniqueness of CCZ areas, both datasets being characterized by a high number of OTUs exclusive to the CCZ, as well as greater beta diversity compared to other abyssal regions. The alpha diversity in the CCZ is high and correlated with water depth and terrain complexity. Topography was important at a local scale, with communities at CCZ stations located in depressions more diverse and heterogeneous than those located on slopes. This could result from eDNA accumulation, justifying the interim use of eRNA for more accurate biomonitoring surveys. Our descriptions not only support previous findings and consolidate our general understanding of deep-sea ecosystems, but also provide a data resource inviting further taxon-specific and large-scale modeling studies. We foresee that metabarcoding will be useful for deep-sea biomonitoring efforts to consider the diversity of small taxa, but it must be validated based on ground truthing data or experimental studies.
Production and use of many synthetic halogenated trace gases are regulated internationally due to their contribution to stratospheric ozone depletion or climate change. In many applications they have been replaced by shorter-lived compounds, which have become measurable in the atmosphere as emissions increased. Non-target monitoring of trace gases rather than targeted measurements of well-known substances is needed to keep up with such changes in the atmospheric composition. We regularly deploy gas chromatography (GC) coupled to time-of-flight mass spectrometry (TOF-MS) for analysis of flask air samples and in situ measurements at the Taunus Observatory, a site in central Germany. TOF-MS acquires data over a continuous mass range that enables a retrospective analysis of the dataset, which can be considered a type of digital air archive. This archive can be used if new substances come into use and their mass spectrometric fingerprint is identified. However, quantifying new replacement halocarbons can be challenging, as mole fractions are generally low, requiring high measurement precision and low detection limits. In addition, calibration can be demanding, as calibration gases may not contain sufficiently high amounts of newly measured substances or the amounts in the calibration gas may have not been quantified. This paper presents an indirect data evaluation approach for TOF-MS data, where the calibration is linked to another compound which could be quantified in the calibration gas. We also present an approach to evaluate the quality of the indirect calibration method, select periods of stable instrument performance and determine well suited reference compounds. The method is applied to three short-lived synthetic halocarbons: HFO-1234yf, HFO-1234ze(E), and HCFO-1233zd(E). They represent replacements for longer-lived hydrofluorocarbons (HFCs) and exhibit increasing mole fractions in the atmosphere.
The indirectly calibrated results are compared to directly calibrated measurements using data from TOF-MS canister sample analysis and TOF-MS in situ measurements, which are available for some periods of our dataset. The application of the indirect calibration method on several test cases can result in uncertainties of around 6 % to 11 %. For hydro(chloro-)fluoroolefines (denoted H(C)FOs), uncertainties up to 23 % are achieved. The indirectly calculated mole fractions of the investigated H(C)FOs at Taunus Observatory range between measured mole fractions at urban Dübendorf and Jungfraujoch stations in Switzerland.
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.
Late Paleozoic (Variscan) magmatism is widespread in Central Europe. The Lusatian Block is located in the NE Bohemian Massif and it is part of the Saxothuringian Zone of the Variscan orogen. It is bordered by two major NW-trending shear zones, the Intra-Sudetic Fault Zone towards NE and the Elbe Fault Zone towards SW. The scarce Variscan igneous rocks of the Lusatian Block are situated close to these faults. We investigated 19 samples from Variscan plutonic and volcanic rocks of the Lusatian Block, considering all petrological varieties (biotite-bearing granites from the Koenigshain and Stolpen plutons, amphibole-bearing granites from three boreholes, several volcanic dykes, and two volcanites from the intramontane Weissig basin). We applied whole-rock geochemistry (18 samples) and zircon evaporation dating (19 samples). From the evaporation data, we selected six representative samples for additional zircon SHRIMP and CA–ID–TIMS dating. For the Koenigshain pluton, possible protoliths were identified using whole-rock Nd-isotopes, and zircon Hf- and O-isotopes. The new age data allow a subdivision of Variscan igneous rocks in the Lusatian Block into two distinct magmatic episodes. The spatial relation of the two age groups to either the Elbe Fault Zone (298–299 Ma) or the Intra-Sudetic Fault Zone (312–313 Ma) together with reports on the fault-bound character of the dated intrusions suggests an interpretation as two major post-collisional faulting episodes. This assumption of two distinct magmatic periods is confirmed by a compilation of recently published zircon U–Pb CA–ID–TIMS data on further Variscan igneous rocks from the Saxothuringian Zone. New geochemical data allow us to exclude a dominant sedimentary protolith for the Koenigshain pluton as supposed by previous investigations. This conclusion is mainly based on new O- and Hf-isotope data on zircon and the scarcity of inherited zircons. Instead, acid or intermediate igneous rocks are supposed as the main source for these I-type granitoids from the Koenigshain pluton.
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.
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.
Chondrules are thought to play a crucial role in planet formation, but the mechanisms leading to their formation are still a matter of unresolved discussion. So far, experiments designed to understand chondrule formation conditions have been carried out only under the influence of terrestrial gravity. In order to introduce more realistic conditions, we developed a chondrule formation experiment, which was carried out at long-term microgravity aboard the International Space Station. In this experiment, freely levitating forsterite (Mg2SiO4) dust particles were exposed to electric arc discharges, thus simulating chondrule formation via nebular lightning. The arc discharges were able to melt single dust particles completely, which then crystallized with very high cooling rates of >105 K h−1. The crystals in the spherules show a crystallographic preferred orientation of the [010] axes perpendicular to the spherule surface, similar to the preferred orientation observed in some natural chondrules. This microstructure is probably the result of crystallization under microgravity conditions. Furthermore, the spherules interacted with the surrounding gas during crystallization. We show that this type of experiment is able to form spherules, which show some similarities with the morphology of chondrules despite very short heating pulses and high cooling rates.
The endemic argan tree (Argania spinosa) populations in southern Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth; however, it is unknown if the trees influence the soil of the intertree areas. Hypothetically, spatial differences in soil parameters of the intertree area should result from the translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. In total, 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) and the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) up to 50 m distance from the tree. They were analysed for gravimetric soil water content, pH, electrical conductivity, percolation stability, total nitrogen content (TN), content of soil organic carbon (SOC) and C/N ratio. A total of 74 tension disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with, e.g., SOC and TN content decreasing significantly from tree trunk (4.4 % SOC and 0.3 % TN) to tree drip line (2.0 % SOC and 0.2 % TN). However, intertree areas near the tree drip line (1.3 % SOC and 0.2 % TN) differed significantly from intertree areas between two trees (1.0 % SOC and 0.1 % TN) yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil water content was highest in the north due to shade from the midday sun; the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. This was the case on sites under different land usages (silvopastoral and agricultural), slope gradients or tree densities. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil water content or TN or SOC content to ensure seedling survival, along with measures to prevent overgrazing.
The endemic argan tree (Argania spinosa) populations in South Morocco are highly degraded due to overbrowsing, illegal firewood extraction and the expansion of intensive agriculture. Bare areas between the isolated trees increase due to limited regrowth, but show lower soil quality than their neighbouring tree areas. Hypothetically, spatial differences of soil quality of the intertree area should result from translocation of litter or soil particles (by runoff and erosion or wind drift) from canopy-covered areas to the intertree areas. 385 soil samples were taken around the tree from the trunk along the tree drip line (within and outside the tree area) as well as the intertree area between two trees in four directions (upslope, downslope and in both directions parallel to the slope) and analysed for soil moisture, pH, electrical conductivity, percolation stability, total nitrogen content, content of soil organic carbon and C/N ratio. 74 tension-disc infiltrometer experiments were performed near the tree drip line, within and outside the tree area, to measure the unsaturated hydraulic conductivity. We found that the tree influence on its surrounding intertree area is limited, with e.g., Corg- & N-content decreasing significantly from tree trunk to tree drip line. However, intertree areas near the tree drip line differed significantly from intertree areas between two trees, yet only with a small effect. Trends for spatial patterns could be found in eastern and downslope directions due to wind drift and slope wash. Soil moisture was highest in the north due to shade from the midday sun, the influence extended to the intertree areas. The unsaturated hydraulic conductivity also showed significant differences between areas within and outside the tree area near the tree drip line. Although only limited influence of the tree on its intertree area was found, the spatial pattern around the tree suggests that reforestation measures should be aimed around tree shelters in northern or eastern directions with higher soil moistures, N- or Corg-content to ensure seedling survival.
A general circulation model is used to study the interaction between parameterized gravity waves (GWs) and large-scale Kelvin waves in the tropical stratosphere. The simulation shows that Kelvin waves with substantial amplitudes (∼10 m s−1) can significantly affect the distribution of GW drag by modulating the local shear. Furthermore, this effect is localized to regions above strong convective organizations that generate large-amplitude GWs, so that at a given altitude it occurs selectively in a certain phase of Kelvin waves. Accordingly, this effect also contributes to the zonal-mean GW drag, which is large in the middle stratosphere during the phase transition of the quasi-biennial oscillation (QBO). Furthermore, we detect an enhancement of Kelvin-wave momentum flux due to GW drag modulated by Kelvin waves. The result implies an importance of GW dynamics coupled to Kelvin waves in the QBO progression.
Plain Language Summary: The variability of the tropical atmosphere at altitudes of about 18–40 km is dominated by a large-amplitude long-term oscillation of wind, the quasi-biennial oscillation, which has a broad impact on the climate and seasonal forecasting. This oscillation is known to be driven by various types of atmospheric waves with multiple spatial scales. Using a numerical model, this study reports a process of interaction between those waves on different scales, which has not been illuminated before. The result implies a potential importance of this process in the progression of the quasi-biennial oscillation. Proper model representations of these multiscale waves and tropical convection are required to simulate this process.
Previous investigation of seismic anisotropy indicates the presence of a simple mantle flow regime beneath the Turkish-Anatolian Plateau and Arabian Plate. Numerical modeling suggests that this simple flow is a component of a large-scale global mantle flow associated with the African superplume, which plays a key role in the geodynamic framework of the Arabia-Eurasia continental collision zone. However, the extent and impact of the flow pattern farther east beneath the Iranian Plateau and Zagros remains unclear. While the relatively smoothly varying lithospheric thickness beneath the Anatolian Plateau and Arabian Plate allows progress of the simple mantle flow, the variable lithospheric thickness across the Iranian Plateau is expected to impose additional boundary conditions on the mantle flow field. In this study, for the first time, we use an unprecedented data set of seismic waveforms from a network of 245 seismic stations to examine the mantle flow pattern and lithospheric deformation over the entire region of the Iranian Plateau and Zagros by investigation of seismic anisotropy. We also examine the correlation between the pattern of seismic anisotropy, plate motion using GPS velocities and surface strain fields. Our study reveals a complex pattern of seismic anisotropy that implies a similarly complex mantle flow field. The pattern of seismic anisotropy suggests that the regional simple mantle flow beneath the Arabian Platform and eastern Turkey deflects as a circular flow around the thick Zagros lithosphere. This circular flow merges into a toroidal component beneath the NW Zagros that is likely an indicator of a lateral discontinuity in the lithosphere. Our examination also suggests that the main lithospheric deformation in the Zagros occurs as an axial shortening across the belt, whereas in the eastern Alborz and Kopeh-Dagh a belt-parallel horizontal lithospheric deformation plays a major role.
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.
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.
Triple oxygen isotope measurements are an emerging tool in paleoclimate reconstructions. In this contribution we develop the application of triple oxygen isotope measurements to lacustrine sediments to reconstruct past elevations. We focus on a well-constrained sample set from the Eocene North American Cordillera (Cherty Limestone Formation, Elko Basin, NV, United States, 42–43.5 Ma) on the east side of the elevated Nevadaplano. We present triple oxygen isotope measurements on freshwater lacustrine chert samples from the Cherty Limestone Formation. Across an evaporation trend spanning 6.5‰ in δ18O values we observe a negative correlation with Δ′17O ranging from −0.066 to −0.111‰ (λRL = 0.528), with an empirical slope (λchert, δ′17O vs. δ′18O) of 0.5236. Additionally, we present new carbonate clumped isotope (Δ47) temperature results on the overlying fluvial-lacustrine Elko Formation, which indicate an error-weighted mean temperature of 32.5 ± 3.8°C (1σ), and evaporatively enriched lake water spanning δ18O values of −3.7 to +3.5‰ (VSMOW). Paired chert and carbonate δ18O values demonstrate that co-equilbrium among the carbonate and chert phases is unlikely. Thus, as also previously suggested, it is most likely that Elko Basin chert formed during early diagenesis in equilbirium with pore waters that reflect evaporatively 18O-enriched lake water. Using this scenario we apply a model for back-calculating unevaporated water composition to derive a source water of δ′18O = −16.1‰ (VSMOW), similar to modern local meteoric waters but lower than previous work on paired δ18O- δD measurements from the same chert samples. Further, this back-calculated unevaporated source water is higher than those derived using δD measurements of Late Eocene hydrated volcanic glass from the Elko Basin (average δ′18O equivalent of approximately −18.4‰, VSMOW). This suggests, assuming Eocene meteoric water Δ′17O values similar to today (∼0.032‰), either that: (1) the hypsometric mean elevation recorded by the lacustrine Cherty Limestone was lower than that derived from the average of the volcanic glass δD measurements alone; or (2) there was hydrogen exchange in volcanic glass with later low δD meteoric fluids. Nonetheless, our new findings support a relatively high (∼2.5–3 km) plateau recorded in the Elko Basin during the mid-Eocene.