550 Geowissenschaften
Refine
Year of publication
Document Type
- Article (672)
- Doctoral Thesis (116)
- Conference Proceeding (14)
- Working Paper (11)
- Book (6)
- Part of a Book (4)
- Master's Thesis (3)
- Preprint (2)
- Review (2)
- Bachelor Thesis (1)
Language
- English (832) (remove)
Has Fulltext
- yes (832)
Is part of the Bibliography
- no (832)
Keywords
- climate change (11)
- Climate change (7)
- COSMO-CLM (6)
- precipitation (6)
- Atmospheric chemistry (5)
- Palaeoclimate (5)
- Biogeochemistry (4)
- Geochemistry (4)
- Palaeoceanography (4)
- Bewässerung (3)
Institute
- Geowissenschaften (616)
- Geowissenschaften / Geographie (126)
- Biodiversität und Klima Forschungszentrum (BiK-F) (61)
- Senckenbergische Naturforschende Gesellschaft (45)
- Geographie (22)
- Biowissenschaften (21)
- Institut für Ökologie, Evolution und Diversität (6)
- Institut für sozial-ökologische Forschung (ISOE) (5)
- Frankfurt Institute for Advanced Studies (FIAS) (4)
- Extern (3)
The Altenberg–Teplice Volcanic Complex (ATVC) is a large ~ NNW–SSE trending volcano-plutonic system in the southern part of the Eastern Erzgebirge (northern Bohemian Massif, south-eastern Germany and northern Czech Republic). This study presents high precision U–Pb CA-ID-TIMS zircon ages for the pre-caldera volcano-sedimentary Schönfeld–Altenberg Complex and various rocks of the caldera stage: the Teplice rhyolite, the microgranite ring dyke, and the Sayda-Berggießhübel dyke swarm. These data revealed a prolonged time gap of ca. 7–8 Myr between the pre-caldera stage (Schönfeld–Altenberg Complex) and the climactic caldera stage. The volcanic rocks of the Schönfeld–Altenberg Complex represent the earliest volcanic activity in the Erzgebirge and central Europe at ca. 322 Ma. The subsequent Teplice rhyolite was formed during a relatively short time interval of only 1–2 Myr (314–313 Ma). During the same time interval (314–313 Ma), the microgranite ring dyke intruded at the rim of the caldera structure. In addition, one dyke of the Sayda-Berggiesshübel dyke swarm was dated at ca. 314 Ma, while another yielded a younger age (ca. 311 Ma). These data confirm the close genetic and temporal relationship of the Teplice rhyolite, the microgranite ring dyke, and (at least part of) the Sayda-Berggießhübel dyke swarm. Remarkably, the caldera formation in the south of the Eastern Erzgebirge (caldera stage of ATVC: 314–313 Ma) and that in the north (Tharandt Forest caldera: 314–312 Ma) occurred during the same time. These data document a large ~ 60 km NNW–SSE trending magmatic system in the whole Eastern Erzgebirge. For the first time, Hf-O-isotope zircon data was acquired on the ring dyke from the ATVC rocks to better characterize its possible sources. The homogeneous Hf-O-isotope zircon data from the microgranite ring dyke require preceding homogenization of basement rocks. Some small-scale melts that were produced during Variscan amphibolite-facies metamorphism show similar Hf-O-isotope characteristics and can therefore be considered as the most probable source for the microgranite ring dyke melt. In addition, a second source with low oxygen isotope ratios (e.g. basic rocks) probably contributed to the melt and possibly triggered the climactic eruption of the Teplice rhyolite as well as the crystal-rich intrusion of the ring dyke.
By means of available ice nucleating particle (INP) parameterization schemes we compute profiles of dust INP number concentration utilizing Polly-XT and CALIPSO lidar observations during the INUIT-BACCHUS-ACTRIS 2016 campaign. The polarization-lidar photometer networking (POLIPHON) method is used to separate dust and non-dust aerosol backscatter, extinction, mass concentration, particle number concentration (for particles with radius > 250 nm) and surface area concentration. The INP final products are compared with aerosol samples collected from unmanned aircraft systems (UAS) and analyzed using the ice nucleus counter FRIDGE.
Two types of particles exist in the atmosphere, primary and secondary particles. While primary particles such as soot, mineral dust, sea salt particles or pollen are introduced directly as particles into the atmosphere, secondary particles are formed in the atmosphere by condensation of gases. The formation of such new aerosol particles takes place frequently and at a broad variety of atmospheric conditions and geographic locations. A considerable fraction of the atmospheric particles is formed by such nucleation processes. The newly formed particles may grow by condensation to sizes where they are large enough to act as cloud condensation nuclei and therefore may affect cloud properties. The fundamental processes of aerosol nucleation are described and typical atmospheric observations are discussed. Two recent studies are introduced that potentially change our current understanding of atmospheric nucleation substantially.
The modern precipitation balance in southeastern (SE) Brazil is regulated by the South American summer Monsoon and threatened by global climate change. On glacial-interglacial timescales, monsoon intensity was strongly controlled by precession-forced changes in insolation. To date, relatively little is known about the spatiotemporal distribution of tropical precipitation in SE Brazil and the resulting variability of fluvial discharge on glacial-interglacial timescales. Here, we present X-ray diffraction-derived mineralogical data for the 150–70 ka period (marine isotope stage (MIS) 6 to MIS 5) from the Doce River basin. This area was sensitive to changes in monsoonal precipitation intensity due to its proximity to the South Atlantic Convergence Zone. The data, obtained from a marine sediment core (M125-55–7) close to the Doce river mouth (20°S), show pronounced changes in the Doce River suspension load’s mineralogical composition on glacial-interglacial and precessional timescales. While the ratio of silicates to carbonates displays precession-paced changes, the mineralogical composition of the carbonate-free fraction discriminates between two assemblages which strongly vary between glacial and interglacial time scales, with precession-forced variability only visible in MIS 5. The first assemblage, dominated by high contents of kaolinite and gibbsite, indicates intensified lowland erosion of mature tropical soils. The second one, characterized by higher contents of the well-ordered illite, quartz and albite, points to intensified erosion of immature soils in the upper Doce Basin. High kaolinite contents in the silicate fraction prevailed in late MIS 6 and indicate pronounced lowland soil erosion along a steepened topographic gradient. The illite-rich mineral assemblage was more abundant in MIS 5, particularly during times of high austral summer insolation, indicating strong monsoonal rainfall and intense physical erosion in the upper catchment. When the summer monsoon weakened in times of lower insolation, the mineral assemblage was dominated by kaolinite again, indicative of lower precipitation and runoff in the upper catchment and dominant lowland erosion.
Seasonal forecasting systems still have difficulties predicting temperature over continental regions, while their performance is better over some maritime regions. On the other hand, the land surface is a substantial source of (sub-)seasonal predictability. A crucial land surface component in focus here is the snow cover, which stores water and modulates the surface radiation balance. This paper’s goal is to attribute snow cover seasonal forecasting biases and lack of skill to either initialization or parameterization errors. For this purpose, we compare the snow representation in five seasonal forecasting systems (from DWD, ECMWF, Météo-France, CMCC, and ECCC) and their performances in predicting snow and 2-m temperature over a Siberian region against ERA5 reanalysis and station data. Although all systems use similar atmospheric and land initialization approaches and data, their snow and temperature biases differ in sign and amplitude. Too-large initial snow biases persist over the forecast period, delaying and prolonging the melting phase. The simplest snow scheme (used in DWD’s system) shows too-early and fast melting in spring. However, systems including multi-layer snow schemes (Météo-France and CMCC) do not necessarily perform better. Both initialization and parameterization are causes of snow biases, but, depending on the system, one can be more dominant.
We present the results of a multi-disciplinary investigation on a deciduous human tooth (Pradis 1), recently recovered from the Epigravettian layers of the Grotte di Pradis archaeological site (Northeastern Italian Prealps). Pradis 1 is an exfoliated deciduous molar (Rdm2), lost during life by an 11–12-year-old child. A direct radiocarbon date provided an age of 13,088–12,897 cal BP (95% probability, IntCal20). Amelogenin peptides extracted from tooth enamel and analysed through LC–MS/MS indicate that Pradis 1 likely belonged to a male. Time-resolved 87Sr/86Sr analyses by laser ablation mass spectrometry (LA-MC-ICPMS), combined with dental histology, were able to resolve his movements during the first year of life (i.e. the enamel mineralization interval). Specifically, the Sr isotope ratio of the tooth enamel differs from the local baseline value, suggesting that the child likely spent his first year of life far from Grotte di Pradis. Sr isotopes are also suggestive of a cyclical/seasonal mobility pattern exploited by the Epigravettian human group. The exploitation of Grotte di Pradis on a seasonal, i.e. summer, basis is also indicated by the faunal spectra. Indeed, the nearly 100% occurrence of marmot remains in the entire archaeozoological collection indicates the use of Pradis as a specialized marmot hunting or butchering site. This work represents the first direct assessment of sub-annual movements observed in an Epigravettian hunter-gatherer group from Northern Italy.
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.
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.
The calcareous substrate of spring-fed fens makes them unique islands of biodiversity, hosting endangered, vulnerable, and protected vascular plants. Hence, spring-fed fens ecosystems require special conservation attention because many of them are destroyed (e.g. drained, forested) and it is extremely difficult or even impossible to restore the unique hydrogeological and geochemical conditions enabling their function. The long-term perspective of paleoecological studies allows indication of former wetland ecosystem states and provides understanding of their development over millennia. To examine the late Holocene dynamics of a calcareous spring-fed fen (Raganu Mire) ecosystem on the Baltic Sea coast (Latvia) in relation to environmental changes, substrate and human activity, we have undertaken high-resolution analyses of plant macrofossils, pollen, mollusc, stable carbon (δ13C) and oxygen (δ18O) isotopes combined with radiocarbon dating (AMS) in three coring locations. Our study revealed that peat deposits began accumulating ca. 7000 cal. yr BP and calcareous deposits (tufa) from 1450 cal. yr BP, coinciding with regional hydrological changes. Several fire events occurred between 4000 and 1600 cal. yr BP, which appeared to have had a limited effect on local vegetation. The most significant changes in the forest and peatland ecosystems were at 3200 cal. yr BP associated with a dry climate stage and high fire activity, and then between 1400 and 500 cal. yr BP potentially associated with temperature changes during the Medieval Climate Anomaly (MCA) and Little Ice Age. Hydrological disturbances in the peatland catchment from 1400 cal. yr BP were most likely strengthened by human activity (deforestation) in this region. The relationship between the development of this peatland and changes in its catchment area, such as land cover changes or fluctuations in groundwater levels, suggest that protection and restoration of spring-fed fen ecosystems should also include the surrounding catchment. The presence of calcareous sediments, as well as appropriate temperature and local hydrological conditions appear to be the most crucial factors controlling Cladium marisus populations in our site - currently at the eastern limit of its distribution in Europe.
Non-forest ecosystems, dominated by shrubs, grasses and herbaceous plants, provide ecosystem services including carbon sequestration and forage for grazing, and are highly sensitive to climatic changes. Yet these ecosystems are poorly represented in remotely sensed biomass products and are undersampled by in situ monitoring. Current global change threats emphasize the need for new tools to capture biomass change in non-forest ecosystems at appropriate scales. Here we developed and deployed a new protocol for photogrammetric height using unoccupied aerial vehicle (UAV) images to test its capability for delivering standardized measurements of biomass across a globally distributed field experiment. We assessed whether canopy height inferred from UAV photogrammetry allows the prediction of aboveground biomass (AGB) across low-stature plant species by conducting 38 photogrammetric surveys over 741 harvested plots to sample 50 species. We found mean canopy height was strongly predictive of AGB across species, with a median adjusted R2 of 0.87 (ranging from 0.46 to 0.99) and median prediction error from leave-one-out cross-validation of 3.9%. Biomass per-unit-of-height was similar within but different among, plant functional types. We found that photogrammetric reconstructions of canopy height were sensitive to wind speed but not sun elevation during surveys. We demonstrated that our photogrammetric approach produced generalizable measurements across growth forms and environmental settings and yielded accuracies as good as those obtained from in situ approaches. We demonstrate that using a standardized approach for UAV photogrammetry can deliver accurate AGB estimates across a wide range of dynamic and heterogeneous ecosystems. Many academic and land management institutions have the technical capacity to deploy these approaches over extents of 1–10 ha−1. Photogrammetric approaches could provide much-needed information required to calibrate and validate the vegetation models and satellite-derived biomass products that are essential to understand vulnerable and understudied non-forested ecosystems around the globe.
Following votes in the Coniacian Working Group, the Cretaceous Subcommission and the International Commission on Stratigraphy, on May 1st, 2021, the International Union of Geological Sciences voted unanimously to ratify the Global Stratotype Section and Point (GSSP) proposal for the base of the Coniacian Stage of the Upper Cretaceous Series and Cretaceous System. The lower boundary of the Coniacian Stage is placed at the base of Bed 46 of the Salzgitter-Salder section in northern Germany. The boundary is defined by the first appearance of the inoceramid bivalve species Cremnoceramus deformis erectus (Meek) and complemented by the Navigation carbon isotope event. Additional data include the bivalve genus Didymotis, foraminifera, ammonite, nannofossil and organic-walled dinoflagellate cyst events. Three auxiliary sections (Słupia Nadbrzeżna, central Poland; Střeleč, Czech Republic; El Rosario, NE Mexico) supplement the details of the boundary record in various facies, and in differing geographic and biogeographic contexts.
The climate system is one of the classical examples of a complex dynamical system consisting of interacting sub-systems through mass, momentum, and energy exchange across various spatial and temporal scales. This thesis aims to detect and quantify sub-component interactions from an information exchange (IE) perspective. For this purpose, IE estimators derived from information theory are explored and applied to the available climate data obtained from observations, reanalysis, global and regional climate models. Specifically, this thesis investigates the usefulness of information theory methods for process-oriented climate model evaluation.
Firstly, methods derived from the concepts of information theory such as transfer entropy and information flow along with their linear and non-linear estimation techniques are initially tested and applied to idealized two-dimensional dynamical systems. The results revealed an expected direction and magnitude of IE providing insights into underlying dynamics. However, as expected the linear estimators are robust for linear systems but fail for non-linear systems. Though the non-linear estimators (kernel and kraskov) showed expected results for all the idealized systems, their free tuning parameters are to be tested for consistent results. Moreover, these methods are sensitive to the available time series length.
A real world example case study involving the dynamics between the Indian and Pacific oceans revealed a physically consistent bi-directional IE. However, unexpected IE was detected in the example of North Atlantic and European air temperatures indicating hidden drivers. Though IE provides insights into system dynamics, the availability of time series length and the system at hand must be carefully taken into account before inferring any possible interpretations of the results.
Quantifying the IE from El-Ni\~{n}o southern oscillation (ENSO) and Indian Ocean Dipole (IOD) to the Indian Summer Monsoon Rainfall (ISMR) with the observational and reanalysis data sets revealed that both ENSO and IOD are synergistic predictors for the inter-annual variability of the ISMR over central India i.e., the monsoon core region. Though the investigated three Global Climate Models (GCM) could not reveal the underlying IE dynamics of ENSO, IOD, and ISMR, a Regional Climate Model (RCM) simulation downscaling one of the GCMs with realistic large scale signals across the lateral boundaries showed good agreement with the observations.
Evaluating a coupled regional climate modeling system driven by two different global data sets with IE estimators revealed significant differences between the process chains linking the north-west Mediterranean sea surface temperatures, evaporation, wind speed, and the Vb-cyclone induced precipitation over Danube, Odra, and Elbe catchments in the historical period (1951-2005). Detailed investigation revealed that the north-west Mediterranean Sea in the coupled regional simulation driven by ERA-20C reanalysis corresponded to the Vb-cyclone precipitation over the three catchments while no such correspondence is noted in the EC-EARTH driven simulation. This discrepancy is attributed to the inheritance of the simulation biases from GCM into the RCM. In the future period (1965-2099), no significant changes in the processes are noted from the simulation.
Overall, this thesis used IE estimators in investigating the underlying dynamics of climate system and climate models. The estimators proved useful in providing insights into climate system dynamics assisting in a process based climate model evaluation.
Carbon is an element that controls planetary habitability, and is fundamental for life on Earth. Its behaviour has important consequences for the global climate system, the origin and evolution of life on Earth. While the biosphere and atmosphere’s carbon cycle only accounts for less than 1% of the global carbon budget, hidden reservoirs of deep carbon in the Earth’s interior comprise the predominant storage of carbon on the planet. At the Earth’s surface, 60-70 % of carbon is hosted by carbonate minerals, which are then transported to the Earth’s interior, mainly in the form of sediments, by subduction of the oceanic lithosphere. Subducting plates are subjected to decarbonation, dehydration, and melting with CO2 release via supra-subduction volcanism. Nevertheless, part of the subducted carbonates’ may survive and be further transported to the deep mantle. Direct evidence of the existence of carbonates in the Earth’s interior, possibly reaching down to the lower mantle, comes from the finding of syngenetic inclusions of carbonates in diamonds and mantle xenoliths. The presence of carbonates in the deep Earth has a critical effect on the physical properties of the mantle. Melting and chemical speciation of the mantle are strongly affected by the form of C and carbonate stability. Therefore, the study of the stability and physical properties of carbonates at high pressures and temperatures is fundamental, because understanding the processes involved in the deep carbon cycle helps to improve our picture of the whole mantle.
The systematic characterization of the elastic properties of carbonates as a function of their structure and chemical composition is of great importance because it may allow to identify their presence and distribution by seismology. Inverting seismic observations to successfully constrain the chemical composition and mineralogy of the Earth’s interior requires knowledge of the physical properties of all possible Earth’s materials at pressures and temperatures applicable to the Earth’s interior. Up to now, a multitude of studies has focused on the construction of phase diagrams and structural transitions by means of X-ray diffraction and vibrational spectroscopy experiments.
Few studies are available on the complete elastic tensor of carbonates, however most of the datasets are not accompanied by an accurate characterization of the samples, which are often solid solutions and the exact chemical composition, density or the details about the experimental methods used are not presented. The aim of this thesis is to study the effect of chemical composition on the elastic properties of carbonates, providing a reliable dataset on the elasticity of the main carbonates. In particular, the elastic properties of crystalline aragonite, CaCO3, and Fe-dolomite, (Ca, Mg, Fe)(CO3)2, with different compositions were studied by Brillouin spectroscopy at ambient conditions. Brillouin spectroscopy was also used to investigate the elastic behaviour of amorphous calcium carbonate samples with different water contents (up to 18 wt%) at high pressures, up to 20 GPa.
Furthermore, the importance of cationic substitution on the structure and high pressure behaviour of carbonates was investigated by studying a synthetic CaCO3-SrCO3 solid solution at ambient conditions and at high pressures, up to 10 GPa, by single crystal X-ray diffraction. Finally, the study of the effect of composition on the elastic properties of families of isostructural solids was also extended to a different class of materials, the metal guanidinium formates. The elasticity of a family of perovskite metal organic frameworks, metal guanidinium formates C(NH2)3MII(HCOO)3, with MII =Mn, Zn, Cu, Co, Cd and Ca was investigated by combining Brillouin spectroscopy, resonant ultrasound spectroscopy, density functional theory and thermal diffuse scattering analysis.
Extreme convective precipitation events are among the most severe hazards in central Europe and are expected to intensify under global warming. However, the degree of intensification and the underlying processes are still uncertain. In this thesis, recent advances in continuous, radar-based precipitation monitoring and convection-permitting climate modeling are used to investigate Lagrangian properties of convective rain cells such as precipitation intensity, cell area, and precipitation sum and their relationship to large-scale, environmental conditions.
Firstly, convective precipitation objects are tracked in a gauge-adjusted radar-data set and the properties of these cells are related to large-scale environmental variables to investigate the observed super-Clausius-Clapeyron (CC) scaling of convective extreme precipitation. The Lagrangian precipitation sum of convective cells increases with dew point temperature at rates well above the CC-rate with increasing rates for higher dew point temperatures. These varying, high rates are caused by a covarying increase of CAPE with dew point temperature as well as the effect of high vertical wind shear causing an increase in cell area and thus precipitation sum. At the same time, cells move faster at high vertical wind shear so that Eulerian scaling rates are lower than Lagrangian but still above the CC-rate. The results show that wind shear and static instability need to be taken into account when transferring precipitation scaling under current climate conditions to future conditions. Secondly, the representation of convective cell properties in the convection-permitting climate model COSMO-CLM is evaluated. The model can simulate the observed frequency distributions of cell properties such as lifetime, area, mean and maximum intensity, and precipitation sum. The increase of area and intensity with lifetime is also well captured despite an underestimation of the intensity of the most severe cells. Furthermore, the model can represent the temperature scaling of intensity, area, and precipitation sum but fails to simulate the observed increase of lifetime. Thus, the model is suitable to study climatologies of convective storms in Germany. Thirdly, two COSMO-CLM projections at the end of the century under emission scenario RCP8.5 were investigated. While the number of convective cells and their lifetime remain approximately constant compared to present conditions, intensity and area increase strongly. The relative increase of intensity and area is largest for the highest percentiles meaning that extreme events intensify the most. The characteristic afternoon maximum of convective precipitation is damped, and shifted to later times of day which leads to an increase of nighttime precipitation in the future. Scaling rates of cell properties with dew point temperature are nearly identical in present and future in the simulation driven by the EC-Earth model which means that the upper limit of cell properties like intensity, area, and precipitation sum could be predicted from near-surface dew point temperature. However, this result could not be reproduced by the simulation driven by MIROC5 and needs further investigation.
In this survey paper, we present a multiscale post-processing method in exploration. Based on a physically relevant mollifier technique involving the elasto-oscillatory Cauchy–Navier equation, we mathematically describe the extractable information within 3D geological models obtained by migration as is commonly used for geophysical exploration purposes. More explicitly, the developed multiscale approach extracts and visualizes structural features inherently available in signature bands of certain geological formations such as aquifers, salt domes etc. by specifying suitable wavelet bands.
Geochemical investigations on biogenic carbonates are commonly conducted to reconstruct the environmental conditions of the past. However, different carbonate producers incorporate elements to varying degrees, due to biological vital effects. Detecting and quantifying these effects is crucial to produce reliable reconstructions. These paleoreconstructions are of great importance to evaluate the consequences of our recent climate change and identify control mechanisms on the distribution of endangered species such as Desmophyllum pertusum. In chapter three we tested Mg/Ca, Sr/Ca and Na/Ca ratios on this species, among other coldwater scleractinians, to test if they provide reliable proxy information. The results reveal no apparent control of Mg/Ca or Sr/Ca ratios through seawater temperature, salinity or pH. Na/Ca ratios appear to be partly controlled by the seawater temperature, which is also true for other aragonitic organisms such as warm-water corals and the bivalve Mytilus edulis. However, a large variability complicates possible reconstructions by means of Na/Ca. In addition, we explore different models to explain the apparent temperature effect on Na/Ca ratios based on temperature sensitive Na and Ca pumping enzymes.
The bivalve Acesta excavata is commonly found in cold-water coral reefs among the North Atlantic, together with D. pertusum. Multiple linear regression analysis, presented in chapter four, indicates that up to 79% of the elemental variability in Mg/Ca, Sr/Ca and Na/Ca is explainable with temperature and salinity as independent predictor variables. Vital effects, for instance growth rate effects, are evident and make paleoreconstructions not feasible. Furthermore, organic material embedded in the shell, as well as possible stress effects can drastically change the elemental composition. Removal of these organic matrices from bulk samples for LA-ICP-MS (laser ablation inductively coupled mass spectrometer) measurements by means of oxidative cleaning is not possible, but Na/Ca ratios decrease after this cleaning. This is presumably an effect of leaching and not caused by the removal of organic matrices.
Interesting biogeochemical relations were found in the parasitic foraminifera H. sarcophaga. We report Mg/Ca, Sr/Ca, Na/Ca and Mn/Ca ratios measured in H. sarcophaga from two different host species (A. excavata and D. pertusum) in chapter five. Sr/Ca ratios are significantly higher in foraminifera that lived on D. pertusum. This could indicate that dissolved host material is utilized in shell calcification of H. sarcophaga, given the naturally higher strontium concentration in the aragonite of D. pertusum. Mn/Ca ratios are highest in foraminifera that lived on A. excavata but did not fully penetrate the host’s shell. Most likely, this represents a juvenile stadium of the foraminifera during which it feeds on the organic
periostracum of the bivalve, which is enriched in Mn and Fe. The isotopic compositions are similarly affected, both δ18O and δ13C values are significantly lower in foraminifera that lived 23on D. pertusum compared to specimen that lived on A. excavata. Again, this might represent the uptake of dissolved host material or different pH regimes in the calcifying fluid of the hosts (bivalve < 8, coral > 8) that control the extent of hydration/hydroxylation reactions. Temperature reconstructions are possible using stable oxygen isotopes on this foraminifera species; however, the results are only reliable if the foraminifera lived on A. excavata. Samples of H. sarcophaga from D. pertusum would lead to overestimations of the seawater temperature due to the lower δ18O values.
Apart from biological vital effects, storage and preservation methods can significantly change the geochemical composition of different marine biogenic carbonates. In chapter six this is presented on the example of ethanol preservation, a common technique to allow extended storage of biogenic samples. The investigation reveals a significant decrease of Mg/Ca and Na/Ca ratios even after only 45 days storage in ultrapure ethanol. Sr/Ca ratios on the other hand are not influenced.
Besides temperature, salinity and pH further environmental parameters are important such as nutrient availability, especially for the distribution of cold-water corals. In chapter seven we extend the investigations on A. excavata by including the elemental ratios Ba/Ca, Mn/Ca and P/Ca. We expected P/Ca to be helpful in the otherwise difficult process of dentifying growth increments. Based on our observations we had to refute this theory. P/Ca ratios are not systematically enriched in the vicinity of growth lines. Instead, we found a regular sequence of peaks of Ba/Ca, P/Ca and Mn/Ca. This sequence as well as the peaks in general are potentially caused by equential blooms of different algae, diatoms and other planktonic organisms ...
As part of two drilling campaigns of the International Continental Scientific Drilling Program (ICDP), several geophysical borehole measurements were carried out by the Leibniz Institute for Applied Geophysics (LIAG) in two lakes. The acquired data was used to answer stratigraphic and paleoclimatic research questions, including the establishment of robust age-depth models and the construction of continuous lithological profiles.
Lake Towuti is located on Sulawesi (Indonesia), within the "Indo-Pacific Warm Pool" (IPWP), a globally important region for atmospheric heat and moisture budgets. The lake exists for approximately one million years, but its exact age is uncertain. We present the first agedepth model for the approximately 100 m continuous sediment sequence from the central part of the lake. The basis for this model is the magnetic susceptibility measured in the borehole and a tephra layer with an age of about 797 ka at 72 m depth. Our age-depth model is inferred from cyclostratigraphic analysis of borehole data and covers a period from 903 ± 11 to 131 ± 67 ka. We suggest that orbital eccentricity and/or changes between global cold and warm periods are responsible for hydroclimatic changes in the IPWP, that these changes affect sedimentation processes in Lake Towuti, and that we can measure and observe this effect in the sediment properties today. Additionally, we created a continuous artificial lithological profile from a series of different borehole data using cluster analysis. This provides information from parts of the borehole where no sediment is available due to core loss.
Lake Ohrid is 1.36 million years old and is located on the Balkan Peninsula on the border between Albania and North Macedonia. The primary hole 'DEEP' in the central part of the lake has been the subject of several investigations, but information about sediments of the marginal locations 'Pestani' and 'Cerava' have not been published yet. In our study, we use natural gamma radiation (GR) measured in the borehole to generate an age-depth model for DEEP. This is performed using the correlation of GR to the global LR04 reference record of Lisiecki and Raymo (2005).
The age information is then transferred via prominent seismic marker horizons to the other two sites, Pestani and Cerava, where it provides the first age-control points for the construction of age-depth models from correlation of GR to LR04. The generated age-depth models are tested using cyclostratigraphic methods, but the limits of this approach are revealed. At DEEP, sedimentation rates (SR) from the cyclostratigraphic method and the correlative approach differ by 2.8 %, at Pestani this difference is 16.7 %, and at Cerava the quality of the data does not allow a reliable evaluation of SR using the cyclostratigraphic approach. We used cluster analysis to construct artificial lithological profiles at all three sites and integrated them into the respective age-depth models. This enables us to determine which sediment types were deposited at what time, and we recognize the change between warm and cold periods in the sediment properties at all three locations. The analyses in this study were all performed on borehole and seismic data and thus do not involve sediment core data. Especially at Pestani and Cerava, new insights into the sedimentological history of Lake Ohrid could be obtained.
In the last part we discuss the occurrence of the half-precession (HP) signal in the European region during the last one million years. The focus is on Lake Ohrid, but a range of other proxies, from the eastern Mediterranean, across the European continent, up to Greenland are analyzed in regards to HP. Applying filters, we focus on the frequency range with a period of 13-8.5 ka and only HP remains in the records. We use correlative methods to determine the clarity of the HP signal in proxies distributed across the European realm. Additionally, we determined the development of HP over time. The HP signal is clearest in the southeast and decreases toward the north. It is further more pronounced in interglacial periods and in the younger part (<621 ka) of most proxies. We suggest that there are mechanisms that transmit the HP signal from its origin near the equator to higher latitudes via different processes. In this context, for instance, the African monsoon, the Nile River and the Mediterranean outflow via the Strait of Gibraltar can be important factors.
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.
Metal artifacts from the Paleometal Epoch (ca. 1100 BC–400 AD) of the Primorye (Russian Far East) have shed new light on the introduction of the earliest bronzes into the Pacific coastal areas of prehistoric Eurasia. However, little is known about raw material circulation and the role of metal in the context of inter-regional exchange. This paper investigates 12 copper artifacts from major Paleometal settlements using alloy composition, trace elements, and lead isotopes to explore the metal sources and distribution networks. The results suggest that most objects are made of a copper-tin alloy, but some have arsenic as a significant minor element . Geologically, copper is unlikely to have come from local ore sources, but rather from the Liaoxi corridor and Liaodong Peninsula in Northeast China. This may indicate an inland route of metal trade across Northeast China or alternately, a coastal route via the northern Korean Peninsula. Archaeologically, the combined study of artifact typology and chemistry indicates two possible origins for the metal: the Upper Xiajiadian culture in Northeast China and Slab Grave culture in Mongolia/Transbaikal. Remarkably, the connection with Upper Xiajiadian communities parallels the transport route along which millet agriculture spread from Northeast China to the Primorye during the Neolithic.
Community trait assembly in highly diverse tropical rainforests is still poorly understood. Based on more than a decade of field measurements in a biodiversity hotspot of southern Ecuador, we implemented plant trait variation and improved soil organic matter dynamics in a widely used dynamic vegetation model (the Lund-Potsdam-Jena General Ecosystem Simulator, LPJ-GUESS) to explore the main drivers of community assembly along an elevational gradient. In the model used here (LPJ-GUESS-NTD, where NTD stands for nutrient-trait dynamics), each plant individual can possess different trait combinations, and the community trait composition emerges via ecological sorting. Further model developments include plant growth limitation by phosphorous (P) and mycorrhizal nutrient uptake. The new model version reproduced the main observed community trait shift and related vegetation processes along the elevational gradient, but only if nutrient limitations to plant growth were activated. In turn, when traits were fixed, low productivity communities emerged due to reduced nutrient-use efficiency. Mycorrhizal nutrient uptake, when deactivated, reduced net primary production (NPP) by 61–72% along the gradient. Our results strongly suggest that the elevational temperature gradient drives community assembly and ecosystem functioning indirectly through its effect on soil nutrient dynamics and vegetation traits. This illustrates the importance of considering these processes to yield realistic model predictions.