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Precipitation extremes with devastating socioeconomic consequences within the South American Monsoon System (SAMS) are expected to become more frequent in the near future. The complexity in SAMS behavior, however, poses severe challenges for reliable future projections. Thus, robust paleomonsoon records are needed to constrain the high spatiotemporal variability in the response of SAMS rainfall to different climatic drivers. This study uses Ti/Ca ratios from X‐ray fluorescence scanning of a sediment core retrieved off eastern Brazilian to trace precipitation changes over the past 322 Kyr. The results indicate that despite the spatiotemporal complexity of the SAMS, insolation forcing is the primary pacemaker of variations in the monsoonal system. Additional modulation by atmospheric pCO2 suggests that SAMS intensity over eastern Brazil will be suppressed by rising CO2 emissions in the future. Lastly, our record reveals an unprecedented strong and persistent wet period during Marine Isotope Stage 6 driven by anomalously strong trade winds.
The complex magnetotelluric (MT) apparent resistivity tensor can be decomposed into two real tensors, the apparent resistivity and the resistivity phase tensors, which represent relationships between the observed electric field at a point on the Earth's surface and an associated apparent current density. We explain the differences between these tensors and conventional estimates of apparent resistivity and phase for simple resistivity environments and demonstrate, using canonical models in 1‐D and 2‐D environments, that both tensors are more sensitive to vertical and horizontal resistivity gradients than their conventional counterparts. The properties of the new tensors are explained using electromagnetic induction theory and the effects of associated charges at resistivity boundaries. We introduce a new way to plot tensor ellipses, which brings significant improvements to the interpretation of MT data, using appropriate visualization software. The apparent resistivity tensor gives information about the magnitude and direction of apparent resistivity subsurface structures and has a strong response to vertical resistivity contrasts. The resistivity phase tensor is highly sensitive to vertical boundaries and the associated fields in the TM mode. It is also free from static distortions under the same conditions implied for the conventional phase tensor. These findings have prompted a study in the potential of the new tensors for 3‐D inversions. The results from a 3‐D inversion of a canonical oblique conductor straddling two quarter spaces show distinct improvements in resolving the boundaries of the conductor and open a promising field for future studies.
The endemic argan woodlands cover large parts of South Morocco and create a characteristic landscape with areas of sparsely vegetated and bare soil surfaces between single trees. This unique ecosystem has been under extensive agrosilvopastoral management for centuries and is now at risk of degradation caused by overgrazing and increasing scarcity and variability of rainfall.
To investigate susceptibility to wind erosion, we conducted an experimental–empirical study including wind tunnel tests and a drone‐generated digital elevation model and quantified wind‐erodible material on five different associated surface types by means of sediment catchers. The highest emission flux was measured on freshly ploughed surfaces (1875 g m–2 h–1), while older ploughed areas with a re‐established crust produced a much lower emission flux (795 g m–2 h–1). Extensive tillage may have been a sustainable practice for generations, but increasing drought and uncertainty of rainfall now lead to an acute risk of severe soil erosion and dust production. The typical crusted surfaces characterized by residual rock fragment accumulation and wash processes produced the second highest emission flux (1,354 g m–2 h–1). Material collected from tree‐shaded areas (933 g m–2 h–1) was revealed to be a considerable source of organic material, possibly affecting substrate conditions positively on a larger regional scale. The lowest flux was measured on rock fragment‐covered surfaces (301 g m–2 h–1).
The data show that open argan woodland may be a considerable source for wind erosion and dust production, depending on surface characteristics strongly related to management. An adapted management must include the conservation of argan trees to offer a promising approach to prevent severe wind erosion and dust production and mitigate possible impacts of land‐use change and climate change related shifts in wind and rainfall patterns.
A realistic simulation of the atmospheric boundary layer (ABL) depends on an accurate representation of the land–atmosphere coupling. Land surface temperature (LST) plays an important role in this context and the assimilation of LST can lead to improved estimates of the boundary layer and its processes. We assimilated synthetic satellite LST retrievals derived from a nature run as truth into a fully coupled, state‐of‐the‐art land–atmosphere numeric weather prediction model. As assimilation system a local ensemble transform Kalman filter was used and the control vector was augmented by the soil temperature and humidity. To evaluate the concept of the augmented control vector, two‐day case‐studies with different control vector settings were conducted for clear‐sky periods in March and August 2017. These experiments with hourly LST assimilation were validated against the nature run and overall, the RMSE of atmospheric and soil temperature of the first‐guess (and analysis) were reduced. The temperature estimate of the ABL was particularly improved during daytime as was the estimate of the soil temperature during the whole diurnal cycle. The best impact of LST assimilation on the soil and the ABL was achieved with the augmented control vector. Through the coupling between the soil and the atmosphere, the assimilation of LST can have a positive impact on the temperature forecast of the ABL even after 15 hr because of the memory of the soil. These encouraging results motivate further work towards the assimilation of real satellite LST retrievals.
The continental expression of global cooling during the Miocene Climate Transition in Central Asia is poorly documented, as the tectonically active setting complicates the correlation of Neogene regional and global climatic developments. This study presents new geochemical data (CaSO4 content, carbonate δ13C and δ18O) from the endorheic alluvial‐lacustrine Aktau succession (Ili Basin, south‐east Kazakhstan) combined with findings from the previously published facies evolution. Time series analysis revealed long‐eccentricity forcing of the paleohydrology throughout the entire succession, split into several facies‐dependent segments. Orbital tuning, constrained by new laser ablation U‐Pb dates and a preexisting magnetostratigraphy, places the succession in a 5.0 Ma long interval in the middle to late Miocene (15.6 to 10.6 Ma). The long‐term water accumulation in the Ili Basin followed the timing of the Miocene Climate Transition, suggesting increased precipitation in the catchment area in response to climate cooling and stronger westerly winds. This was paced by minima of the 2.4 Ma eccentricity cycle, which favored the establishment of a discharge playa (~14.3 Ma) and a perennial lake (12.6 to 11.8 Ma). Furthermore, low obliquity amplitudes (nodes) caused a transient weakening of the westerlies at ~13.7 to 13.5 Ma and at ~12.7 Ma, resulting in negative hydrological budgets and salinization. Flooding of the windward Ili Basin coeval with aridification in the leeward basins suggests that the Tian Shan was a climate boundary already in the middle Miocene. Our results emphasize the impact of climate fluctuations on the westerlies' strength and thus on Central Asian hydrology.
An easy-to-use model to evaluate conductivities at high and middle latitudes in the height range 70–100 km is presented. It is based on electron density profiles obtained with the EISCAT VHF radar during 11 years and on the neutral atmospheric model MSIS95. The model uses solar zenith angle, geomagnetic activity and season as input parameters. It was mainly constructed to study the properties of Schumann resonances that depend on such conductivity profiles.
Remote sensing data are essential for monitoring the Earth’s surface waters, especially since the amount of publicly available in-situ data is declining. Satellite altimetry provides valuable information on the water levels and variations of lakes, reservoirs and rivers. In combination with satellite imagery, the derived time series allow the monitoring of lake storage changes and river discharge. However, satellite altimetry is limited in terms of its spatial resolution due to its measurement geometry, only providing information in the nadir direction beneath the satellite’s orbit. In a case study in the Mississippi River Basin (MRB), this study investigates the potential and limitations of past and current satellite missions for the monitoring of basin-wide storage changes. For that purpose, an automated target detection is developed and the extracted lake surfaces are merged with the satellites’ tracks. This reveals that the current altimeter configuration misses about 80% of all lakes larger than 0.1 km2 in the MRB and 20% of lakes larger than 10 km2, corresponding to 30% and 7% of the total water area, respectively. Past altimetry configurations perform even more poorly. From the larger water bodies represented by a global hydrology model, at least 91% of targets and 98% of storage changes are captured by the current altimeter configuration. This will improve significantly with the launch of the planned Surface Water and Ocean Topography (SWOT) mission.
Increases in water demand often result in unsustainable water use, leaving insufficient amounts of water for the environment. Therefore, water-saving strategies have been introduced to the environmental policy agenda in many (semi)-arid regions. As many such interventions failed to reach their objectives, a comprehensive tool is needed to assess them. We introduced a constructive framework to assess the proposed strategies by estimating five key components of the water balance in an area: (1) Demand; (2) Availability; (3) Withdrawal; (4) Depletion and (5) Outflow. The framework was applied to assess the Urmia Lake Restoration Program (ULRP) which aimed to increase the basin outflow to the lake to reach 3.1 × 109 m3 yr−1. Results suggested that ULRP could help to increase the Outflow by up to 57%. However, successful implementation of the ULRP was foreseen to be impeded because of three main reasons: (i) decreasing return flows; (ii) increased Depletion; (iii) the impact of climate change. Decreasing return flows and increasing Depletion were expected due to the introduction of technologies that increase irrigation efficiency, while climate change could decrease future water availability by an estimated 3–15%. We suggest that to reach the intervention target, strategies need to focus on reducing water depletion rather than water withdrawals. The framework can be used to comprehensively assess water-saving strategies, particularly in water-stressed basins.
Ice nucleating particle concentrations of the past: insights from a
600 year old Greenland ice core
(2020)
Ice nucleating particles (INPs) affect the microphysics in cloud and precipitation processes. Hence, they modulate the radiative properties of clouds. However, atmospheric INP concentrations of the past are basically unknown. Here, we present INP measurements from an ice core in Greenland, which dates back to the year 1370. In total 135 samples were analyzed with the FRIDGE droplet freezing assay in the temperature range from −14 ◦C to −35 ◦C. The sampling frequency was set to 1 in 10 years from 1370 to 1960. From 1960 to 1990 the frequency was increased to 1 sample per year. Additionally, a number of special events were probed, including volcanic episodes. The typical time coverage of a sample was on the order of a few months. Historical atmospheric INP concentrations were estimated with a conversion factor, which depends on the snow accumulation rate of the ice core, particle dry deposition velocity and the wet scavenging ratio. Typical atmospheric INP concentrations were on the order of 0.1 L -1 at −25 ◦C. The INP variability was found to be about 1 – 2 orders of magnitude. Yet, the short-term variability from samples over a seasonal cycle was considerably lower. INP concentrations were significantly correlated to chemical tracers derived from continuous flow analysis (CFA) and ion chromatography (IC) over a broad range of nucleation temperatures. The highest correlation coefficients were found for the particle concentration (dp > 1.2 µm). The correlation is higher for the seasonal samples, where INP concentrations follow a clear annual pattern, highlighting the importance of the annual dust input in Greenland from East Asian deserts during spring. Scanning electron microscopy (SEM) of single particles retrieved from selected samples found particles of soil origin to be the dominant fraction, verifying the significance of mineral dust particles as INPs. Overall, the concentrations compare reasonably well to present day INP concentrations, albeit they are on the lower side. However, we found that the INP concentration at medium supercooled temperatures differed before and after 1960. Average INP concentrations at −23 ◦C, −24 ◦C, −25 ◦C, −26 ◦C and −28 ◦C were significantly higher (and more variable) in the modern day period, which could indicate a potential anthropogenic impact or some post-coring contamination of the topmost, very porous firn.
Ice-nucleating particle concentrations of the past: insights from a 600-year-old Greenland ice core
(2020)
Ice-nucleating particles (INPs) affect the microphysics in cloud and precipitation processes. Hence, they modulate the radiative properties of clouds. However, atmospheric INP concentrations of the past are basically unknown. Here, we present INP measurements from an ice core in Greenland, which dates back to the year 1370. In total 135 samples were analyzed with the FRIDGE droplet freezing assay in the temperature range from −14 to −35 ∘C. The sampling frequency was set to 1 in 10 years from 1370 to 1960. From 1960 to 1990 the frequency was increased to one sample per year. Additionally, a few special events were probed, including volcanic episodes. The typical time coverage of a sample was on the order of a few months. Historical atmospheric INP concentrations were estimated with a conversion factor, which depends on the snow accumulation rate of the ice core, particle dry deposition velocity, and wet scavenging ratio. Typical atmospheric INP concentrations were on the order of 0.1 L−1 at −25 ∘C. The INP variability was found to be about 1–2 orders of magnitude. Yet, the short-term variability from samples over a seasonal cycle was considerably lower. INP concentrations were significantly correlated to some chemical tracers derived from continuous-flow analysis (CFA) and ion chromatography (IC) over a broad range of nucleation temperatures. The highest correlation coefficients were found for the particle concentration (spherical diameter dp > 1.2 µm). The correlation is higher for a time period of seasonal samples, where INP concentrations follow a clear annual pattern, highlighting the importance of the annual dust input in Greenland from East Asian deserts during spring. Scanning electron microscopy (SEM) analysis of selected samples found mineral dust to be the dominant particle fraction, verifying their significance as INPs. Overall, the concentrations compare reasonably well to present-day INP concentrations, albeit they are on the lower side. However, we found that the INP concentration at medium supercooled temperatures differed before and after 1960. Average INP concentrations at −23, −24, −25, −26, and −28 ∘C were significantly higher (and more variable) in the modern-day period, which could indicate a potential anthropogenic impact, e.g., from land-use change.
In this study, we use simulations from seven global vegetation models to provide the first multi‐model estimate of fire impacts on global tree cover and the carbon cycle under current climate and anthropogenic land use conditions, averaged for the years 2001–2012. Fire globally reduces the tree covered area and vegetation carbon storage by 10%. Regionally, the effects are much stronger, up to 20% for certain latitudinal bands, and 17% in savanna regions. Global fire effects on total carbon storage and carbon turnover times are lower with the effect on gross primary productivity (GPP) close to 0. We find the strongest impacts of fire in savanna regions. Climatic conditions in regions with the highest burned area differ from regions with highest absolute fire impact, which are characterized by higher precipitation. Our estimates of fire‐induced vegetation change are lower than previous studies. We attribute these differences to different definitions of vegetation change and effects of anthropogenic land use, which were not considered in previous studies and decreases the impact of fire on tree cover. Accounting for fires significantly improves the spatial patterns of simulated tree cover, which demonstrates the need to represent fire in dynamic vegetation models. Based upon comparisons between models and observations, process understanding and representation in models, we assess a higher confidence in the fire impact on tree cover and vegetation carbon compared to GPP, total carbon storage and turnover times. We have higher confidence in the spatial patterns compared to the global totals of the simulated fire impact. As we used an ensemble of state‐of‐the‐art fire models, including effects of land use and the ensemble median or mean compares better to observational datasets than any individual model, we consider the here presented results to be the current best estimate of global fire effects on ecosystems.
Aim: Plant life‐forms characterize key morphological strategies that enable large‐scale comparisons of plant communities. This study applies Raunkiær's plant life‐form concept that was developed for temperate climate to a subtropical island flora, in parts, dominated by summer aridity. We quantify how plant life‐form patterns as well as patterns of important plant functional traits (PFTs) relate to important climate and topographic characteristics.
Location: La Palma, Canary Islands.
Taxon: Flora of La Palma.
Methods: We assigned each native plant species a plant life‐form, that is, phanerophyte, chamaephyte, hemicryptophyte, geophyte and therophyte, as well as PFTs (succulence and N‐fixer). We used stacked species distribution models to assess occurrence probability for each species using the Atlantis database (500 m × 500 m grid). We related richness and percentage values for each plant life‐form and PFT to climate and topography.
Results: Plant life‐forms and PFTs showed a clear pattern within geographic but also climate space, while topography had a minor effect. Phanerophytes mainly contributed to the flora in humid areas. Chamaephytes and hemicryptophytes most strongly contributed to the summit scrub flora and, to some degree, also to the arid coastal regions. Geophytes and therophytes were mainly found in dry coastal regions. N‐fixers contributed mainly to warm‐arid and cool‐arid regions, while succulent species were mainly found in arid coastal regions.
Main conclusions: Raunkiær's plant life‐form concept can be comprehensively transferred to a subtropical island flora by adapting to local unfavourable growing conditions, that is, aridity. Using the strong environmental gradients offered by our study island, we identify substantial climate‐driven variation in patterns of plant life‐forms and PFTs that might be used for large‐scale comparisons in macroecological studies. The growth strategies reflected in Raunkiær's plant life‐forms suggest differences in species establishment and coexistence dynamics within different parts of the island's climate space.
We apply seismic full waveform inversion to SH‐ and Love‐wave data for investigating the near‐surface lithology at an archaeological site. We evaluate the resolution of the applied full waveform inversion algorithm through ground truthing in the form of an excavation and sediment core studies. Thereby, we investigate the benefits of full waveform inversion in comparison with other established methods of near‐surface prospecting in terms of resolution capabilities and interpretation security. The study is performed in a presumed harbour area of the ancient Thracian city of Ainos. The exemplary target is the source of a linear magnetic anomaly oriented perpendicular to the coast, which was found in a previous magnetic gradiometry survey, suggesting a mole. The SH‐wave full waveform inversion recovered a subsurface SH‐wave velocity model with submeter resolution showing lateral and vertical velocity variation between 40 and 150 m/s. To tame the non‐linearity of the full waveform inversion, a sequential inversion of frequency bands has to be combined with time‐windowing in order to separate the Love wave from the reflected SH wavefield. We compare the full waveform inversion results with multichannel analysis of surface waves, standard seismic reflection imaging, electrical resistivity tomography and electromagnetic induction. It turns out that the respective depth sections are correlated to a certain degree with the full waveform inversion results. However, the structural resolution of the other geophysical methods is significantly lower than for the full waveform inversion. An exception is the reflection seismic imaging, which shows the same resolution as full waveform inversion but can only be interpreted together with the full waveform inversion–based velocity model. An archaeological excavation as well as coring data allows ground truthing and a direct understanding of the geophysical structures. The results show that the target was a sort of near‐surface trench of about 3–4 m width and 0.8 m to 1.0 m depth, filled with silty sediment, which differs from the layered surrounding in colour and composition. The ground truthing revealed that only SH‐wave full waveform inversion and seismic reflection imaging could image the trench and sediment structure with satisfying lateral and depth resolution. We emphasize that the velocity distribution from SH‐wave full waveform inversion agrees closely with the excavated subsurface structures, and that the discovered changes in seismic velocity correlate with changes in the sand content in the respective sediment facies sequences. The study demonstrated that SH‐wave full waveform inversion is capable to image structural and lithological changes in the near subsurface at scales as low as 0.5 m, thus providing the high resolution needed for archaeological and geoarchaeological prospection.
Opportunities and challenges for paleoaltimetry in "small" orogens: insights from the European Alps
(2020)
Many stable isotope paleoaltimetry studies have focused on paleoelevation reconstructions of orogenic plateaus such as the Tibetan or Andean Plateaus. We address the opportunities and challenges of applying stable isotope paleoaltimetry to “smaller” orogens. We do this using a high‐resolution isotope tracking general circulation model (ECHAM5‐wiso) and explore the precipitation δ18O (δ18Op) signal of Cenozoic paleoclimate and topographic change in the European Alps. Results predict a maximum δ18Op change of 4–5‰ (relative to present day) during topographic development of the Alps. This signal of topographic change has the same magnitude as changes in δ18Op values resulting from Pliocene and Last Glacial Maximum global climatic change. Despite the similar magnitude of the isotopic signals resulting from topographic and paleoclimate changes, their spatial patterns across central Europe differ. Our results suggest that an integration of paleoclimate modeling, multiproxy approaches, and low‐elevation reference proxy records distal from an orogen improve topographic reconstructions.
Global‐scale gradient‐based groundwater models are a new endeavor for hydrologists who wish to improve global hydrological models (GHMs). In particular, the integration of such groundwater models into GHMs improves the simulation of water flows between surface water and groundwater and of capillary rise and thus evapotranspiration. Currently, these models are not able to simulate water table depth adequately over the entire globe. Unsatisfactory model performance compared to well observations suggests that a higher spatial resolution is required to better represent the high spatial variability of land surface and groundwater elevations. In this study, we use New Zealand as a testbed and analyze the impacts of spatial resolution on the results of global groundwater models. Steady‐state hydraulic heads simulated by two versions of the global groundwater model G3M, at spatial resolutions of 5 arc‐minutes (9 km) and 30 arc‐seconds (900 m), are compared with observations from the Canterbury region. The output of three other groundwater models with different spatial resolutions is analyzed as well. Considering the spatial distribution of residuals, general patterns of unsatisfactory model performance remain at the higher resolutions, suggesting that an increase in model resolution alone does not fix problems such as the systematic overestimation of hydraulic head. We conclude that (1) a new understanding of how low‐resolution global groundwater models can be evaluated is required, and (2) merely increasing the spatial resolution of global‐scale groundwater models will not improve the simulation of the global freshwater system.
Barriereinseln und Außensände, geformt durch eine Kombination aus Wind, Wellen, Strömung und Küstenlängstransport gelten als morphologisch hoch aktive Küstenbereiche und variieren häufig in Ursprung, Genese und Entwicklung. Sie besitzen durch ihre dissipative Wirkungsweise eine bedeutende Schutzfunktion für rückwärtige Inseln, Halligen und Festlandbereiche und bilden vor der Küste Nordfrieslands die westliche Außengrenze des Wattenmeeres.
Ziel der nachfolgenden Studie ist es, anhand hochauflösender Georadarmessungen und sedimentologischer Daten aus Bohrungen die Landschaftsgeschichte an der Westküste Amrums sowie die Entstehung und interne sedimentäre Architektur des der Insel westlich angelagerten Kniepsandes zu untersuchen und die Prozesse, die zur Genese geführt haben, durch Datierungen zeitlich einzuordnen. Auf Grundlage der gewonnenen Daten wurden zwei stratigraphische Modelle entwickelt, welche die geologisch-geomorphologischen Prozesse und Sedimentationsbedingungen im Westküstenvorfeld erklären.
Ein Modell zeigt die Landschaftsentwicklung an der Westküste Amrums und beschreibt die Sedimentationsbedingungen, die im Vorfeld der Westküste herrschten, bevor der Kniepsand an die Insel heranwanderte. Auf der Landoberfläche des ertrinkenden saaleeiszeitlichen Geestkerns wurden zu Beginn der Flandrischen Transgression feinkörnige Sedimente eines Mischund Schlickwatts abgelagert. Es ist davon auszugehen, dass der damals noch weit vor der Küste Amrums liegende Kniepsand eine Barriere bildete und so an der heute hochenergetischen Westküste für strömungsberuhigte Sedimentationsbedingungen sorgte. Durch Erosion am Geestkern bildeten sich in unterschiedlichen Höhenpositionen fossile Kliffs, die dem damaligen Meeresspiegelstand entsprechen.
Ein weiteres Modell beschreibt den Andockmechanismus des Kniepsandes an die Insel Amrum. Durch die Anlagerung des ehemaligen Außensandes und den damit einhergehenden Sedimentinput wurden die Bedingungen für eine großflächige Dünenbildung geschaffen.
Als erste Ergebnisse der derzeit laufenden paläomagnetischen Untersuchungen im Rhein-Main-Gebiet werden die Befunde von einigen stratigraphisch bedeutenden Profilen mitgeteilt. Während die Remanenzwerte aus altpleistozänen Tonen der Kelsterbacher Terrasse mit einer Ausnahme revers sind, konnte im Autobahneinschnitt Abenheim (NW Worms) und im Lößprofil der Ziegeleigrube Bad Soden am Taunus der Ubergang von reverser zu normaler Magnetisierung gefunden werden. Die Grenze zwischen MATUYAMA- und BRUNHES-Epoche liegt im Profil Bad Soden unter dem 6., das Jaramillo-Event unter dem 7. fossilen Bt-Horizont.
Die über dem letztinterglazialen Boden (Parabraunerde bzw. pseudovergleyte Parabraunerde) folgenden würmzeitlichen äolischen Sedimente können durch kennzeichnende Bodenhorizonte in 3 Abschnitte (Alt-, Mittel- und Jungwürm) gegliedert werden. Charakteristisch für das Altwürm sind Humuszonen, für das Mittelwürm neben einigen „Naßböden" braune Verlehmungszonen bis zu einer Mächtigkeit von 1,1 m und für das Jungwürm mehrere schwach ausgebildete, geringmächtige Verbraunungszonen und „Naßböden". Den wichtigsten Leithorizont des Jungwürms bildet das Kärlicher Tuffbändchen, das in jüngster Zeit auch in Nordhessen aufgefunden wurde. Abschließend wird das in Hessen aufgestellte Gliederungsschema mit den Würmlöß-Gliederungen in anderen Teilen Europas verglichen und eine Parallelisierung versucht.
Der Auffassung, das Substrat der Lockerbraunerde auf dem Oberwald des Vogelsberges sei ausschließlich ein äolisches Sediment der Jüngeren Tundrenzeit, wird widersprochen. Verschiedene Befunde, vor allem 14C-Datierungen, lassen vielmehr den Schluß zu, daß große Teile des Substrates vieler Lockerbraunerden holozäne anthropogene Kolluvien sind. Bekräftigt wird dagegen der Befund gleichen (jungtundrenzeitlichen) Alters für Lockerbraunerde-Substrat und Deckschutt (Decksediment).
Aus dem Gebiet der weichselzeitlichen Vereisung in Polen werden allgemein verbreitete geringmächtige periglaziale Deckschichten beschrieben. Sie zeigen in der Regel eine äolische Beeinflussung und unterscheiden sich dadurch vom Liegenden. Es handelt sich um spätglaziale Bildungen, wie sie aus dem Jungmoränengebiet der DDR seit langem bekannt sind. Ähnliche Substrate wurden auch im nördlichen Alpenvorland gefunden.
Im Lößprofil der Ziegelei Glos bei Lisieux ist eine Abfolge fossiler Boden aufgeschlossen, die sich gut mit der hessischen Lößstratigraphie verbinden läßt. Über dem letztinterglazialen Boden liegen nach einer Diskordanz der Lohner Boden, der E1-, der E2- und der E4-Naß-boden. Letzterer wird häufig als Äquivalent des „Sol de Kesselt" angesehen. Somit zeigt sich auch für dieses Gebiet, daß dieser Boden stratigraphisch nicht dem Lohner Boden entsprechen kann.
Un tuf volcanique a ete mis en evidence dans trois profils de loess de Hesbaye (Rocourt et Lixhe) et du Limbourg neerlandais (Nagelbeek). Ce tuf correspond probablement ä l'Eltviller Tuff connu en Hesse (SEMMEL 1967). En consequence, cette decouverte permet de comparer directement une partie de la sequence des loess du Pleistocene superieur propre ä chaque region
In der Monte Cavallo-Gruppe fand Verf. in Stauseesedimenten fossile Holzstücke, für die die 14 C-Datierung ein Alter von 29 350 ± 460 Jahren vor 1950 n. Chr. ergab. Die schluffigen Ablagerungen, die in etwa 900 m, fast 80 m über dem heutigen Flußbett des T. Caltea aufgeschlossen sind, ruhen auf Schottern und werden von Moräne überlagert.
Aufgrund seiner stratigraphischen Lage und seines 14C-datierten Alters kann das Holz (Picea abies bzw. Larix) einem zeitlichen Äquivalent des Paudorf-Interstadials zugeordnet werden. Dieser Fund von Großresten ermöglicht somit eine erste absolute Datierung des Paudorf-Interstadials für die Südalpen und Oberitalien.
Das Cranium eines fossilen Hominiden des Formenkreises Homo sapiens sapiens wurde relativ-geologisch sowie absolut durch Radiokohlenstoff und Aminosäuren auf ungefähr 31 000 Jahre B.P. datiert. Andere absolute sowie relative Daten an Mollusken und Mammutzähnen in überlagernden jüngeren Straten datieren auf 18 000 — 21000 und 16 000 Jahren B.P. Geomorphologische und geophysikalische Datierungen stimmen somit gut überein. Er ist der älteste datierte und früheste Bewohner Zentraleuropas, der dem Homo sapiens sapiens angehört.
Aus Franken wird die Entwicklung quartärer Hohlformen beschrieben, deren Rekonstruktion mit Hilfe lößstratigraphischer Methoden (fossile Böden, Tuffbänder, Umlagerungszonen etc.) möglich ist. Bei vielen Formen zeigt sich, daß sie bereits größere Vorläuferformen präwürmzeitlichen Alters hatten. Die Entwicklung während des Würms läßt sich an manchen Beispielen in besonders instruktiver Weise verfolgen. Zu Beginn des Würms, im unteren Mittelwürm und im unteren Jungwürm dominierte zeitweise die Abtragung und Verlagerung. Im oberen Mittelwürm sowie im oberen Jungwürm herrschte äolische Lößsedimentation vor. Diese Ergebnisse stimmen gut mit den bereits aus anderen mitteleuropäischen Lößgebieten bekannten Befunden überein. Mit dem Trockental-System von Helmstadt wird die Entwicklung von Hohlformen beschrieben, deren Anlage bis in das ältere Pleistozän zurückreicht.
In vorliegender Untersuchung wurde der Rißlöß zwischen der 1. und 2. fossilen Parabraunerde anhand schwächerer Bodenbildungen und eingeschalteter Abtragungsphasen zu gliedern versucht. Im jüngeren Riß herrschte starke Lößsedimentation vor, wobei es in mindestens 6 kaltfeuchten Abschnitten zur Ausbildung schwacher periglazialer Naßböden kam. Die Naßbodenserie wurde als Bruchköbeler Böden (B) bezeichnet. Im jüngsten Rißlöß ist wenige dm unter dem Eemboden als tephrochronologischer Leithorizont der Krifteler Tuff (vgl. SEMMEL 1968) eingeschaltet. Den mittleren Profilbereich im Rißlöß zeichnen feuchtere Klimaabschnitte mit starken Verschwemmungsphasen aus, die in den meisten Profilen zu erheblichen Diskordanzen geführt haben. An der Basis der wenigen kompletten Rißlöß-Profile treten vorwiegend in Hessen über der zumeist gekappten 2. fossilen Parabraunerde maximal zwei Schwarzerden auf, die von SEMMEL (1968) als Weilbacher Humuszonen bezeichnet werden. Unmittelbar über diesen Schwarzerden folgt die Ostheimer Zone, eine Fließerde aus aufgearbeitetem Solumaterial der liegenden Böden. Insgesamt zeigt die aus den Rißböden rekonstruierte Klimaabfolge — neben geringfügigen Abweichungen — überraschende Parallelen zur paläopedologisch-klimatischen Gliederung der Würmkaltzeit.
Crustal structure at the western end of the North Anatolian Fault Zone from deep seismic sounding
(2001)
The first deep seismic sounding experiment in Northwestern Anatolia was carried out in October 1991 as part of the "German - Turkish Project on Earthquake Prediction Research" in the Mudurnu area of the North Anatolian Fault Zone. The experiment was a joint enterprise by the Institute of Meteorology and Geophysics of Frankfurt University, the Earthquake Research Institute (ERI) in Ankara, and the Turkish Oil Company (TPAO). Two orthogonal profiles, each 120 km in length with a crossing point near Akyazi, were covered in succession by 30 short period tape recording seismograph stations with 2 km station spacing. 12 shots, with charge sizes between 100 and 250 kg, were fired and 342 seismograms out of 360 were used for evaluation. By coincidence an M b = 4.5 earthquake located below Imroz Island was also recorded and provided additional information on Moho and the sub-Moho velocity. A ray tracing method orginally developed by Weber (1986) was used for travel time inversion. From a compilation of all data two generalized crustal models were derived, one with velocity gradients within the layers and one with constant layer velocities. The latter consists of a sediment cover of about 2 km with V p » 3.6 km/s, an upper crystalline crust down to 13 km with V p » 5.9 km/s, a middle crust down to 25 km depth with V p » 6.5 km/s, a lower crust down to 39 km Moho depth with V p » 7.0 km/s and V p » 8.05 km/s below the Moho. The structure of the individual profiles differs slightly. The thickest sediment cover is reached in the Izmit-Sapanca-trough and in the Akyazi basin. Of particular interest is a step of about 4 km in the lower crust near Lake Sapanca and probably an even larger one in the Moho (derived from the Imroz earthquake data). After the catastrophic earthquake of Izmit on 17 August 1999 this significant heterogeneity in crustal structure appears in a new light with regard to the possible cause of the Izmit earthquake. Heterogeneities in structure are frequently also heterogeneities in strength and stress that impede or even lock rupture. The Izmit earthquake is discussed in relation to a large stepover or jog at the North Anatolian Fault.
Aim: Predicting future changes in species richness in response to climate change is one of the key challenges in biogeography and conservation ecology. Stacked species distribution models (S‐SDMs) are a commonly used tool to predict current and future species richness. Macroecological models (MEMs), regression models with species richness as response variable, are a less computationally intensive alternative to S‐SDMs. Here, we aim to compare the results of two model types (S‐SDMS and MEMs), for the first time for more than 14,000 species across multiple taxa globally, and to trace the uncertainty in future predictions back to the input data and modelling approach used.
Location: Global land, excluding Antarctica.
Taxon: Amphibians, birds and mammals.
Methods: We fitted S‐SDMs and MEMs using a consistent set of bioclimatic variables and model algorithms and conducted species richness predictions under current and future conditions. For the latter, we used four general circulation models (GCMs) under two representative concentration pathways (RCP2.6 and RCP6.0). Predicted species richness was compared between S‐SDMs and MEMs and for current conditions also to extent‐of‐occurrence (EOO) species richness patterns. For future predictions, we quantified the variance in predicted species richness patterns explained by the choice of model type, model algorithm and GCM using hierarchical cluster analysis and variance partitioning.
Results: Under current conditions, species richness predictions from MEMs and S‐SDMs were strongly correlated with EOO‐based species richness. However, both model types over‐predicted areas with low and under‐predicted areas with high species richness. Outputs from MEMs and S‐SDMs were also highly correlated among each other under current and future conditions. The variance between future predictions was mostly explained by model type.
Main conclusions: Both model types were able to reproduce EOO‐based patterns in global terrestrial vertebrate richness, but produce less collinear predictions of future species richness. Model type by far contributes to most of the variation in the different future species richness predictions, indicating that the two model types should not be used interchangeably. Nevertheless, both model types have their justification, as MEMs can also include species with a restricted range, whereas S‐SDMs are useful for looking at potential species‐specific responses.
This study reports and discusses new radiometric ages, petrographical and volcanological observations and whole rock geochemical data of the rocks of the Rudnik Mts. volcano-intrusive complex. The complex hosts a Pb-Zn-Ag deposit and belongs to the Serbo-Macedonian metallogenetic belt. Two distinct igneous events are distignuished. The first occurred >30 Ma and was mainly characterized by extrusive and shallow intrusive dacites and andesites and was unrelated to mineralization. The second igneous event occurred <23 Ma and was highly heterogeneous in terms of volcanic products and petrographic varieties, but with predominance of quartzlatites. The dacite-andesites (first event) and the quartzlatites (second event) are geochemically similar and display a calc-alkaline affinity and highly incompatible element enriched patterns on spider diagrams, but the younger quartzlatites are richer in K2O, Rb and Ba and poorer in Sr. This is taken as evidence that mixing between an ultrapotassic lamprophyre/lamproite magma and an acid calc-alkaline (dacite-like) magma was essential petrogenetic processes during the second event. The proposed simplified volcanological model suggests that this mixing was responsible for triggering strongly explosive volcanic activity as well as for providing conditions for active hydrothermal and mineralization processes. The observed link between a specific magmatic phase and ore deposit formation can be a general phennomenon in the Balkans, and must be addressed by further and more advanced studies.
This paper provides new geochemical data focusing on valuable elements in the coal, parting, and floor samples in the No. 5 coal seam of the Taiyuan Formation from the Wujiawan mine, Datong coalfield, northern China. The minerals mainly consist of kaolinite, calcite, and pyrite, as well as trace amounts of quartz and illite. The No. 5 coal is enriched in Li, Ga, high field strength elements (HFSEs), and rare earth elements and yttrium (REY) when compared with world hard coals. Of particular interest is the high average concentration of Li (67.66 μg/g), which is around seven times higher than the value for world hard coals. Lithium, Ga, and HFSEs have strong inorganic affinities, whereas REY have organic affinities. The main carrier of Li, Ga, and HFSEs is aluminosilicate minerals, while REY appear to occur with organophosphorus. These HFSEs are enriched, both in the parting and in the adjacent coal samples. This suggests that these elements are likely to leach out during the diagenetic process. The distribution patterns of REY, along with the ratio of Al2O3/TiO2 and the figure of Zr/TiO2 vs. Nb/Y are suggestive of their derivation from felsic parent material. In the northern and eastern part of the Datong coalfield, there are several regions where the Li content is higher than the mineable grade, in particular in the northern Datong coalfield where there is a mine with an Li content of 294.6 μg/g. This is significantly higher than the mineable grade. Therefore, there is a potential for financially viable recovery of Li in these coals of the Datong coalfield.
The Early Permian coal is of great value in the Tengxian Coalfield, Shandon Province, Eastern China. This work deals with the new data focusing on mineralogical characteristics in the Early Permian Shanxi Formation No. 3 coal from the Jinyuan Mine. The Jinyuan coal is a low ash and highly volatile A bituminous coal. Minerals in the No. 3 coal mainly comprise of kaolinite, ankerite, illite, calcite, siderite, and quartz, with varying compositions of trace amounts of pyrite, jarosite, bassanite, anatase, and rutile. According to mineral assemblage in the coal plies, three Types (A to C) can be identified in the No. 3 coal. The dominant minerals in Type A are poorly-ordered kaolinite, illite, quartz, pyrite, and jarosite. Type B is mainly composed of well-ordered kaolinite, illite, siderite, ankerite, and calcite. Type C, with just one sample (JY-3-7c), which contains high proportions of calcite (54%) and ankerite (34%). Terrigenous minerals are elevated in coal plies that typically have relatively high contents of ash yield. The formation of syngenetic pyrite was generally due to seawater, while the sulphate minerals (jarosite and coquimbite) were derived from the oxidation of pyrite. Epigenetic vein-like or fracture-fillings carbonate minerals (ankerite, calcite, and siderite), kaolinite, and pyrite, as well as authigenic quartz were derived from the influx of hydrothermal fluids during different periods, from the authigenic to epigenetic. The paragonite in the coal may have been formed by the precipitated from Na-rich hydrothermal fluids. No effects of magmatic intrusion on mineralogy were investigated in this research.
Background: Point of care devices for performing targeted coagulation substitution in bleeding patients have become increasingly important in recent years. New on the market is the Quantra® from HemoSonics (LC, Charlottesville, VA, US). It uses sonorheometry, a sonic estimation of elasticity via resonance (SEER), a novel ultrasound-based technology that measures viscoelastic properties of whole blood. Several studies have already shown the comparability with devices already established on the market such as the ROTEM® (TEM International GmbH, Munich, Germany).
Objective: In contrast to existing studies, the planned study will be the first prospective interventional study using the new Quantra® system in a cardiac surgical patient cohort. The aim is to investigate the non-inferiority between an already existing coagulation algorithm, based on ROTEM®/Multiplate®, and a new algorithm based on the Quantra®, for the treatment of coagulopathic cardiac surgical patients.
Methods: The study is divided into two phases. In an initial observation phase, whole blood samples of 20 patients will be analyzed using both ROTEM®/Multiplate® and Quantra® obtained at three defined points of time (prior to surgery, after completion of cardiopulmonary bypass, on arrival in the intensive care unit). The obtained threshold values will be used to create an algorithm for hemotherapy. In a second intervention phase, the new algorithm will be tested against an algorithm used routineously for years at our department for non-inferiority.
Results: The main objective of the examination is the cumulative loss of blood within 24 hours after surgery. Statistical calculations based on literature and in-house data suggest that the new algorithm is not inferior if the difference in cumulative blood loss is < 150ml/24 h.
Conclusions: Because of the comparability of the Quantra® sonorheometry system with ROTEM® rotational thromboelastometric measurement methods, the existing hemotherapy treatment algorithm can be adapted to the Quantra device with a proof of non-inferiority. Clinical Trial: International Registered Report Identifier (IRRID): clinicaltrials.gov: NCT03902275
Inclusions of breyite (previously known as walstromite-structured CaSiO3) in diamond are usually interpreted as retrogressed CaSiO3 perovskite trapped in the transition zone or the lower mantle. However, the thermodynamic stability field of breyite does not preclude its crystallization together with diamond under upper-mantle conditions (6–10 GPa). The possibility of breyite forming in subducted sedimentary material through the reaction CaCO3 + SiO2 = CaSiO3 + C + O2 was experimentally evaluated in the CaO–SiO2–C–O2 ± H2O system at 6–10 GPa, 900–1500 ∘C and oxygen fugacity 0.5–1.0 log units below the Fe–FeO (IW) buffer. One experimental series was conducted in the anhydrous subsystem and aimed at determining the melting temperature of the aragonite–coesite (or stishovite) assemblage. It was found that melting occurs at a lower temperature (∼1500 ∘C) than the decarbonation reaction, which indicates that breyite cannot be formed from aragonite and silica under anhydrous conditions and an oxygen fugacity above IW – 1. In the second experimental series, we investigated partial melting of an aragonite–coesite mixture under hydrous conditions at the same pressures and redox conditions. The melting temperature in the presence of water decreased strongly (to 900–1200 ∘C), and the melt had a hydrous silicate composition. The reduction of melt resulted in graphite crystallization in equilibrium with titanite-structured CaSi2O5 and breyite at ∼1000 ∘C. The maximum pressure of possible breyite formation is limited by the reaction CaSiO3 + SiO2 = CaSi2O5 at ∼8 GPa. Based on the experimental results, it is concluded that breyite inclusions found in natural diamond may be formed from an aragonite–coesite assemblage or carbonate melt at 6–8 GPa via reduction at high water activity.
The crystal structure of MgCO3-II has long been discussed in the literature where DFT-based model calculations predict a pressure-induced transition of the carbon atom from the sp2 to the sp3 type of bonding. We have now determined the crystal structure of iron-bearing MgCO3-II based on single-crystal X-ray diffraction measurements using synchrotron radiation. We laser-heated a synthetic (Mg0.85Fe0.15)CO3 single crystal at 2500 K and 98 GPa and observed the formation of a monoclinic phase with composition (Mg2.53Fe0.47)C3O9 in the space group C2/m that contains tetrahedrally coordinated carbon, where CO44− tetrahedra are linked by corner-sharing oxygen atoms to form three-membered C3O96− ring anions. The crystal structure of (Mg0.85Fe0.15)CO3 (magnesium iron carbonate) at 98 GPa and 300 K is reported here as well. In comparison with previous structure-prediction calculations and powder X-ray diffraction data, our structural data provide reliable information from experiments regarding atomic positions, bond lengths, and bond angles.
Stability of halocarbons in whole air samples from the upper
troposphere and lowermost stratosphere
(2019)
Measurements of halogenated hydrocarbons of ambient air frequently rely on canister sampling followed by offline laboratory analysis. This allows for a large number of compounds to be analysed under stable conditions, maximising measurement precision. However, individual compounds might be affected during storage of canister samples. In order to assess halocarbon stability in whole air samples from the upper troposphere and lowermost stratosphere, we performed stability tests using the air sampling unit High REsolution Sampler (HIRES) which is part of the CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container) instrument package. HIRES holds 88 light-weight stainless steel cylinders that are pressurized in flight to 4.5 bar using metal bellows pumps. The HIRES sampling unit was first deployed in 2010, but has up to now not been used for regular halocarbon analysis with exception of chloromethane. The sample collection unit was tested for sampling and storage effects of 28 halogenated compounds. The focus was on compound stability in the stainless steel canisters during storage of up to five weeks and on the influence of ozone, since flights take place in the upper troposphere and lowermost stratosphere with ozone mixing ratios of up to several hundred ppbV. Most of the investigated (hydro)chlorofluorocarbons and long-lived hydrofluorocarbons were found to be stable over a storage time of up to five weeks and were unaltered by ozone being present during pressurization. Some compounds such as for example dichloromethane, trichloromethane and tetrachloroethene started to decrease in the canisters after a storage time of more than two weeks or exhibited lowered mixing ratios in samples pressurized with ozone present. Few compounds such as for example tetrachloromethane and tribromomethane were found to be not stable in the HIRES stainless-steel canisters independent of ozone levels. Also growth was observed during storage, namely for HFC-152a and HFC-23.
Measurements of halogenated trace gases in ambient air frequently rely on canister sampling followed by offline laboratory analysis. This allows for a large number of compounds to be analysed under stable conditions, maximizing measurement precision. However, individual compounds might be affected during the sampling and storage of canister samples. In order to assess halocarbon stability in whole-air samples from the upper troposphere and lowermost stratosphere, we performed stability tests using the high-resolution sampler (HIRES) air sampling unit, which is part of the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) instrument package. The HIRES unit holds 88 lightweight stainless-steel cylinders that are pressurized in flight to 4.5 bar using metal bellows pumps. The HIRES unit was first deployed in 2010 but has up to now not been used for regular halocarbon analysis with the exception of chloromethane analysis. The sample collection unit was tested for the sampling and storage effects of 28 halogenated compounds. The focus was on compound stability in the stainless-steel canisters during storage of up to 5 weeks and on the influence of ozone, since flights take place in the upper troposphere and lowermost stratosphere with ozone mixing ratios of up to several hundred parts per billion by volume (ppbv). Most of the investigated (hydro)chlorofluorocarbons and long-lived hydrofluorocarbons were found to be stable over a storage time of up to 5 weeks and were unaltered by ozone being present during pressurization. Some compounds such as dichloromethane, trichloromethane, and tetrachloroethene started to decrease in the canisters after a storage time of more than 2 weeks or exhibited lowered mixing ratios in samples pressurized with ozone present. A few compounds such as tetrachloromethane and tribromomethane were found to be unstable in the HIRES stainless-steel canisters independent of ozone levels. Furthermore, growth was observed during storage for some species, namely for HFC-152a, HFC-23, and Halon 1301.
A list of authors and their affiliations appears at the end of the paper New-particle formation is a major contributor to urban smog, but how it occurs in cities is often puzzling. If the growth rates of urban particles are similar to those found in cleaner environments (1–10 nanometres per hour), then existing understanding suggests that new urban particles should be rapidly scavenged by the high concentration of pre-existing particles. Here we show, through experiments performed under atmospheric conditions in the CLOUD chamber at CERN, that below about +5 degrees Celsius, nitric acid and ammonia vapours can condense onto freshly nucleated particles as small as a few nanometres in diameter. Moreover, when it is cold enough (below −15 degrees Celsius), nitric acid and ammonia can nucleate directly through an acid–base stabilization mechanism to form ammonium nitrate particles. Given that these vapours are often one thousand times more abundant than sulfuric acid, the resulting particle growth rates can be extremely high, reaching well above 100 nanometres per hour. However, these high growth rates require the gas-particle ammonium nitrate system to be out of equilibrium in order to sustain gas-phase supersaturations. In view of the strong temperature dependence that we measure for the gas-phase supersaturations, we expect such transient conditions to occur in inhomogeneous urban settings, especially in wintertime, driven by vertical mixing and by strong local sources such as traffic. Even though rapid growth from nitric acid and ammonia condensation may last for only a few minutes, it is nonetheless fast enough to shepherd freshly nucleated particles through the smallest size range where they are most vulnerable to scavenging loss, thus greatly increasing their survival probability. We also expect nitric acid and ammonia nucleation and rapid growth to be important in the relatively clean and cold upper free troposphere, where ammonia can be convected from the continental boundary layer and nitric acid is abundant from electrical storms.
Micromorphology is a suitable method to study the contents and stratigraphic relationships of pit fills. Within the ramparts of Corneşti-Iarcuri, fill layers of a pit were sampled. Th e pit fill was macroscopically divided into primary and secondary fill due to striking differences. These differences could be verified and concretized micromorphologically.
Diamond formation in the Earth has been extensively discussed in recent years on the basis of geochemical analysis of natural materials, high-pressure experimental studies, or theoretical aspects. Here, we demonstrate experimentally for the first time, the spontaneous crystallization of diamond from CH4-rich fluids at pressure, temperature and redox conditions approximating those of the deeper parts of the cratonic lithospheric mantle (5-7 GPa) without using diamond seed crystals or carbides. In these experiments the fluid phase is nearly pure methane, even though the oxygen fugacity was significantly above metal saturation. We propose several previously unidentified mechanisms that may promote diamond formation under such conditions and which may also have implications for the origin of sublithospheric diamonds. These include the hydroxylation of silicate minerals like olivine and pyroxene, H2 incorporation into these phases and the "etching" of graphite by H2 and CH4 and reprecipitation as diamond. This study also serves as a demonstration of our new high-pressure experimental technique for obtaining reduced fluids, which is not only relevant for diamond synthesis, but also for investigating the metasomatic origins of diamond in the upper mantle, which has further implications for the deep carbon cycle.
The frequency of extreme events has changed, having a direct impact on human lives. Regional climate models help us to predict these regional climate changes. This work presents an atmosphere–ocean coupled regional climate system model (RCSM; with the atmospheric component COSMO-CLM and the ocean component NEMO) over the European domain, including three marginal seas: the Mediterranean, North, and Baltic Sea. To test the model, we evaluate a simulation of more than 100 years (1900–2009) with a spatial grid resolution of about 25 km. The simulation was nested into a coupled global simulation with the model MPI-ESM in a low-resolution configuration, whose ocean temperature and salinity were nudged to the ocean–ice component of the MPI-ESM forced with the NOAA 20th Century Reanalysis (20CR). The evaluation shows the robustness of the RCSM and discusses the added value by the coupled marginal seas over an atmosphere-only simulation. The coupled system is stable for the complete 20th century and provides a better representation of extreme temperatures compared to the atmosphere-only model. The produced long-term dataset will help us to better understand the processes leading to meteorological and climate extremes.
The most frequently used boundary-layer turbulence parameterization in numerical weather prediction (NWP) models are turbulence kinetic energy (TKE) based-based schemes. However, these parameterizations suffer from a potential weakness, namely the strong dependence on an ad-hoc quantity, the so-called turbulence length scale. The physical interpretation of the turbulence length scale is difficult and hence it cannot be directly related to measurements or large eddy simulation (LES) data. Consequently, formulations for the turbulence length scale in basically all TKE schemes are based on simplified assumptions and are model-dependent. A good reference for the independent evaluation of the turbulence length scale expression for NWP modeling is missing. Here we propose a new turbulence length scale diagnostic which can be used in the gray zone of turbulence without modifying the underlying TKE turbulence scheme. The new diagnostic is based on the TKE budget: The core idea is to encapsulate the sum of the molecular dissipation and the cross-scale TKE transfer into an effective dissipation, and associate it with the new turbulence length scale. This effective dissipation can then be calculated as a residuum in the TKE budget equation (for horizontal sub-domains of different sizes) using LES data. Estimation of the scale dependence of the diagnosed turbulence length scale using this novel method is presented for several idealized cases.
Metasomatic evolution of coesite-bearing diamondiferous eclogite from the Udachnaya Kimberlite
(2020)
A coesite-bearing diamondiferous eclogite from the Udachnaya kimberlite (Daldyn field, Siberian craton) has been studied to trace its complex evolution recorded in rock-forming and minor mineral constituents. The eclogite sample is composed of rock-forming omphacite (60 vol%), garnet (35 vol%) and quartz/coesite (5 vol%) and contains intergranular euhedral zoned olivine crystals, up to 200 µm long, coexisting with phlogopite, orthopyroxene, clinopyroxene (secondary), K-feldspar, plagioclase, spinel, sodalite and djerfisherite. Garnet grains are zoned, with a relatively homogeneous core and a more magnesian overgrowth rim. The rim zones further differ from the core in having higher Zr/Y (6 times that in the cores), ascribed to interaction with, or precipitation from, a kimberlite-related melt. Judging by pressure-temperature estimates (~1200 °C; 6.2 GPa), the xenolith originated at depths of ~180–200 km at the base of the continental lithosphere. The spatial coexistence of olivine, orthopyroxene and coesite/quartz with K-Na-Cl minerals in the xenolith indicates that eclogite reacted with a deep-seated kimberlite melt. However, Fe-rich olivine, orthopyroxene and low-pressure minerals (sodalite and djerfisherite) likely result from metasomatic reaction at shallower depths during transport of the eclogite by the erupting kimberlite melt. Our results demonstrate that a mixed eclogitic-peridotitic paragenesis, reported previously from inclusions in diamond, can form by interaction of eclogite and a kimberlite-related melt.
Vegetation responds to drought through a complex interplay of plant hydraulic mechanisms, posing challenges for model development and parameterization. We present a mathematical model that describes the dynamics of leaf water-potential over time while considering different strategies by which plant species regulate their water-potentials. The model has two parameters: the parameter λ describing the adjustment of the leaf water potential to changes in soil water potential, and the parameter Δψww describing the typical ‘well-watered’ leaf water potentials at non-stressed (near-zero) levels of soil water potential. Our model was tested and calibrated on 110 time-series datasets containing the leaf- and soil water potentials of 66 species under drought and non-drought conditions. Our model successfully reproduces the measured leaf water potentials over time based on three different regulation strategies under drought. We found that three parameter sets derived from the measurement data reproduced the dynamics of 53% of an drought dataset, and 52% of a control dataset [root mean square error (RMSE) < 0.5 MPa)]. We conclude that, instead of quantifying water-potential-regulation of different plant species by complex modeling approaches, a small set of parameters may be sufficient to describe the water potential regulation behavior for large-scale modeling. Thus, our approach paves the way for a parsimonious representation of the full spectrum of plant hydraulic responses to drought in dynamic vegetation models.
Inappropriate land management leads to soil loss with destruction of the land’s resource and sediment input into the receiving river. Part of the sediment budget of a catchment is the estimation of soil loss. In the Ruzizi catchment in the Eastern Democratic Republic of the Congo (DRC), only limited research has been conducted on soil loss mainly dealing with local observations on geomorphological forms or river load measurements; a regional quantification of soil loss is missing so far. Such quantifications can be calculated using the Universal Soil Loss Equation (USLE). It is composed of four factors: precipitation (R), soil (K), topography (LS), and vegetation cover (C). The factors can be calculated in different ways according to the characteristics of the study area. In this paper, different approaches for calculating the single factors are reviewed and validated with field work in two sub-catchments of Ruzizi River supplying the water for the reservoirs of Ruzizi I and II hydroelectric dams. It became obvious that the (R)USLE model provides the best results with revised R and LS factors. C factor calculations required to conduct a supervised classification using the Maximum Likelihood Procedure. Different C factor values were assigned to the land cover classes. The calculations resulted in a soil loss rate for the predominantly occurring Ferralsols and Leptosols of around 576 kt/yr in both catchments, when 2016 landcover and precipitation are used. This represents an area-normalized value of 40.4 t/ha/yr for Ruzizi I and 50.5 t/ha/yr for Ruzizi II due to different landcover in the two sub-catchments. The mean value for the whole study area is 47.8 t/ha/yr or even 27.1 t/ha/yr when considering land management techniques like terracing on the slopes (P factor). This work has shown that the (R)USLE model can serve as an easy to handle tool for soil loss quantification when comprehensive field work results are sparse. The model can be implemented in Geographic Information Systems (GIS) with free data; hence, a validation is crucial. It becomes apparent that the use of high resolution Sentinel 2a MSI data as the basis for C factor calculations is an appropriate method for considering heterogeneous Land Use Land Cover (LULC) patterns. To transfer the approach to other regions, the calculation of factor R needs to be modified
Accretion rates of Holocene tropical coral reefs in three areas in the Atlantic, Pacific and Indian Oceans have been quantified in 79 dated core sections in 34 reef cores from Belize, the Maldives and French Polynesia. Holocene vertical reef accretion rate averages 5.05 m/kyr and has decreased during the past 10 kyr. Accretion rates in branched and massive coral facies are statistically similar. Reef accretion rate is positively correlated with the rate of sea‐level rise, that is the degree of creation of accommodation space, and with climate as expressed in a Holocene sea surface temperature anomaly. Accommodation space is also created by subsidence, but at a rate one to two orders of magnitude lower than that created by glacio‐eustasy (0.04 to 0.16 m/kyr). Lagoonal background sedimentation in adjacent reef lagoons averages 0.89 m/kyr as measured in 72 dated core sections in 28 cores. Lagoonal carbonate sedimentation on top of underlying mangrove peat usually starts after a considerable hiatus of ca 3 kyr on average. The lagoonal background sedimentation rate increased during the Holocene, probably due to deepening. The differences between vertical reef accretion and lagoonal background sedimentation rates are a major factor in the production of the widely known saucer shapes typical of tropical reefs and carbonate platforms, that is the creation of unfilled accommodation space. Reef core recovery, used as a proxy for reef consolidation, and core depth exhibit a statistically negative correlation based on data from 326 core barrels. Recovery and marine cement abundance (average volume 8.6%) also decrease from windward to leeward core positions. These observations are presumably a result of both a decrease in the rate of sea‐level rise that is the increase in time available for submarine cementation during the Holocene and the amount of flushing of reef interstices by marine waters.
Diurnal valley winds frequently form over complex topography, particularly under fair weather conditions, and have a significant impact on the local weather and climate. Since diurnal valley winds result from complex and multi-scale interactions, their representation in numerical weather prediction models is challenging. Better understanding of these local winds based on observations is crucial to improve the accuracy of the forecasts. This study investigates the diurnal evolution of the three-dimensional mean wind structure in a deep Alpine valley, the Rhone valley at Sion, using data from a radar wind profiler and a surface weather station operated continuously from 1 September 2016 to 17 July 2017. In particular, the wind profiler data was analyzed for a subset of days on which fair weather conditions allowed for the full development of thermally driven winds. A pronounced diurnal cycle of the wind speed, as well as a reversal of the wind direction twice per day is documented for altitudes up to about 2 km above ground level (AGL) in the warm season and less than 1 km AGL in winter. The diurnal pattern undergoes significant changes during the course of the year. Particularly during the warm-weather months of May through to September, a low-level wind maximum occurs, where mean maximum up-valley velocities of 8–10 m s−1 are found between 15–16 UTC at altitudes around 200 m AGL. In addition, during nighttime, a down-valley jet with maximum wind speeds of 4–8 m s−1 around 1 km AGL is found. A case study of a three-day period in September 2016 illustrates the occurrence of an elevated layer of cross-valley flow around 1–1.5 km AGL.
Cenozoic lignite deposits are widespread across Europe, Asia, America, Australia, and Indonesia. These deposits were the subject of numerous studies on changes in regional/global paleoclimates, paleobotany, paleoenvironment, and basin evolutions, which led to the formation of these lignites. In some of these Cenozoic lignite deposit basins, a succession of pale and dark lignite layers has been described in the Miocene Lower Rhine Basin in Germany, the Oligo-Miocene Gippsland Basin in southeastern Australia, and several Mio-Pliocene basins in southwestern China. Furthermore, pale and dark lithotypes in lignite seams also have been found in some Pliocene lignite deposit basins from Slovenia, Serbia, and Poland. The widespread cyclic occurrence of pale and dark layers in lignite basins might represent alternating depositional conditions related to the changes in plant communities, the regional/global climate, the tectonic setting, the Asian monsoon, and orbital periodicity during peat formation. ...
Under the Kigali Amendment to the Montreal Protocol, new controls are being implemented to reduce emissions of HFC-23 (CHF3), a by-product during the manufacture of HCFC-22 (CHClF2). Starting in 2015, China and India, who dominate global HCFC-22 production (75% in 2017), set out ambitious programs to reduce HFC-23 emissions. Here, we estimate that these measures should have seen global emissions drop by 87% between 2014 and 2017. Instead, atmospheric observations show that emissions have increased and in 2018 were higher than at any point in history (15.9 ± 0.9 Gg yr−1). Given the magnitude of the discrepancy between expected and observation-inferred emissions, it is likely that the reported reductions have not fully materialized or there may be substantial unreported production of HCFC-22, resulting in unaccounted-for HFC-23 by-product emissions. The difference between reported and observation-inferred estimates suggests that an additional ~309 Tg CO2-equivalent emissions were added to the atmosphere between 2015 and 2017.
Groundwater is the largest source of accessible freshwater with its dynamics having significantly changed due to human withdrawals, and being projected to continue to as a result of climate change. The pumping of groundwater has led to lowered water tables, decreased base flow, and depletion.
Global hydrological models (GHMs) are used to simulate the global freshwater cycle, assessing impacts of changes in climate and human freshwater use. Currently, groundwater is commonly represented by a bucket-like linear storage component in these models. Bucket models, however, cannot provide information on the location of the groundwater table. Due to this limitation, they can only simulate groundwater discharge to surface water bodies but not recharge from surface water to groundwater and calculate no lateral and vertical groundwater flow whatsoever among grid cells. For instance this may lead to an underestimation of groundwater resources in semiarid areas, where groundwater is often replenished by surface water. In order to overcome these limitations it is necessary to replace the linear groundwater model in GHMs with a hydraulic head gradient-based groundwater flow model
This thesis presents the newly developed global groundwater model G3M and its coupling to the GHM WaterGAP spanning over 70,000 lines of newly developed code. Development and validation of the modeling software are discussed along with numerical challenges. Based on the newly developed software, a global natural equilibrium groundwater model is presented showing better agreements with observations than previous models. Groundwater discharge to rivers is found to be the most dominant flow component globally, compared to flows to other surface water bodies and lateral flows. Furthermore, first global maps of the distribution of gaining and losing surface water bodies are displayed.
For the purpose of determining the uncertainty in model outcomes a sensitivity study is conducted with an innovative approach through applying a global sensitivity analysis for a computationally complex model. First global maps of spatially distributed parameter sensitivities are presented. The results at hand indicate that globally simulated hydraulic heads are equally sensitive to hydraulic conductivity, groundwater recharge and surface water body elevation, even though parameter sensitivities do vary regionally.
A high resolution model of New Zealand is developed to further understand the involved uncertainties connected to the spatial resolution of the global model. This thesis finds that a new understanding is necessary how these models can be evaluated and that a simple increase in spatial resolution is not improving the model performance when compared to observations.
Alongside the assessment of the natural equilibrium, the concept of a fully coupled transient model as integrated storage component replacing the former model in the hydrological model WaterGAP is discussed. First results reveal that the model shows reasonable response to seasonal variability although it contains persistent head trends leading to global overestimates of water table depth due to an incomplete coupling. Nonetheless, WaterGAP-G3M is already able to show plausible long term storage trends for areas that are known to be affected by groundwater depletion. In comparison with two established regional models in the Central Valley the coupled model shows a highly promising simulation of storage declines.