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The current study tested the assumption that floristic and functional diversity patterns are negatively related to soil nitrogen content. We analyzed 20 plots with soil N-contents ranging from 0.63% to 1.06% in a deciduous forest near Munich (Germany). To describe species adaptation strategies to different nitrogen availabilities, we used a plant functional type (PFT) approach. Each identified PFT represents one realized adaptation strategy to the current environment. These were correlated, next to plant species richness and evenness, to soil nitrogen contents. We found that N-efficient species were typical for low soil nitrogen contents, while N-requiring species occur at high N-contents. In contrast to our initial hypotheses, floristic and functional diversity measures (number of PFTs) were positively related to nitrogen content in the soil. Every functional group has its own adaptation to the prevailing environmental conditions; in consequence, these functional groups can co-exist but do not out-compete one another. The increased number of functional groups at high N-contents leads to increased species richness. Hence, for explaining diversity patterns we need to consider species groups representing different adaptations to the current environmental conditions. Such co-existing ecological strategies may even overcome the importance of competition in their effect on biodiversity.
ucleation experiments starting from the reaction of OH radicals with SO2 have been performed in the IfT-LFT flow tube under atmospheric conditions at 293±0.5 K for a relative humidity of 13–61%. The presence of different additives (H2, CO, 1,3,5-trimethylbenzene) for adjusting the OH radical concentration and resulting OH levels in the range (4–300)·105 molecule cm−3 did not influence the nucleation process itself. The number of detected particles as well as the threshold H2SO4 concentration needed for nucleation was found to be strongly dependent on the counting efficiency of the used counting devices. High-sensitivity particle counters allowed the measurement of freshly nucleated particles with diameters down to about 1.5 nm. A parameterization of the experimental data was developed using power law equations for H2SO4 and H2O vapour. The exponent for H2SO4 from different measurement series was in the range of 1.7–2.1 being in good agreement with those arising from analysis of nucleation events in the atmosphere. For increasing relative humidity, an increase of the particle number was observed. The exponent for H2O vapour was found to be 3.1 representing a first estimate. Addition of 1.2·1011 molecule cm−3 or 1.2·1012 molecule cm−3 of NH3 (range of atmospheric NH3 peak concentrations) revealed that NH3 has a measureable, promoting effect on the nucleation rate under these conditions. The promoting effect was found to be more pronounced for relatively dry conditions. NH3 showed a contribution to particle growth. Adding the amine tert-butylamine instead of NH3, the enhancing impact for nucleation and particle growth appears to be stronger.
Nucleation experiments starting from the reaction of OH radicals with SO2 have been performed in the IfT-LFT flow tube under atmospheric conditions at 293±0.5 K for a relative humidity of 13–61%. The presence of different additives (H2, CO, 1,3,5-trimethylbenzene) for adjusting the OH radical concentration and resulting OH levels in the range (4–300) ×105 molecule cm -3 did not influence the nucleation process itself. The number of detected particles as well as the threshold H2SO4 concentration needed for nucleation was found to be strongly dependent on the counting efficiency of the used counting devices. High-sensitivity particle counters allowed the measurement of freshly nucleated particles with diameters down to about 1.5 nm. A parameterization of the experimental data was developed using power law equations for H2SO4 and H2O vapour. The exponent for H2SO4 from different measurement series was in the range of 1.7–2.1 being in good agreement with those arising from analysis of nucleation events in the atmosphere. For increasing relative humidity, an increase of the particle number was observed. The exponent for H2O vapour was found to be 3.1 representing an upper limit. Addition of 1.2×1011 molecule cm -3 or 1.2×1012 molecule cm -3 of NH3 (range of atmospheric NH3 peak concentrations) revealed that NH3 has a measureable, promoting effect on the nucleation rate under these conditions. The promoting effect was found to be more pronounced for relatively dry conditions, i.e. a rise of the particle number by 1–2 orders of magnitude at RH = 13% and only by a factor of 2–5 at RH = 47% (NH3 addition: 1.2×1012 molecule cm -3). Using the amine tert-butylamine instead of NH3, the enhancing impact of the base for nucleation and particle growth appears to be stronger. Tert-butylamine addition of about 1010 molecule cm -3 at RH = 13% enhances particle formation by about two orders of magnitude, while for NH3 only a small or negligible effect on nucleation in this range of concentration appeared. This suggests that amines can strongly influence atmospheric H2SO4-H2O nucleation and are probably promising candidates for explaining existing discrepancies between theory and observations.
Auf der Suche nach Erfahrungen in den Tropen setzte der Geografiestudent Jürgen Runge das erste Mal in Togo seinen Fuß auf den afrikanischen Kontinent. Aus einem etwas holprigen Start wurde eine große Zuneigung zu Zentral- und Westafrika. Heute ist Runge Direktor des Zentrums für Interdisziplinäre Afrikaforschung an der Goethe-Universität und forscht gemeinsam mit Partnern der Region vor allem zu Landschaftsentwicklung, Flusssedimenten und Klimawandel.
The main objective of the study presented in this paper was to develop an evaluation scheme which is suitable for spatially explicit groundwater vulnerability assessment according to the Water Framework Directive (WFD). Study area was the Hase river catchment, an area of about 3 000 km2 in north-west Germany which is dominated by livestock farming, in particular pig and poultry production. For the Hase river catchment, the first inventory of the WFD led to the conclusion that 98% of the catchment area is "unclear/unlikely" to reach a good groundwater status due to diffuse nitrogen emissions from agriculture. The groundwater vulnerability assessment was embedded in the PartizipA project ("Participative modelling, Actor and Ecosystem Analysis in Regions with Intensive Agriculture", www.partizipa.net), within which a so-called actors´ platform was established in the study area. The objective of the participatory process was to investigate the effects of the WFD on agriculture as well as to discuss groundwater protection measures which are suitable for an integration in the programme of measures. The study was conducted according to the vulnerability assessment concept of the Intergovernmental Panel on Climate Change, considering sensitivity, exposure and adaptive capacity. Sensitivity was computed using the DRASTIC index of natural groundwater pollution potential. Exposure (for a reference scenario) was computed using the STOFFBILANZ nutrient model. Several regional studies were analysed to evaluate the adaptive capacity. From these studies it was concluded that the adaptive capacity in the Hase river catchment is very low due to the economic importance of the agricultural sector which will be significantly affected by groundwater protection measures. As a consequence, the adaptive capacity was not considered any more in the vulnerability assessment. A groundwater vulnerability evaluation scheme is presented which enjoys the advantage that both exposure and sensitivity can be operationalized in a spatially resolved manner (500×500 m grid) by the two models mentioned above. The evaluation scheme was applied in the Hase river catchment. 21% of the catchment was classified as highly vulnerable, another 73% as medium vulnerable. Only 6% of the Hase river catchment has low vulnerability. Grid cells of the high vulnerability class are considered as priority areas for groundwater protection measures in the programme of measures of the WFD. Measures will be particularly effective in the north-eastern part of the catchment where groundwater vulnerability is mainly due to high nitrogen emissions.
An evaluation scheme is presented in this paper which can be used to assess groundwater vulnerability according to the requirements of the European Water Framework Directive (WFD). The evaluation scheme results in a groundwater vulnerability map identifying areas of high, medium and low vulnerability, as necessary for the measurement planning of the WFD. The evaluation scheme is based on the definition of the vulnerability of the Intergovernmental Panel on Climate Change (IPCC). It considers exposure, sensitivity and the adaptive capacity of the region. The adaptive capacity is evaluated in an actors' platform, which was constituted for the region in the PartizipA ("Participative modelling, Actor and Ecosystem Analysis in Regions with Intensive Agriculture") project. As a result of the vulnerability assessment, 21% of the catchment area was classified as being highly vulnerable, whereas 73% has medium vulnerability and 6% has low vulnerability. Thus, a groundwater vulnerability assessment approach is presented, which can be used in practice on a catchment scale for the WFD measurement planning.
Aus der Notwendigkeit heraus, "nachhaltig die Funktionen des Bodens zu sichern" (§1 BBodSchG), und damit auch Bodenschutz vorsorgend in Planungsprozesse zu integrieren, wurde ein neues Bodenschutzkonzept entwickelt. Es basiert auf einer differenzierten, aber gleichzeitig nachvollziehbaren Bodenbewertung. Das Problem bei der Bodenbewertung ist, dass etwas bewertet werden soll, für das - je nach Fragestellung - immer wieder neue Ziele definiert werden müssen. Deshalb liegt der Bodenbewertung ein Zielsystem zu Grunde, das Schutzziele klar festlegt und mit Hilfe dessen die Bodenbewertung nachvollziehbar wird. Für das Bodenschutzkonzept werden aus der Vielzahl möglicher Kriterien wichtige vorgestellt, aus denen die - bezogen auf dieses Zielsystem - wesentlichen ausgewählt werden können. Um aussagekräftige Daten für diese Kriterien zu erhalten stützt sich die Bodenbewertung auf bodenkundliche sowie landschaftsgenetisch-geomorphologische Zusammenhänge. Die eigentliche Bewertung erfolgt dann in drei Schritten: zuerst eine Einzelbewertung, dann zusammengefasst nach den Bodenfunktionen Lebensraumfunktion, Regelungsfunktion, Informationsfunktion, dem Eigenwert des Bodens (Schutzwürdigkeit) sowie der Empfindlichkeit und Gefährdung (Schutzbedürftigkeit). Im dritten Schritt werden diese Bewertungen dann zu einer gewichteten, verbal-argumentativen Gesamtbewertung der Schutzwürdigkeit und Schutzbedürftigkeit zusammengefasst. Mit Hilfe des Bewertungsverfahrens werden auch Zielkonflikte zwischen den unterschiedlichen Schutzgütern offengelegt. Schutzmaßnahmen ergeben sich dann stringent aus den vorher im Zielsystem gesetzten Prämissen, d.h., Ziele und Maßnahmen sind begründbar gewählt, stehen in einem ökologischen Gesamtzusammenhang und lassen sich sehr gut nachvollziehen. Das hier vorgestellte, neue Bodenschutzkonzept ist für verschiedene Planungsebenen geeignet. Es ist in unterschiedlichen Naturräumen anwendbar, kann verschiedene Schutzziele mit Hilfe des Zielsystems bestimmen und so z.B. die Naturraumvielfalt in einem Gebiet ebenso berücksichtigen wie die Meinungsvielfalt, was unter vorsorgendem Bodenschutz zu verstehen sei.
A complete, well-preserved record of the Cenomanian/Turonian (C/T) Oceanic Anoxic Event 2 (OAE-2) was recovered from Demerara Rise in the southern North Atlantic Ocean (ODP site 1260). Across this interval, we determined changes in the stable carbon isotopic composition of sulfur-bound phytane (δ13Cphytane, a biomarker for photosynthetic algae. The δ13Cphytane record shows a positive excursion at the onset of the OAE-2 interval, with an unusually large amplitude (~7 ‰) compared to existing C/T proto-North Atlantic δ13Cphytane records (3–6 ‰). Overall, the amplitude of the excursion of δ13Cphytane decreases with latitude. Using reconstructed sea surface temperature (SST) gradients for the proto-North Atlantic, we investigated environmental factors influencing the latitudinal δ13Cphytane gradient. The observed gradient is best explained by high productivity at DSDP Site 367 and Tarfaya basin before OAE-2, which changed in overall high productivity throughout the proto-North Atlantic during OAE-2. During OAE-2, productivity at site 1260 and 603B was thus more comparable to the mid-latitude sites. Using these constraints as well as the SST and δ13Cphytane-records from Site 1260, we subsequently reconstructed pCO2 levels across the OAE-2 interval. Accordingly, pCO2 decreased from ca. 1750 to 900 ppm during OAE-2, consistent with enhanced organic matter burial resulting in lowering pCO2. Whereas the onset of OAE-2 coincided with increased pCO2, in line with a volcanic trigger for this event, the observed cooling within OAE-2 probably resulted from CO2 sequestration in black shales outcompeting CO2 input into the atmosphere. Together these results show that the ice-free Cretaceous world was sensitive to changes in pCO2 related to perturbations of the global carbon cycle.
A complete, well-preserved record of the Cenomanian/Turonian (C/T) Oceanic Anoxic Event 2 (OAE-2) was recovered from Demerara Rise in the southern North Atlantic Ocean (ODP site 1260). Across this interval, we determined changes in the stable carbon isotopic composition of sulfur-bound phytane (δ13Cphytane), a biomarker for photosynthetic algae. The δ13Cphytane record shows a positive excursion at the onset of the OAE-2 interval, with an unusually large amplitude (~7‰) compared to existing C/T proto-North Atlantic δ13Cphytane records (3–6‰). Overall, the amplitude of the excursion of δ13Cphytane decreases with latitude. Using reconstructed sea surface temperature (SST) gradients for the proto-North Atlantic, we investigated environmental factors influencing the latitudinal δ13Cphytane gradient. The observed gradient is best explained by high productivity at DSDP Site 367 and Tarfaya basin before OAE-2, which changed in overall high productivity throughout the proto-North Atlantic during OAE-2. During OAE-2, productivity at site 1260 and 603B was thus more comparable to the mid-latitude sites. Using these constraints as well as the SST and δ13Cphytane-records from Site 1260, we subsequently reconstructed pCO2 levels across the OAE-2 interval. Accordingly, pCO2 decreased from ca. 1750 to 900 ppm during OAE-2, consistent with enhanced organic matter burial resulting in lowering pCO2. Whereas the onset of OAE-2 coincided with increased pCO2, in line with a volcanic trigger for this event, the observed cooling within OAE-2 probably resulted from CO2 sequestration in black shales outcompeting CO2 input into the atmosphere. Together these results show that the ice-free Cretaceous world was sensitive to changes in pCO2 related to perturbations of the global carbon cycle.
Subduction zone magmas are more oxidised on eruption than those at mid-ocean ridges. This is attributed either to oxidising components, derived from subducted lithosphere (slab) and added to the mantle wedge, or to oxidation processes occurring during magma ascent via differentiation. Here we provide direct evidence for contributions of oxidising slab agents to melts trapped in the sub-arc mantle. Measurements of sulfur (S) valence state in sub-arc mantle peridotites identify sulfate, both as crystalline anhydrite (CaSO4) and dissolved SO42− in spinel-hosted glass (formerly melt) inclusions. Copper-rich sulfide precipitates in the inclusions and increased Fe3+/∑Fe in spinel record a S6+–Fe2+ redox coupling during melt percolation through the sub-arc mantle. Sulfate-rich glass inclusions exhibit high U/Th, Pb/Ce, Sr/Nd and δ34S (+ 7 to + 11‰), indicating the involvement of dehydration products of serpentinised slab rocks in their parental melt sources. These observations provide a link between liberated slab components and oxidised arc magmas.
Fossil records of early solar irradiation and cosmolocation of the CAI factory: a reappraisal
(2021)
Calcium-aluminum–rich inclusions (CAIs) in meteorites carry crucial information about the environmental conditions of the nascent Solar System prior to planet formation. Based on models of 50V–10Be co-production by in-situ irradiation, CAIs are considered to have formed within ~0.1 AU from the proto-Sun. Here, we present vanadium (V) and strontium (Sr) isotopic co-variations in fine- and coarse-grained CAIs and demonstrate that kinetic isotope effects during partial condensation and evaporation best explain V isotope anomalies previously attributed to solar particle irradiation. We also report initial excesses of 10Be and argue that CV CAIs possess essentially a homogeneous level of 10Be, inherited during their formation. Based on numerical modeling of 50V–10Be co-production by irradiation, we show that CAI formation during protoplanetary disk build-up likely occurred at greater heliocentric distances than previously considered, up to planet-forming regions (~1AU), where solar particle fluxes were sufficiently low to avoid substantial in-situ irradiation of CAIs.
Die vorliegende geologische Arbeit befaßt sich mit einem Ausschnitt des Taunus. Der Taunus ist der südöstlichste Teil des Rheinischen Schiefergebirges und liegt in etwa zwischen Koblenz, Gießen, Frankfurt und Wiesbaden (Abb. 1 und 2). Marine Flachseesedimente prägen hier das Unterdevon des Rheinischen Schiefergebirges. Durch variszische Deformation entstand überwiegend NW- bis NNW-vergenter Faltenbau. Gravitative Kräfte ließen weitere tektonische Strukturen entstehen. Tertiäre Bruchtektonik schuf Horste und Gräben....... Das bearbeitete Gebiet weist unter großflächigen quartären Schuttdecken unterdevonische Sedimente der Tonschiefer- und Feinsandsteinfraktion auf. Im Unterdevon sorgte rasche Sedimentation bei ständiger Absenkung des Rheinischen Trogs für ein flaches Meer. Im Norden des Kartiergebiets tritt eine Fossilbank mit mariner Fauna zutage. Bei der mesozoisch-tertiären Verwitterung wurden die oberflächennahen Gesteine gelockert und Vererzungen und Roterden gebildet. Taleinschnitte in die tertiäre Rumpffläche sind pleistozänen Alters. Das devonische Gestein ist anchimetamorph überprägt und zeigt eine deutliche erste Schieferung, welche von einer intensiven Glimmerneubildung begleitet ist und primär stark nordwestvergent angelegt wurde. In feinpelitischen Bereichen kann eine zweite, postkristalline Schieferung ausgebildet sein. Durch starken Schuppenbau und anhaltende laterale Einengung bei der variszischen Überprägung entstanden im Taunus sogenannte "horse structures": Es kam zu sukzessiver Aufrichtung hangender Schuppeneinheiten bei nordwestlich fortschreitender Anlage von Überschiebungsbahnen im Liegenden. Im Scheitelbereich eines so entstandenen Vergenzfächers liegt das Kartiergebiet. Achsenflächen und Hauptschieferung stehen steil bis saiger. In diesen Bereichen kam es beim Kollaps des Gebirges durch gravitative Kräfte zur Anlage von Knickbändern. Sie ersetzen Verschiebungsflächen. Vereinzelt sind sie auch mit Abschiebungen verbunden. Die am häufigsten aufgeschlossene Knickband-Schar hat nach SE abschiebenden Charakter, eine zweite zeigt NW-gerichteten Bewegungssinn. Sie sind aufgrund der gleichgerichteten vertikalen Einengung zusammengehörend bzw. konjungiert. Die Knickachsen beider Scharen tauchen mit nur wenigen Grad in Streichrichtung ab. Manchmal sind Knickbänder dieser beiden Gruppen direkt konjungiert aufgeschlossen. Möglicherweise durch Rotation, als Teil konjungierter Knickbänder oder innerhalb größerer übergeordneter Knickbänder erscheinen einige der Knickbänder aufschiebend. Eine untergeordnete, dritte Knickband-Schar deutet mit schrägabschiebendem Verschiebungssinn eine Rotation der Spannungsrichtung und möglicherweise erste Bewegungen der Idsteiner Senke an. Sie ist im Untersuchungsgebiet nur selten aufgeschlossen. Die Untersuchungen im Zuge dieser Diplomarbeit ergaben, daß die Knickbänder bevorzugt in Bereichen südvergenter Schieferung entstanden. Im Süden und südlich des Kartiergebiets weist die Schieferung häufiger Südvergenz auf, weshalb dort fast ausschließlich nach S bis SE abschiebende Knickbänder einzumessen waren. Unterschiede zwischen Messungen im Westen und Osten des Gebiets wurden nicht festgestellt. Ein weiteres Ergebnis dieser Arbeit ist eine Longitudinalstrain-Berechnung von 3,4-6,8 % für die Gesteinspartien mit Knickbändern. Die Anlage der Knickbänder wird als letzte variszische Deformation angesehen. Ihr folgten außer kleineren Abschiebungen möglicherweise noch syn- und antithetische Rotationsbewegungen einzelner Gesteinsschollen. Demnach würden sich insgesamt die Anlage der Knickbänder und die Bildung der Vergenzfächer zeitlich überschneiden. Das Einfallen der Knickachsen und auch anderer Achsen und Lineare flach nach SW, ist wahrscheinlich durch tertiäre Bruchschollentektonik bedingt. Diese Bruchtektonik gliedert das Gebirge in Schollen mit Horsten und Gräben, so z.B. die bedeutende Grabenstruktur der Idsteiner Senke. Dabei kann der Vergenzfächer trotz vertikaler Bewegung horizontal versetzt worden sein. Seine Scheitellinie verändert zur Tiefe hin die Position ("horse structures") und tritt bei einer erodierten Hochscholle versetzt zutage.
Aus mehreren Datenquellen wurde ein neuer globaler Niederschlagsdatensatz für die Zeit 1951-2000 generiert, der unter der Bedingung einer Mindestverfügbarkeit von 90 % genau 9.343 Stationen umfasst. Die betreffenden Zeitreihen wurden einer umfassenden Qualitätskontrolle unterzogen, was zu äußerst zahlreichen Korrekturen führte, einschließlich Tests auf Ausreißer und Homogenität sowie Homogenisierung. Daraus entstand ein Gitterpunktdatensatz in 0,5° x 0,5°- Auflösung, was für die Landgebiete (ausgenommen Grönland und Antarktis) rund 71.000 Gitterpunkte ergibt, und über INTERNET frei verfügbar bereitgestellt. Davon ausgehend und unter Nutzung weiterer vorliegender Datensätze, insbesondere der Temperatur, wurden zunächst einige grundlegende Untersuchungen zur globalen und regionalen Klima- und Niederschlagsvariabilität durchgeführt. Diese Arbeiten umfassten Analysen der Veränderungen des global gemittelten Niederschlages und potentieller Einflussgrößen, die Neuberechnung der globalen Klimaklassifikation nach Köppen, Untersuchungen zur raumzeitlichen Struktur von Niederschlagsänderungen global sowie speziell in Afrika und schließlich Analysen der raumzeitlichen Beziehungen zwischen großräumiger atmosphärischer Zirkulation und Niederschlag im nordatlantisch-europäischen Bereich. Für weitergehende statistische Analysen wurde eine neue Methode der vollständigen Zeitreihenmodellierung entwickelt, um die die in diesen Reihen enthaltenen signifikanten Variationskomponenten durch Regressionstechniken zu erfassen und in ihrem raumzeitlichen Verhalten darzustellen. Dabei lag ein Schwerpunkt dieser Arbeiten auf der Extremwertanalyse, die es nun gestattet, unabhängig vom Verteilungstyp für beliebige Schwellenwerte den zeitlichen Verlauf der Unter- sowie Überschreitungswahrscheinlichkeit anzugeben und somit zu erkennen, inwieweit das Klima extremer geworden ist. Dabei zeigte sich je nach Region die Gumbel- oder die Weibull-Verteilung als geeignet. Regionale Schwerpunkte waren dabei u.a. Deutschland bzw. Europa, auch hinsichtlich der Erstellung neuer Klimatrendkarten nach der üblichen linearen Methode (der kleinsten Quadrate) sowie der innovativen. Weiterhin wurden nach der innovativen Methode Klimamodelldaten des Hamburger Max-Planck-Instituts für Meteorologie (IPCC Szenario A2) hinsichtlich des Niederschlag-Extremverhaltens in Europa untersucht. Schließlich erfolgte eine Abschätzung der Wiederkehrzeiten täglicher Extremniederschläge in Deutschland und deren Unsicherheit.
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.
An update of the two-energy turbulence scheme is presented, the 2TE + APDF scheme. The original version of the two-energy scheme is able to successfully model shallow convection without the need of an additional parameterization for non-local fluxes. However, the performance of the two-energy scheme is worse in stratocumulus cases, where it tends to overestimate the erosion of the stable layers. We have identified the causes: the non-local stability parameter does not consider local stratification, the scheme lacks an internal parameter that could distinguish between a shallow convection regime and a stratocumulus regime, and it uses an inflexible turbulence length scale formulation. To alleviate this problem, we propose several modifications: an update of the stability parameter, a modified computation of the turbulence length scale, and the introduction of the entropy potential temperature to distinguish between a shallow convection and a stratocumulus regime. In addition, the two-energy scheme is coupled to a simplified assumed probability density function method in order to achieve a more universal representation of the cloudy regimes. The updated turbulence scheme is evaluated for several idealized cases and one selected real case in the ICOsahedral Nonhydrostatic (ICON) modeling framework. The results show that the updated scheme corrects the overmixing problem in the stratocumulus cases. The performance of the updated scheme is comparable to the operational setup, and can be thus used instead of the operational turbulence and shallow convection scheme in ICON. Additionally, the updated scheme improves the coupling with dynamics, which is beneficial for the modeling of coherent flow structures in the atmospheric boundary layer.
The ICON single-column mode
(2021)
The single-column mode (SCM) of the ICON (ICOsahedral Nonhydrostatic) modeling framework is presented. The primary purpose of the ICON SCM is to use it as a tool for research, model evaluation and development. Thanks to the simplified geometry of the ICON SCM, various aspects of the ICON model, in particular the model physics, can be studied in a well-controlled environment. Additionally, the ICON SCM has a reduced computational cost and a low data storage demand. The ICON SCM can be utilized for idealized cases—several well-established cases are already included—or for semi-realistic cases based on analyses or model forecasts. As the case setup is defined by a single NetCDF file, new cases can be prepared easily by the modification of this file. We demonstrate the usage of the ICON SCM for different idealized cases such as shallow convection, stratocumulus clouds, and radiative transfer. Additionally, the ICON SCM is tested for a semi-realistic case together with an equivalent three-dimensional setup and the large eddy simulation mode of ICON. Such consistent comparisons across the hierarchy of ICON configurations are very helpful for model development. The ICON SCM will be implemented into the operational ICON model and will serve as an additional tool for advancing the development of the ICON model.
This article reviews the most recent results concerning second harmonic generation (SHG) experiments of non-phase matchable and phase matchable powder samples at high pressures and explains the pressure dependence of the intensity of the SHG signal by correlating it to the ratio between the average coherence length and the average particle size. The examples discussed here include pressure-induced structural changes in quartz, ZnO, ice VII and KIO3. It is shown that the second harmonic generation technique is a unique tool for the detection of pressure-induced structural phase transitions. It is laboratory based and allows fast measurements. It is complementary to X-ray diffraction and provides additional information about the presence of an inversion center for unknown or controversially discussed structures at high pressure.
The forest, savanna, and grassland biomes, and the transitions between them, are expected to undergo major changes in the future due to global climate change. Dynamic global vegetation models (DGVMs) are very useful for understanding vegetation dynamics under the present climate, and for predicting its changes under future conditions. However, several DGVMs display high uncertainty in predicting vegetation in tropical areas. Here we perform a comparative analysis of three different DGVMs (JSBACH, LPJ-GUESS-SPITFIRE and aDGVM) with regard to their representation of the ecological mechanisms and feedbacks that determine the forest, savanna, and grassland biomes, in an attempt to bridge the knowledge gap between ecology and global modeling. The outcomes of the models, which include different mechanisms, are compared to observed tree cover along a mean annual precipitation gradient in Africa. By drawing on the large number of recent studies that have delivered new insights into the ecology of tropical ecosystems in general, and of savannas in particular, we identify two main mechanisms that need improved representation in the examined DGVMs. The first mechanism includes water limitation to tree growth, and tree–grass competition for water, which are key factors in determining savanna presence in arid and semi-arid areas. The second is a grass–fire feedback, which maintains both forest and savanna presence in mesic areas. Grasses constitute the majority of the fuel load, and at the same time benefit from the openness of the landscape after fires, since they recover faster than trees. Additionally, these two mechanisms are better represented when the models also include tree life stages (adults and seedlings), and distinguish between fire-prone and shade-tolerant forest trees, and fire-resistant and shade-intolerant savanna trees. Including these basic elements could improve the predictive ability of the DGVMs, not only under current climate conditions but also and especially under future scenarios.
The forest, savanna, and grassland biomes, and the transitions between them, are expected to undergo major changes in the future, due to global climate change. Dynamic Global Vegetation Models (DGVMs) are very useful to understand vegetation dynamics under present climate, and to predict its changes under future conditions. However, several DGVMs display high uncertainty in predicting vegetation in tropical areas. Here we perform a comparative analysis of three different DGVMs (JSBACH, LPJ-GUESS-SPITFIRE and aDGVM) with regard to their representation of the ecological mechanisms and feedbacks that determine the forest, savanna and grassland biomes, in an attempt to bridge the knowledge gap between ecology and global modelling. Model outcomes, obtained including different mechanisms, are compared to observed tree cover along a mean annual precipitation gradient in Africa. Through these comparisons, and by drawing on the large number of recent studies that have delivered new insights into the ecology of tropical ecosystems in general, and of savannas in particular, we identify two main mechanisms that need an improved representation in the DGVMs. The first mechanism includes water limitation to tree growth, and tree-grass competition for water, which are key factors in determining savanna presence in arid and semi-arid areas. The second is a grass-fire feedback, which maintains both forest and savanna occurrences in mesic areas. Grasses constitute the majority of the fuel load, and at the same time benefit from the openness of the landscape after fires, since they recover faster than trees. Additionally, these two mechanisms are better represented when the models also include tree life stages (adults and seedlings), and distinguish between fire-prone and shade-tolerant savanna trees, and fire-resistant and shade-intolerant forest trees. Including these basic elements could improve the predictive ability of the DGVMs, not only under current climate conditions but also and especially under future scenarios.
This research was conducted in the Rwenzori Region of the Western Branch, East African Rift System (EARS). The EARS is a tectonic structure extending over a length of more than 3000 km from the Afar Triple Junction, in Ethiopia, to Lake Malawi in the south. The Western Rift System is a roughly NE to ENE trending sector of the EARS, which runs along the western boundary of Uganda and the neighboring Democratic Republic of Congo (D.R.C). It stretches 2100 km from Nimule, NW on Uganda-Sudan border, extending to Lake Malawi in the SE of Africa. The unusual uplift of the Rwenzori Mountains within an extensional regime and the mechanisms associated with the high frequency of seismic activity in the region was hardly understood and therefore, had remained a subject of contention that needed to be critically addressed in detail. To my knowledge, this was probably the first study to be performed and documented in great depth within the domains of seismic noise variation, seismic anisotropy and b value analyses beneath the Rwenzori Region. After about six years of operation (2006-2012), the seismology group of the RIFTLINK Research Project (www.riftlink.org) acquired a vast amount of high-quality, digital data that were collected using a seismic network of well calibrated seismic equipment. The project was divided into two phases. Phase I, that operated between February 2006 - September 2007, consisted of thirty-two temporary seismic stations, which were selectively spread out in the Rwenzori Region on the Ugandan side, to detect and record extremely weak as well as strong naturally occurring earthquakes. The seismic equipment used included EDL and REFTEK digitizers, which were coupled with Güralp and MARK sensors respectively (REFTEKS: only short-period MARK sensors, EDLs: short-period MARK plus few broadband Güralp Sensors). Exactly 22375 earthquakes were recorded. The data were processed using the SEISAN software package. About 14413 earthquakes were carefully localized using the velocity model of Bram (1975) that implements a Vp=Vs ratio fixed at 1.74. Phase II, that extended between 2009-2012 consisted of thirty-two seismic stations, which were spread out around the Rwenzori Mountains, both on the Ugandan side and the neighboring D.R.C. Only Taurus digitizers that were coupled with Trillium sensors were used in the D.R.C. On the Ugandan side however, both EDL and Taurus digitizers, which were coupled with Trillium and Güralp sensors were used. ...
During the Late Cretaceous and early Cenozoic the Earth experienced prolonged climatic cooling most likely caused by decreasing volcanic activity and atmospheric CO2 levels. However, the causes and mechanisms of subsequent major global warming culminating in the late Paleocene to Eocene greenhouse climate remain enigmatic. We present deep and intermediate water Nd-isotope records from the North and South Atlantic to decipher the control of the opening Atlantic Ocean on ocean circulation and its linkages to the evolution of global climate. The marked convergence of Nd-isotope signatures 59 million years ago indicates a major intensification of deep-water exchange between the North and South Atlantic, which coincided with the turning point of deep-water temperatures towards early Paleogene warming. We propose that this intensification of Atlantic overturning circulation in concert with increased atmospheric CO2 from continental rifting marked a climatic tipping point contributing to a more efficient distribution of heat over the planet.
The oceans at the time of the Cenomanian–Turonian transition were abruptly perturbed by a period of bottom-water anoxia. This led to the brief but widespread deposition of black organic-rich shales, such as the Livello Bonarelli in the Umbria–Marche Basin (Italy). Despite intensive studies, the origin and exact timing of this event are still debated. In this study, we assess leading hypotheses about the inception of oceanic anoxia in the Late Cretaceous greenhouse world by providing a 6 Myr long astronomically tuned timescale across the Cenomanian–Turonian boundary. We procure insights into the relationship between orbital forcing and the Late Cretaceous carbon cycle by deciphering the imprint of astronomical cycles on lithologic, physical properties, and stable isotope records, obtained from the Bottaccione, Contessa and Furlo sections in the Umbria–Marche Basin. The deposition of black shales and cherts, as well as the onset of oceanic anoxia, is related to maxima in the 405 kyr cycle of eccentricity-modulated precession. Correlation to radioisotopic ages from the Western Interior (USA) provides unprecedented age control for the studied Italian successions. The most likely tuned age for the base of the Livello Bonarelli is 94.17 ± 0.15 Ma (tuning 1); however, a 405 kyr older age cannot be excluded (tuning 2) due to uncertainties in stratigraphic correlation, radioisotopic dating, and orbital configuration. Our cyclostratigraphic framework suggests that the exact timing of major carbon cycle perturbations during the Cretaceous may be linked to increased variability in seasonality (i.e. a 405 kyr eccentricity maximum) after the prolonged avoidance of seasonal extremes (i.e. a 2.4 Myr eccentricity minimum). Volcanism is probably the ultimate driver of oceanic anoxia, but orbital periodicities determine the exact timing of carbon cycle perturbations in the Late Cretaceous. This unites two leading hypotheses about the inception of oceanic anoxia in the Late Cretaceous greenhouse world.
The organic rich Livello Bonarelli formed as a result of oxygen deficiency and carbonate dissolution in the oceans during the Cenomanian/Turonian (C/T) transition. During this Ocean Anoxic Event 2 (OAE2), a combination of factors caused increased productivity, incomplete decomposition of organic matter and widespread deposition of black shales. Although these sediments are extensively studied, the exact extent, cause, timing and duration of oceanic anoxia are debated (Sinton and Duncan, 1997; Mitchell et al., 2008). Contrasting causal mechanisms have been suggested, including stratification of the water column (Lanci et al., 2010) versus intensification of the hydrological cycle driving a dynamic ocean circulation (Trabucho-Alexandre et al., 2010). Studies on trace-elemental and (radiogenic) isotope compositions of Cenomanian marine successions have suggested a volcanic origin of OAE2, by delivering nutrients to the semi-enclosed proto-North Atlantic (Zheng et al., 2013, and references therein; Du Vivier et al., 2014). Deciphering the importance of volcanic and oceanographic processes requires tight constraints on their relative timing. Regularly occurring black cherts and shales below the Livello Bonarelli demonstrate that oceanic conditions in the Umbria-Marche Basin were punctuated by episodes of regional anoxia from the mid-Cenomanian onwards. Their hierarchical stacking pattern suggests an orbital control on the deposition of organic rich horizons (Mitchell et al., 2008; Lanci et al., 2010). Stable carbon isotope data reveal that long-term 15 variations in eccentricity paced the carbon cycle (Sprovieri et al., 2013) and sea level changes (Voigt et al., 2006) of the Late Cretaceous. Here we investigate the role of orbital forcing on climate and the carbon cycle, and, specifically, on organic-rich sedimentation prior, during, and after OAE2.
We also explore the potential for establishing an anchored astrochronology for the C/T interval in Europe. Recent improvements in the astronomical solution (La2011; Laskar et al., 2011b) and in the intercalibration of radiometric and astronomical dating techniques (Kuiper et al., 2008; Renne et al., 2013) allow the extension of the astronomical time scale into the Cretaceous. The C/T boundary in the Western Interior (USA) has been dated at 93.90 ± 0.15 Ma by intercalibration of radio-isotopic and astrochronologic time scales (Meyers et al., 2012b). Also, reinterpretation of proxy records spanning the C/T interval seems to resolve discrepancies in reported durations of the OAE2 (Sageman et al., 2006; Meyers et al., 2012a). The well-documented Italian rhythmic successions, reference sections for climatic processes in the Tethyan realm, need to be tied in with the absolute time scale. Biostratigraphic correlation to radioisotopically-dated ash beds in the Western Interior is complicated by the provinciality of faunas and floras. However, δ13C stratigraphy provides a reliable correlation tool (Gale et al., 2005) and we present a new 40Ar/39Ar age for the Thatcher bentonite from the Western Interior occurring within the mid-Cenomanian δ13C event (MCE). This study integrates the well-developed cyclostratigraphy from the Umbria-Marche Basin with radioisotopic ages from the Western Interior and derives a numerical timescale for this critical interval in Earth’s history.
Buchbesprechungen
(1996)
Besprochen werden die beiden folgenden Werke:
(1) Handbuch der Bodenkunde - Grundwerk. Von H. P. Blume , P. Felix-Henningsen, W.R. Fischer, H.-G. Frede, R. Horn u. K. Stahr.
(2) Thienemann, Johannes: Rossitten - drei Jahrzehnte auf der Kurischen Nehrung. Reprint der Ausgabe Melsungen, Neumann-Neudamm von 1930 (3.Aufl.).
Clastic deposits related to alluvial and estuarine environments sedimented during the early Liassic in the Veillon area (south of Talmont-Saint-Hilaire, Vendée, France). A reptile fauna including various taxa, just known by innumerable footprints, lived in that environment, in rather hot and dry climatic conditions.
Tetra-auricupride, ideally AuCu, represents the only species showing the coexistence of Au with an elevated level of Pt, as in the case of a detrital grain studied structurally for the first time, from an ophiolite-associated placer at Bolshoy Khailyk, western Sayans, Russia. We infer that tetra-auricupride can incorporate as much as ~30 mol. % of a “PtCu” component, apparently without significant modification of the unit cell. The unit-cell parameters of platiniferous tetra-auricupride are: a 2.790(1) Å, c 3.641(4) Å, with c/a = 1.305, which are close to those reported for ordered AuCu(I) in the system Au–Cu, and close also to the cell parameters of tetraferroplatinum (PtFe), which both appear to crystallize in the same space group, P4/mmm. These intermetallic compounds and natural alloys are thus isostructural. The closeness of their structures presumably allows Pt to replace Au atoms so readily. The high extent of Cu + Au enrichment is considered to be a reflection of geochemical evolution and buildup in levels of the incompatible Cu and Au with subordinate Pt in a remaining volume of melt at low levels of fO2 and fS2 in the system.
Si espongono i risultati delle ricerche, riguardo agli scavi alla stratigrafia, la sedimentologia e alla industria litica, nel giacimento di Montemiletto (AV). Si tratta di una frattura beante il cui riempimento è probabilmente avvenuto in un breve arco di tempo e comprende tre momenti principali di sedimentazione: sedimenti fini (argille) nella parte più bassa, grossolani (sabbie) nella parte mediana e ancora fini (limi) in quella alta. L'industria litica, raccolta in tutti i livelli, e omogenea nell'intera serie, è riferita ad un Musteriano a denticolati, caratterizzato da una scarsa varietà di tipi; in genere su scheggia piatta; di tecnica debolmente levallois.
Evidence of hydrothermal activity is reported for the Mesozoic pre- and syn-rift successions of the western Adriatic palaeomargin of the Alpine Tethys, preserved in the Western Southalpine Domain (NW Italy). The products of hydrothermal processes are represented by vein and breccia cements, as well as dolomitization and silicification of the host rocks. In the eastern part of the study area, interpreted as part of the necking zone of the continental margin, Middle Triassic dolostones and Lower Jurassic sediments are crossed by veins and hydrofracturing breccias cemented by saddle dolomite. The precipitation of dolomite cements occurred within the stratigraphic succession close to the sediment–water interface. Despite the shallow burial depth, fluid inclusion microthermometry and clumped isotopes show that hydrothermal fluids were relatively hot (80–150°C). In the western part of the study area, interpreted as part of the hyperextended distal zone, a polyphase history of host-rock fracturing is recorded, with at least two generations of veins cemented by calcite, dolomite and quartz. Vein opening and cementation occurred at shallow burial depth around the time of deposition of the syn-rift clastic succession. Fluid inclusion microthermometry on both quartz and dolomite cements indicates a fluid temperature of 90–130°C, again pointing to hydrothermal fluids. Both in Fenera-Sostegno and Montalto Dora areas, O, C and Sr isotope values, coupled with fluid inclusion and clumped isotope data, indicate that hydrothermal fluids derived from seawater interacted with crustal rocks during hydrothermal circulation. Stratigraphic and petrographic evidence, and U–Pb dating of dolomitized clasts within syn-rift sediments, document that hydrothermal fluids circulated through sediments from the latest Triassic to the Toarcian, corresponding to the entire syn-rift evolution of the western portion of the Adriatic palaeomargin. The documented hydrothermal processes are temporally correlated with regional-scale thermal events that took place in the same time interval at deeper crustal levels.
Surface temperature is a fundamental parameter of Earth’s climate. Its evolution through time is commonly reconstructed using the oxygen isotope and the clumped isotope compositions of carbonate archives. However, reaction kinetics involved in the precipitation of carbonates can introduce inaccuracies in the derived temperatures. Here, we show that dual clumped isotope analyses, i.e., simultaneous ∆47 and ∆48 measurements on the single carbonate phase, can identify the origin and quantify the extent of these kinetic biases. Our results verify theoretical predictions and evidence that the isotopic disequilibrium commonly observed in speleothems and scleractinian coral skeletons is inherited from the dissolved inorganic carbon pool of their parent solutions. Further, we show that dual clumped isotope thermometry can achieve reliable palaeotemperature reconstructions, devoid of kinetic bias. Analysis of a belemnite rostrum implies that it precipitated near isotopic equilibrium and confirms the warmer-than-present temperatures during the Early Cretaceous at southern high latitudes.
Brachiopod shells are the most widely used geological archive for the reconstruction of the temperature and the oxygen isotope composition of Phanerozoic seawater. However, it is not conclusive whether brachiopods precipitate their shells in thermodynamic equilibrium. In this study, we investigated the potential impact of kinetic controls on the isotope composition of modern brachiopods by measuring the oxygen and clumped isotope compositions of their shells. Our results show that clumped and oxygen isotope compositions depart from thermodynamic equilibrium due to growth rate-induced kinetic effects. These departures are in line with incomplete hydration and hydroxylation of dissolved CO2. These findings imply that the determination of taxon-specific growth rates alongside clumped and bulk oxygen isotope analyses is essential to ensure accurate estimates of past ocean temperatures and seawater oxygen isotope compositions from brachiopods.
Abstract: Subaqueous carbonates from the Devils Hole caves (southwestern USA) provide a continuous Holocene to Pleistocene North American paleoclimate record. The accuracy of this record relies on two assumptions: That carbonates precipitated close to isotope equilibrium and that groundwater temperature did not change significantly in the last 570 thousand years. Here, we investigate these assumptions using dual clumped isotope thermometry. This method relies on simultaneous analyses of carbonate ∆47 and ∆48 values and provides information on the existence and extent of kinetic isotope fractionation. Our results confirm the hypothesis that calcite precipitation occurred close to oxygen and clumped isotope equilibrium during the last half million years in Devils Hole. In addition, we provide evidence that aquifer temperatures varied by less than ±1°C during this interval. Thus, the Devils Hole calcite δ18O time series exclusively represents changes in groundwater δ18O values. Plain Language Summary: The oxygen isotope composition of cave carbonates records changes in Earth's climate. However, the reliability of such records depends on how stable the carbonate precipitation environment was. Here, we use a novel method called dual clumped isotope thermometry that can provide simultaneous information on a carbonate's growth temperature and whether any additional fractionation processes affected its oxygen and clumped isotope signatures. Specifically, we investigated the Devils Hole caves, which provide a reference oxygen isotope time series for North America. We find that groundwater temperature did not change significantly in the last half-million years. Variations in the oxygen isotope composition of the deposited carbonates solely reflect variations in the oxygen isotope composition of the groundwater.
During my PhD, I was applying the clumped isotope technique to modern brachiopods and fossil belemnites, and I conducted methodological work. Carbonate clumped isotope thermometry is a tool to reconstruct carbonate precipitation temperatures. In contrast to oxygen isotope thermometry, i.e., the δ18O-thermometer, the carbonate clumped isotope thermometer does not require an estimate for the oxygen isotope composition of the seawater, as it considers the fractionation of isotopes exclusively amongst carbonate isotopologues. The ∆47 value of a carbonate expresses the abundance of the 13C–18O bond bearing carbonate isotopologue, within the carbonate, relative to its random distribution. In thermodynamic equilibrium, the ∆47 value of a given carbonate is solely a function of the carbonate precipitation temperature. However, kinetic isotope fractionations, i.e., vital effects, driven by diffusion, pH or incomplete oxygen isotope exchange between water and dissolved inorganic carbonate species can cause the carbonate to be precipitated with isotopic compositions that are offset from those predicted for thermodynamic equilibrium.
Brachiopods serve as important geochemical archives of past climate conditions. To investigate the nature and significance of kinetic controls on brachiopod shell δ18O and ∆47 values, in collaboration with the BASE-LiNE Earth ITN, I analysed the bulk and clumped isotope compositions of eighteen modern brachiopod shells, collected from different geographic locations and water depths that cover a substantial range of growth temperatures. Growth temperatures and seawater δ18O values for each brachiopod were independently determined. Most of the analysed brachiopods exhibit combined offsets from clumped and oxygen isotope equilibrium, and there is a significant negative correlation between the offset values. The observed correlation slope between offset ∆47 and offset δ18O point to the importance of kinetic effects associated with Knudsen diffusion and incomplete hydration and hydroxylation of CO2 (aq), occurring during biomineralisation. The correlations between the growth rates of the analysed brachiopods and both the offset ∆47 and the offset δ18O values provide further arguments for the presence of kinetic effects. In conclusion, the oxygen and clumped isotope composition of modern brachiopod shells are affected by growth rate-induced kinetic effects that hinder their use for palaeoceanography.
Schwermetall-Untersuchungen entlang der Düte und der Hase zeigen die starke Belastung der Auenböden jeweils unterhalb der Städte Georgsmarienhütte bzw. Osnabrück. In den Böden beider Auen erreichen Blei, Zink und Cadmium beträchtliche, die Bodenwerte der AbfKlärVO (1992) z.T. erheblich überschreitende Werte. In den Böden entlang der Hase tritt zudem Kupfer mit besonders hohen Werten auf. Diese Unterschiede stehen in Zusammenhang mit der Art der jeweiligen Industriestandorte (Eisenhütte bzw. Metaliverarbeitung).
Als abschließende Glieder regressiver Sedimentationsphasen treten im westlichen Wiehengebirge innerhalb oberjurassischer Sand-, Mergel- und Tonstein-Wechselfolgen "Bröckeltonsteine" auf, die sich durch große Mächtigkeit (bis über 10 m), homogene schluffig-tonige Textur, auffallend grobpolyedrische Struktur, glänzende, mit etwa 20°–40° Grad geneigte Gleitflächen ("Slickensides") und domartige, einander randlich durchschneidende Aufwölbungs-Strukturen von 1,5 - 3 m horizontaler Ausdehnung auszeichnen. Die in semiariden bis subhumiden Überflutungs- Landschaften gebildeten Sedimente wurden synsedimentär durch Peloturbation beeinflusst. Dies erklärt die teilweise extrem große Mächtigkeit der vertischen Merkmale. Mikromorphologisch zeigt das Material deutlich ausgeprägte Bioturbations-Merkmale sowie Stress-Kutane. Erhöhte Temperaturen durch die Aktivität eines Plutons in der Kreide-Zeit scheinen eine Smektit-zu-Illit-Umwandlung und eine diagenetische Kornvergrößerung bewirkt zu haben. Im Verlauf der synsedimentären Bodenbildung kam es zu einer deutlichen Kompaktierung, sodass Groß-Dinosaurier über die Flächen hinweg schreiten konnten, ohne tiefer als etwa 5 cm einzusinken. Im Quartär dürfte es zu teilweise intensiver Eisen-Umverteilung, zum Eindringen von Ton in Spalten sowie zur Freilegung der bereits im Jura präformierten Polyeder ("Bröckel") gekommen sein.
The Alborz Mountains are forming a ~100 km wide, E-W trending mountain chain where individual summits are up to 5000 m in elevation. The Alborz Mountains range are part of the Alpine orogen and are straddling a 2000 km wide area S of the Caspian Sea. The rocks of the Alborz Mountains consist of Neogen sediments, which are affected by folding and faulting. In the western part of the Alborz Mountains the folds and faults are trending NW-SE, whereas in the eastern part they are trending NE-SW. GPS data confirm N-S shortening including dextral strike-slip along ESE-WNW trending faults, and sinistral strike-slip along ENE-WSW trending faults. The present thesis is focusing on the active Garmsar salt nappe, the fragmented roof of which is pierced by rock salt which extruded near the front of the Alborz Mountains Range. During the past 5 m.y. the front of the Alborz chain migrated towards SSW on top of the salt of the Garmsar basin. The salt was squeezed towards SSW and took place at the Great Kavir. The extruded salt is forming the Eyvanekey plateau between the cities of Eyvanekey and Garmsar. Both the Garmsar salt nappe and the Eyvanekey plateau are dextrally displaced for ca. 9 km along the Zirab-Garmsar fault. Structural analyses of the Garmsar salt nappe indicate three different groups of joints which are trending perpendicular and parallel to the local mechanical anisotropy. The folds of the study area are congruent (type 2 and 3 after Ramsay) resulting from viscose inhomogeneous flow. InSAR-Investigations suggest the Alborz Mountains to be lifted up by ca. 1 cm/a, while horizontal shortening is active at a rate of 8 ±2 mm/a. These values are consistent with GPS data. Based on nine „Advanced Synthetic Aperture Radar“ (ASAR) scenarios, produced by the ENVISAT satellite of the European space agency between 2003 and 2006, we used interferograms to map the displacement via 22 increments during 2 – 18 months. The results suggest that the topographic height of the surface of the salt is changing at a rate which is controlled by the season. The displacement ranges from subsidence at -40 to -50 mm/a to uplift of 20 mm/a. In order to investigate the time-dependent deformation with high spatial resolution, we used algorithms which are based on data of small base lines (SBAS). The resulting interferometric SAR time series analyses also suggest that the study area is largely subsiding at a rate that is controlled by the seasons. The map with the averaged LOS deformation velocities, on the other hand, suggests the subsidence to increase from the upper part of the salt nappe towards deeper topographic 5 levels of the agricultural lowlands. The major part of subsidence is probably caused by the annual rainfall which results in subrosion of salt. The spatial changes in the subsidence rate are probably controlled by the distribution of fountains, mining activity at the margin of the salt glacier, and faults and fractures inside the salt. Striking seasonal imprints are obvious along the agricultural areas which are surrounding the Garmsar salt nappe. These areas are rapidly subsiding in summer and spring when groundwater is used for irrigations. The maximum rate of subsidence (40-50 mm/a) is located E and W of the Eyvanekey plateau, where large areas are irrigated. The maximum displacement is 20 mm/a in the farmland and 5 mm/a in the center of the salt nappe. Depth estimates using Euler deconvolution method for gravimetric and magnetic data suggest the salt to extrude from a depth less than ca. 2000 m. The gravity field of the study area is characterized by strong anomalies in the SW and weak anomalies in the NE. A considerable negative anomaly in the N indicates that the northern part subsided, whereas the southern part was lifted up. The seismic data show three major horizons inside the Miocene sediments: the Lower Red Formation, the Qom Formation, and the Upper Red Formation. The western part of the study area seems to be free from salt domes. The layers of the upper part of the Qom Formation show thinning along the NE and NW trending faults. In some areas the seismic reflectors indicate steep faults close the saddle of the folds. NE-SW-, NW-SE and E-Wtrending faults prevail. Analogue experiments have been carried out to extend our knowledge about the evolution of the Garmsar salt dome. We used a scaled model (34 cm * 25 cm * 2.5 cm) that was shortened perpendicular to its long side. The wedge shape of the Alborz Mountains was simulated by a wedge consisting of Styrofoam. Rock salt was simulated using Polydimethylsiloxan (PDMS), a linear viscous material with a viscosity of 2.3*104 Pa s and a density of 0.96 g/cm3 at room temperature. Other sediments were modeled using dry quartz sand. The experimental results can be used to simulate the structural evolution of the study area: The Alborz deformation front was emplaced on top of the salt rocks in the Garmsar area while migrating towards SSW. A salt basin and a salt extrusion have also been produced in the model. Cross sections through the wedge shaped analogue model indicate N- and S-dipping reverse faults, which are in line with the wedge shape of the Alborz chain. Moreover, ENE-WSW trending sinistral and ESE-WNW trending dextral strike-slip faults led to N-S shortening during the Miocene. Structural marker horizons, 6 which have been turned into Z-folds on the western fold limbs and to S-folds on the eastern fold limbs, are comparable with the folds of the study area. Solving the problem of waste is one of the central tasks of environmental protection. It is becoming increasingly difficult to find suitable sites that are acceptable to the public. Salt and salt formations have relevant properties to be utilizing as a repository for each kind of waste. The favorable properties make rock salt highly suitable as a host rock, in particular for nonradioactive and radioactive wastes. The Qom and Garmsar basins are the nearest salt diapirs to the Tehran province, and there are suitable repositories for waste disposal. Based on surface and subsurface data, the Garmsar salt diapir has been investigated as a case example for its suitability as a host and repository for various types of waste. The data used are based on field studies, interferometry, and geophysical investigations. The results of this study suggest the deep bedded salt of the Garmsar Salt Basin to be an appropriate host for the deposition of industrial waste. Rock salt of surficial layers or domes, on the other hand, is not regarded as an appropriate candidate for waste disposal.
Chemical reduction-oxidation mechanisms within mantle rocks link to the terrestrial carbon cycle by influencing the depth at which magmas can form, their composition, and ultimately the chemistry of gases released into the atmosphere. The oxidation state of the uppermost mantle has been widely accepted to be unchanged over the past 3800 m.y., based on the abundance of redox-sensitive elements in greenstone belt–associated samples of different ages. However, the redox signal in those rocks may have been obscured by their complex origins and emplacement on continental margins. In contrast, the source and processes occurring during decompression melting at spreading ridges are relatively well constrained. We retrieve primary redox conditions from metamorphosed mid-oceanic ridge basalts (MORBs) and picrites of various ages (ca. 3000–550 Ma), using V/Sc as a broad redox proxy. Average V/Sc values for Proterozoic suites (7.0 ± 1.4, 2σ, n = 6) are similar to those of modern MORB (6.8 ± 1.6), whereas Archean suites have lower V/Sc (5.2 ± 0.4, n = 5). The lower Archean V/Sc is interpreted to reflect both deeper melt extraction from the uppermost mantle, which becomes more reduced with depth, and an intrinsically lower redox state. The pressure-corrected oxygen fugacity (expressed relative to the fayalite-magnetite-quartz buffer, ΔFMQ, at 1 GPa) of Archean sample suites (ΔFMQ –1.19 ± 0.33, 2σ) is significantly lower than that of post-Archean sample suites, including MORB (ΔFMQ –0.26 ± 0.44). Our results imply that the reducing Archean atmosphere was in equilibrium with Earth’s mantle, and further suggest that magmatic gases crossed the threshold that allowed a build-up in atmospheric O2 levels ca. 3000 Ma, accompanied by the first “whiffs” of oxygen in sediments of that age.
Cratonic eclogite is the product of oceanic crust subduction into the subcontinental lithospheric mantle, and it also is a fertile diamond source rock. In contrast to matrix minerals in magma-borne xenoliths, inclusions in diamond are shielded from external fluids, retaining more pristine information on the state of the eclogite source at the time of encapsulation. Vanadium is a multi-valent element and a widely used elemental redox proxy. Here, we show that that xenolithic garnet has lower average V abundances than garnet inclusions. This partly reflects crystal-chemical controls, whereby higher average temperatures recorded by inclusions, accompanied by enhanced Na2O and TiO2 partitioning into garnet, facilitate V incorporation at the expense of clinopyroxene. Unexpectedly, although diamond formation is strongly linked to metasomatism and xenoliths remained open systems, V concentrations are similar for bulk eclogites reconstructed from inclusions and from xenoliths. This suggests an oxygen-conserving mechanism for eclogitic diamond formation, and implies that eclogite is an efficient system to buffer fO2 over aeons of lithospheric mantle modification by subduction-derived and other fluids.
Abstract
The mineralogy, chemical composition, and physical properties of cratonic mantle eclogites with oceanic crustal protoliths can be modified by secondary processes involving interaction with fluids and melts, generated in various slab lithologies upon subduction (auto‐metasomatism) or mantle metasomatism after emplacement into the cratonic lithosphere. Here we combine new and published data to isolate these signatures and evaluate their effects on the chemical and physical properties of eclogite. Mantle metasomatism involving kimberlite‐like, ultramafic carbonated melts (UM carbonated melts) is ubiquitous though not pervasive, and affected between ~20% and 40% of the eclogite population at the various localities investigated here, predominantly at ~60–150 km depth, overlapping cratonic midlithospheric seismic discontinuities. Its hallmarks include lower jadeite component in clinopyroxene and grossular component in garnet, an increase in bulk‐rock MgO ± SiO2, and decrease in FeO and Al2O3 contents, and LREE‐enrichment accompanied by higher Sr, Pb, Th, U, and in part Zr and Nb, as well as lower Li, Cu ± Zn. This is mediated by addition of a high‐temperature pyroxene from a UM carbonated melt, followed by redistribution of this component into garnet and clinopyroxene. As clinopyroxene‐garnet trace‐element distribution coefficients increase with decreasing garnet grossular component, clinopyroxene is the main carrier of the metasomatic signatures. UM carbonated melt‐metasomatism at >130–150 km has destroyed the diamond inventory at some localities. These mineralogical and chemical changes contribute to low densities, with implications for eclogite gravitational stability, but negligible changes in shear‐wave velocities, and, if accompanied by H2O‐enrichment, will enhance electrical conductivities compared to unenriched eclogites.
Plain Language Summary
Oceanic crust formed at spreading ridges is recycled in subduction zones and undergoes metamorphism to eclogite. Some of this material is captured in the overlying lithospheric mantle, where it is exhumed by passing magmas. Having formed in spreading ridges, these eclogites have proven invaluable archives for the onset of plate tectonics, for the construction of cratons during subduction/collision, as probes of the convecting mantle from which their precursors formed, and as generators of heterogeneity upon recycling into Earth's convecting mantle. During subduction and until exhumation, interaction with fluids and melts (called metasomatism) can change the mineralogy, chemical composition, and physical properties of mantle eclogites, complicating their interpretation, but a comprehensive study of these effects is lacking so far. We investigated mantle eclogites from ancient continents (cratons) around the globe in order to define hallmarks of metasomatism by subduction‐related fluids and small‐volume ultramafic carbonated mantle melts. We find that the latter is pervasive and occurs predominantly at midlithospheric depths where seismic discontinuities are detected, typically causing diamond destruction and a reduction in density. This has consequences for their gravitational stability and for the interpretation of shearwave velocities in cratons.
The metasomatised continental mantle may play a key role in the generation of some ore deposits, in particular mineral systems enriched in platinum-group elements (PGE) and Au. The cratonic lithosphere is the longest-lived potential source for these elements, but the processes that facilitate their pre-concentration in the mantle and their later remobilisation to the crust are not yet well-established. Here, we report new results on the petrography, major-element, and siderophile- and chalcophile-element composition of native Ni, base metal sulphides (BMS), and spinels in a suite of well-characterised, highly metasomatised and weakly serpentinised peridotite xenoliths from the Bultfontein kimberlite in the Kaapvaal Craton, and integrate these data with published analyses. Pentlandite in polymict breccias (failed kimberlite intrusions at mantle depth) has lower trace-element contents (e.g., median total PGE 0.72 ppm) than pentlandite in phlogopite peridotites and Mica-Amphibole-Rutile-Ilmenite-Diopside (MARID) rocks (median 1.6 ppm). Spinel is an insignificant host for all elements except Zn, and BMS and native Ni account for typically <25% of the bulk-rock PGE and Au. High bulk-rock Te/S suggest a role for PGE-bearing tellurides, which, along with other compounds of metasomatic origin, may host the missing As, Ag, Cd, Sb, Te and, in part, Bi that are unaccounted for by the main assemblage.
The close spatial relationship between BMS and metasomatic minerals (e.g., phlogopite, ilmenite) indicates that the lithospheric mantle beneath Bultfontein was resulphidised by metasomatism after initial melt depletion during stabilisation of the cratonic lithosphere. Newly-formed BMS are markedly PGE-poor, as total PGE contents are <4.2 ppm in pentlandite from seven samples, compared to >26 ppm in BMS in other peridotite xenoliths from the Kaapvaal craton. This represents a strong dilution of the original PGE abundances at the mineral scale, perhaps starting from precursor PGE alloy and small volumes of residual BMS. The latter may have been the precursor to native Ni, which occurs in an unusual Ni-enriched zone in a harzburgite and displays strongly variable, but overall high PGE abundances (up to 81 ppm). In strongly metasomatised peridotites, Au is enriched relative to Pd, and was probably added along with S. A combination of net introduction of S, Au +/− PGE from the asthenosphere and intra-lithospheric redistribution, in part sourced from subducted materials, during metasomatic events may have led to sulphide precipitation at ~80–120 km beneath Bultfontein. This process locally enhanced the metallogenic fertility of this lithospheric reservoir. Further mobilisation of the metal budget stored in these S-rich domains and upwards transport into the crust may require interaction with sulphide-undersaturated melts that can dissolve sulphides along with the metals they store.
Towards the goal to understand the role of land-surface processes over the Indian sub-continent, a series of soil-moisture sensitivity simulations have been performed using a non-hydrostatic regional climate model COSMO-CLM. The experiments were driven by the lateral boundary conditions provided by the ERA-Interim (ECMWF) reanalysis. The simulation results show that the pre-monsoonal soil moisture has a significant influence on the monsoonal precipitation. Both, positive and negative soil-moisture precipitation (S-P) feedback processes are of importance. The negative S-P feedback process is especially influential in the western and the northern parts of India.
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.
The impact of precipitation in shallow cumulus convection on the moisture variance and third-order moments of moisture is investigated with the help of large-eddy simulations. Three idealized simulations based on the Rain in Cumulus over the Ocean field experiment are analyzed: one nonprecipitating, on a smaller domain, and two precipitating cases, on a larger domain with different initial profiles of moisture. Results show that precipitation and the associated cloud organization lead to increased generation of higher-order moments (HOM) of moisture compared to the nonprecipitating case. To understand the physical mechanism and the role of individual processes in this increase, budgets of HOM of moisture are studied. Microphysics directly decreases the generation of HOM of moisture, but this effect is not dominant. The gradient production term is identified as the main source term in the HOM budgets. The influence of the gradient production term on moisture variance is further examined separately in cloud active and nonactive regions. The main contribution to the gradient production term comes from the smaller cloud active region because of the stronger moisture flux. Further analyses of the horizontal and vertical cross sections of moisture fluctuations show that the precipitation-induced downdrafts and updrafts are the main mechanism for the generation of moisture variance. The variance increase is linked to shallow dry downdraft regions with horizontal divergence in the subcloud layer, moist updrafts with horizontal convergence in the bulk cloud layer, and finally wider areas of horizontal divergence in the cloud inversion layer.
Teleconnections of the Quasi-Biennial Oscillation in a multi-model ensemble of QBO-resolving models
(2021)
The Quasi-biennial Oscillation (QBO) dominates the interannual variability of the tropical stratosphere and influences other regions of the atmosphere. The high predictability of the QBO implies that its teleconnections could lead to increased skill of seasonal and decadal forecasts provided the relevant mechanisms are accurately represented in models. Here modelling and sampling uncertainties of QBO teleconnections are examined using a multi-model ensemble of QBO-resolving atmospheric general circulation models that have carried out a set of coordinated experiments as part of the Stratosphere-troposphere Processes And their Role in Climate (SPARC) QBO initiative (QBOi). During Northern Hemisphere winter, the stratospheric polar vortex in most of these models strengthens when the QBO near 50 hPa is westerly and weakens when it is easterly, consistent with, but weaker than, the observed response. These weak responses are likely due to model errors, such as systematically weak QBO amplitudes near 50 hPa, affecting the teleconnection. The teleconnection to the North Atlantic Oscillation is less well captured overall, but of similar strength to the observed signal in the few models that do show it. The models do not show clear evidence of a QBO teleconnection to the Northern Hemisphere Pacific-sector subtropical jet.
This thesis aims to analyse in a first step the physical and chemical properties of soil profiles along pedomorphological transects in different land used conditions (protected, partly protected as well as cultivated and pastured areas) in North West Benin and in South East Burkina Faso. The information about soils, which are carried out in consideration of the pedogenesis processes like weathering types, saprolitisation, formation of laterite crusts and denudation within the planation surfaces are therefore correlated in a second step with the structure and dynamic of woody plant around individual soil profiles. The relationship soil properties and woody plant is investigated in order to assess the reciprocal influence between the diversity of woody plants and soil characteristics within a small scale study and under different land use conditions.
A common vertical and lateral differentiation of physical and chemical properties regardless of the partly protected, protected and cultivated status of the sites can be noticed. Thus, in the cultivated site of Kikideni and in the partly protected zone of Natiabouani (South East Burkina Faso) sandy loam and sandy clay loam soil surfaces are widespread because of the occurrence of similar erosion processes like sheet wash, rill and gully erosion while in the central part of the Pendjari National Park loamy soil textures are prevailing. In fact, the steepness of the relief and the length of the slopes in the Pendjari Park seem to limit the development of some erosion forms as gully. Furthermore, the classification of soils reflects the variation of pedological processes along the transects and thus the occurrence of different soil types. The status of the sites may play an insignificant role in the differentiation of soil properties within the scale of small pedomorphological transects. A direct comparison of the vegetation type in the land use respectively partly protected and in the total protected sites (National Park of Pendjari) reveals a transition from the shrub savanna to the tree savanna. In conclusion it is important to insist on the fact that the variations of soil parameters within small slopes and the different sites are more conditioned by varying erosion processes and drainage conditions than the status protected or land use sites while the composition and diversity of plants is influenced by the status of the sites, the prevailing management tools, the pedogenetic conditions as well as the presence of wild animals like elephants. The ordination diagram shows that the organic matter is better correlated to the subgroup representing principally the sites of the hunting zone of the Pendjari Park and might be an explaining factor to the distribution of these sample sites groups. CEC ratios in the partly protected site of Natiabouani represent the highest measured in all sites. Nevertheless, statistical analysis of the CCA (canonical correspondence analysis) indicates generally a low correlation. This tendency is consolidated by the Monte Carlo test (p=0.14) which is a good indicator of species and environmental conditions. The detailed analysis of soil properties and the vegetation dynamic as well as their relationship within small pedomorphological transects represent an important pedological and botanical data collection involving different compartments. This thesis contributes to the better understanding of the savanna landscapes of West Africa and may provide essential scientific background for each development project directed towards interdisciplinary and integrative researches.
One of the most important events in human history occurred during the Early Pleistocene: the dispersal of early hominins out of Africa and into Europe and Asia. In Western Europe, the earliest evidences of the genus Homo have been found in the Baza Basin, at the sites of Orce in the SE of the Iberian Peninsula. These sites contain fossils and lithic industry dated approximately as 1.4–1.3 Ma.While hominin remains and artifacts at Orce, as well as the accompanying fauna, have been extensively studied, the properties and evolution of the Early Pleistocene vegetation in the basin remain unknown. The general effect of climate change on the expansion of early hominins from Africa into Eurasia still remains unclear. It is not known if the Early Pleistocene climate changes and the development of glacials periods led to the extirpation of European communities, or if those communities were able to endure and persist through such adverse climatic periods. This open question highlights the need for climate and environmental analyses for the time before, during and after the first presence of Homo in Europe. This PhD thesis contributes to that need by the presentation of the first long pollen record of the Baza Basin, where the oldest hominin sites in Western Europe are found.
The current state of research about ancient settlements within the Nile Delta allows the hypothesizing of fluvial connections to ancient settlements all over the Nile Delta. Previous studies suggest a larger Nile branch close to Kom el-Gir, an ancient settlement hill in the northwestern Nile Delta. To contribute new knowledge to this little-known site and prove this hypothesis, this study aims at using small-scale paleogeographic investigations to reconstruct an ancient channel system in the surroundings of Kom el-Gir. The study pursues the following: (1) the identification of sedimentary environments via stratigraphic and portable X-ray fluorescence (pXRF) analyses of the sediments, (2) the detection of fluvial elements via electrical resistivity tomography (ERT), and (3) the synthesis of all results to provide a comprehensive reconstruction of a former fluvial network in the surroundings of Kom el-Gir. Therefore, auger core drillings, pXRF analyses, and ERT were conducted to examine the sediments within the study area. Based on the evaluation of the results, the study presents clear evidence of a former channel system in the surroundings of Kom el-Gir. Thereby, it is the combination of both methods, 1-D corings and 2-D ERT profiles, that derives a more detailed illustration of previous environmental conditions which other studies can adopt. Especially within the Nile Delta which comprises a large number of smaller and larger ancient settlement hills, this study's approach can contribute to paleogeographic investigations to improve the general understanding of the former fluvial landscape.