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Geowissenschaften

Die Erforschung der Erdgeschichte erfüllt den grundlegenden menschlichen Drang zu wissen, wie die Welt entstanden ist. Im Laufe ihrer 4,6 Milliarden Jahre langen Geschichte hat die Erde eine enorme Transformation durchlaufen, und die Stabilisotopenanalyse steht bei der Erforschung dieser Veränderungsprozesse an vorderster Front. Durch das Verständnis der makro- und mikrozyklischen Mechanismen, welchen die leichten stabilen Isotope in der Lithosphäre durch natürliche Prozesse unterliegen, wächst auch unser Wissen über die Erdgeschichte kontinuierlich.

Paläoklima

Eine der ersten Anwendungen der Stabilisotopenmassenspektrometrie leichter Elemente war die Rekonstruktion des Paläoklimas auf Grundlage der Sauerstoff-Isotopenzusammensetzung (δ18O) von sehr alten, konservierten marinen Carbonaten. Auch heute noch ist dies eine der weitverbreitesten Methoden zur Erforschung der Klimageschichte der Erde. Dieses Paläothermometer basiert auf dem Grundprinzip, dass die Fraktionierung von Sauerstoffisotopen in Calcit temperaturabhängig ist. Das isoprime precisION mit Dual Inlet und MultiCarb ermöglicht eine sehr präzise und zuverlässige, automatisierte Messung von Carbonaten, ideal zur Erzeugung hochauflösender Paläotemperaturaufzeichnungen.

Kosmologie

Die Schwefelisotopenanalyse von extraterrestrischen Sulfidmineralien, z.B. von Meteoriten, hat eine Vielzahl von Erkenntnissen über den Ursprung der Erde und des Sonnensystems ermöglicht. Die Isotopenzusammensetzung von meteoritischem Schwefel (Canyon Diabolo Triolite) wurde auch als der ursprüngliche Bezugspunkt für Erdkruste und -mantel verwendet, von der ausgehend die globalen Fraktionen im Schwefelkreislauf evaluiert werden. Schwefelhaltige Mineralien lassen sich leicht mit unserem vielseitigen Spektrum von EA-IRMS-Systemen analysieren, welche die Advanced Purge and Trap Technologie (APT) für eine unschlagbare Trennung und Peakfokussierung von SO2 nutzen, um eine perfekte Auflösung und eine unvergleichliche Empfindlichkeit für die Mineralschwefelanalyse zu gewährleisten.

Stratigraphie

δ13C-Fluktuationen im Laufe geologischer Zeitalter werden durch Änderungen des Gleichgewichts im Kohlenstoffkreislauf bewirkt. Da die Verweilzeit im Kohlenstoffkreislauf kurz ist (10 ka), werden Änderungen im Kohlenstofffluss im Sediment sehr genau global aufgezeichnet. Als solche sind gelegentliche Spikes im globalen δ13C als stratigraphische Marker für die Chemostratigraphie nützlich, besonders während des Paläozoikums. Der iso FLOW nutzt unsere neuartige UltiTrap-Technologie und ermöglicht so eine präzise, durchgängige Continuous Flow Analyse von Massencarbonaten, um solche Isotopenabweichungen zu identifizieren.

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248 Ergebnisse:

Relict soil evidence for profound quaternary aridification of the Atacama Desert, Chile
Geoderma (2016)
Angela Ebeling, Erik Oerter, J.W. Valley, Ronald Amundson

A relict soil on a late Tertiary/early Quaternary gravelly alluvial fan in the southern Atacama Desert was studied to determine if evidence of Quaternary climate change was evident in the profile. Stratigraphic relations of soil morphological features indicated that the initial phase of soil development was extensive chemical weathering with the loss of Si, Na, etc. and the formation of secondary clay. This was then followed by a prolonged period of carbonate accumulation that has discontinuously impregnated the earlier formed argillic horizons. The carbonate accumulation occurred both as fine-grained accumulations that engulfed and expanded the gravelly soil matrix, and as carbonate that formed dense and continuous coatings on gravel bottoms. Overlying the carbonate is a Holocene calcareous sand unit. Stable C and O isotope profiles of the disseminated carbonate show that this material appears to have formed under conditions of low to modest plant cover and significant soil water evaporation, very similar to soils presently found at higher latitudes and altitudes in modern Argentina. Seven transects of the carbonate laminations on the gravels at 10-μm scale reveal that all show a nearly 4‰ increase in δ13C values with time over distances of approximately 150mm, and variable δ18O values. The shift in C isotope values, which is unlikely to be due to significant changes in C3 vs. C4 vegetation, reflects a profound and prolonged aridification with a corresponding lowering of plant density and soil respiration. The precise beginning of the aridification is unknown due to a lack of carbonate dating methods amenable to the time frame involved. When all changes are considered, this remarkable soil indicates that local rainfall declined from somewhere between 500 to 1000mm y−1 in the late Tertiary/early Quaternary, to the present climate of about 25mm y−1. Future work will focus on developing more precise geochronological controls, but this initial study reveals the enormous potential that carbonate-bearing relict soils have for understanding climate change.
Schlagworte: carbon , oxygen , soil , geol , mulitcarb

Seasonality fluctuations recorded in fossil bivalves during the early Pleistocene: Implications for climate change
Palaeogeography, Palaeoclimatology, Palaeoecology (2016)
Gaia Crippa, L. Angiolini, C. Bottini, E. Erba, F. Felletti, C. Frigerio, J.A.I. Hennissen, M.J. Leng, M.R. Petrizzo, I. Raffi, G. Raineri, M.H. Stephenson

Understanding the transformations of the climate system may help to predict and reduce the effects of global climate change. The geological record provides a unique archive that documents the long-term fluctuations of environmental variables, such as seasonal change. Here, we investigate how seasonal variation in seawater temperatures varied in the Mediterranean Sea during the early Pleistocene, approaching the Early-Middle Pleistocene Transition (EMPT) and the beginning of precession-driven Quaternary-style glacial–interglacial cycles. We performed whole-shell and sclerochemical stable isotope analyses (δ18O, δ13C) on bivalves, collected from the lower Pleistocene Arda River marine succession (northern Italy), after checking shell preservation. Our results indicate that seawater temperature seasonality was the main variable of climate change in the Mediterranean area during the early Pleistocene, with the Northern Hemisphere Glaciation (NHG) exerting a control on the Mediterranean climate. We show that strong seasonality (14.4–16.0°C range) and low winter paleotemperatures (0.8–1.6°C) were likely the triggers leading to the establishment of widespread populations of so called “northern guests” (i.e., cold water taxa) in the Mediterranean Sea around 1.80Ma. The shells postdating the arrival of the “northern guests” record a return to lower seasonal variations and higher seawater paleotemperatures, with seasonality increasing again approaching the EMPT; the latter, however, is not associated with a corresponding cooling of mean seawater paleotemperatures, showing that the observed seasonality variation represents a clear signal of progressive climate change in the Mediterranean Sea.
Schlagworte: carbon , oxygen , geol , clim , mulitcarb

Stable isotopes in guano: Potential contributions towards palaeoenvironmental reconstruction in Tabon Cave, Palawan, Philippines
Quaternary International (2016)
O. Choa, M. Lebon, X. Gallet, E. Dizon, W. Ronquillo, S.C. Jago-on, F. Détroit, C. Falguères, B. Ghaleb, F. Sémah

Tabon Cave is a key site for the understanding of modern human dispersals in the Philippine archipelago and Island Southeast Asia. Nestled in the karst landscape that borders the southwestern coast of Palawan, it has delivered the earliest confirmed Homo sapiens remains in the Philippines dating to the late Pleistocene, as far back as around 47 ka. Among other methods, the broad characteristics of the environment in which these humans once lived may be drawn using stable isotope analysis of the rich guano deposits in the cave, an approach that follows a growing number of studies indicating the potential of guano as a palaeoenvironmental archive. δ13C values reveal the general prevalence of C3 forest tempered by savannah woodland with grassland contributions both well before and slightly after a securely-dated fireplace at 32 ka; the lower interval would refer to OIS 3 or older interglacial periods, while the upper interval would refer to the transition either before or after the Last Glacial Maximum. No useful conclusions are drawn from δ15N results due to suspected ammonia fractionation. Pending future dating efforts for confirmation, this preliminary study contributes to the development of an alternative and promising palaeoenvironmental proxy and hopes to shed further light on the prehistoric odysseys that took place across Island Southeast Asia.
Schlagworte: carbon , nitrogen , geol , arch , clim , elem

Clay mineralogical and geochemical expressions of the “late Campanian event” in the Aquitaine and Paris basins (France): Palaeoenvironmental implications
Palaeogeography, Palaeoclimatology, Palaeoecology (2016)
E. Chenot, P. Pellenard, M. Martinez, J.-F. Deconinck, P. Amiotte-Suchet, N. Thibault, L. Bruneau, T. Cocquerez, R. Laffont, E. Pucéat, F. Robaszynski

Campanian sediments from two French sedimentary basins were studied, using clay mineralogy and stable isotope (δ13C and δ18O) geochemistry, in order to investigate the Late Campanian Event. The clay fraction of the Campanian sediments from the Tercis-les-Bains section (Aquitaine Basin) and from the Poigny borehole (Paris Basin) is mainly composed of smectite. This background sedimentation was, however, interrupted during the Upper Campanian in the two basins by a substantial increase in detrital inputs, including illite, kaolinite, and chlorite at Tercis-les-Bains, and illite at Poigny. This detrital event, resulting from the enhanced erosion of nearby continental areas triggered by increasing runoff, has also been recognized in the Tethys and South Atlantic oceans. It coincided with a global negative carbon isotope excursion, the Late Campanian Event (LCE). Carbon isotope stratigraphy was used to correlate the two basins with previously studied sections from distant areas. Spectral analysis of the bulk δ13C from Tercis-les-Bains suggests a duration of ca. 400kyr for a pre-LCE negative excursion and ca. 800–900kyr for the LCE sensu stricto. The detrital event, as characterized by clay mineralogy, spans the interval that comprises the pre-LCE and the LCE, with a duration of 1.3Myr. Intensification of continental erosion during the LCE may have resulted either from the Late Campanian polyplocum regression and/or from a regional tectonic pulse that triggered the emersion of previous submerged shelf areas and the increase of silicate erosion. As the LCE seems to be recorded at a large geographic scale, it is proposed here that enhanced chemical weathering and an associated decrease in atmospheric pCO2 levels could have contributed to the long-term Late Cretaceous cooling trend.
Schlagworte: carbon , oxygen , geol , mulitcarb

Climate change and human activities over the past millennium at Mt. Jeombong, central-eastern Korea
Geosciences Journal (2016)
Inseok Chae, Jungjae Park

We present a multi-proxy record (pollen, microscopic charcoal, carbon-isotopic composition [δ13C], organic content, and particle size) of the late-Holocene climate change and human impact from central-eastern South Korea. The Medieval Climate Anomaly (MCA) and Little Ice Age (LIA), the most recent major climate events, have not been accurately investigated by paleolimnological studies in Korea, mainly due to a lack of undisturbed sediments and indifference to the past climate change. Our pollen records show late- Holocene centennial climate variations characterized by the successive solar minimums of the Oort, Wolf, Spörer, Maunder, and Dalton. We find paleoenvironmental evidence for shifting cultivation associated with serious droughts and consequent famines during the early 19th-century Dalton minimum. Our interpretation of human activities is well supported by Korean historical documents describing socioeconomic suffering induced by LIA climate deteriorations.
Schlagworte: carbon , geol , clim , elem

Origin of pegmatites and fluids at Ponta Negra (RJ, Brazil) during late- to post-collisional stages of the Gondwana Assembly
Lithos (2016)
Everton Marques Bongiolo, Christophe Renac, Patricia d'Almeida de Toledo Piza, Renata da Silva Schmitt, André Sampaio Mexias

The Ponta Negra Pegmatites (PNP), part of a pegmatitic province in Rio de Janeiro State, Brazil, crop out along an intensely deformed, medium- to high-grade metamorphic area that is proximal to a crustal-scale thrust zone developed during the Brasiliano/Pan–African Orogeny. Fieldwork shows that the pegmatites formed in two distinct stages: (i) syn-collisional leucosome veins (Group I) conformable with the tectonic foliation of the gneissic host rocks and (ii) late- to post-collisional dykes (Group II) that cross-cut the same tectonic foliation at a high angle. In this paper, we use geochemistry of whole-rock and mineral separates (alkali–feldspar and biotite), fluid inclusion microthermometry and stable isotopic (δ18O, δD, δ13C) determinations on minerals (quartz, alkali–feldspar, biotite and magnetite) and fluid inclusions to provide insights into the composition of the pegmatite-forming melts, associated fluids, and their geotectonic significance. U–Pb SHRIMP dating of the Cajú syenogranite was performed to evaluate and compare the timing of magmatic events along the Cabo Frio Tectonic Domain as this is the closest post-collisional pluton to the studied pegmatites. The calculated temperature for the Group I syn-collisional veins (740°C) is similar to previous estimates for the peak metamorphic conditions in the study area. Variations in the temperature of the Group II pegmatite dykes obtained from stable isotopes (380 to 720°C), and microthermometric data from primary fluid inclusions with traces of N2 (Th=280 to 360°C), may reflect the thermodynamics of the pegmatite crystallization, exsolution textures and isotopic exchange. The composition of fluids in equilibrium within the pegmatite dykes consists of magmatic and metamorphic components. The minimum pressures calculated for the emplacement of the pegmatites are equivalent to a shallow crustal depth between 1.7 and 3.5km, which corresponds to the exhumation of the orogen since the emplacement of the pegmatites. A linear trend of decreasing CO2 content and δ13CCO2 is consistent with mixtures between (i) carbon derived from organic matter or volatilization of skarns and (ii) inorganic carbon (carbonate). Based on the data obtained, we propose that the pegmatites of Ponta Negra are close to an LCT-type geochemical signature (highly peraluminous magmas with normative corundum), and originated by partial melting of the metasedimentary Palmital succession at depth, during the waning stages of the Búzios Orogeny. The primary melts of the PNP cross-cut both the Neoproterozoic supracrustals and the Paleoproterozoic orthogneissic basement during its ascent and emplacement at higher crustal levels. Variable melt sources explain the slight differences in geochemical compositions among the studied rocks within the metasedimentary succession, which probably include Mn-bearing exhalites, as well as differentiation processes. The 454±5Ma U–Pb (zircon) age of the Cajú syenogranite overlaps previous geochronological data of 440±11Ma obtained on a pegmatite dyke at Ponta Negra, bracketing and extending the time interval for the Gondwana assembly collapse magmatism in the region. The heat that triggered this magmatic event could still be a consequence of the collisional orogeny, increasing contents of heat-producing elements, or, a large intraplate extension that followed the Gondwana amalgamation and initiated the formation of Paleozoic basins.
Schlagworte: carbon , hydrogen , oxygen , geol , mulitcarb

Sulfur Geochemistry of a Lacustrine Record from Taiwan Reveals Enhanced Marine Aerosol Input during the Early Holocene
Scientific Reports (2016)
Xiaodong Ding, Dawei Li, Liwei Zheng, Hongyan Bao, Huei-Fen Chen, Shuh-Ji Kao, M. Novak, K. R. Beuning, J. M. Russell, B. Mayer, L. Schwark, G. Mora, L. Hinnov, F. W. Nara, J. M. Russell, J. P. Werne, C. S. Andresen, S. Bjorck, O. Bennike, G. Bond, C. A.

Lacustrine record of marine aerosol input has rarely been documented. Here, we present the sulfur geochemistry during the last deglaciation and early Holocene of a sediment core retrieved from the Dongyuan Lake in southern Taiwan. An unusually high sulfur peak accompanying pyrite presence is observed at 10.5 ka BP. Such high sulfur content in lacustrine record is unusual. The δ34S of sulfur varied from +9.5 to + 17.1‰ with two significant positive shifts at 10.5 and 9.4 ka BP. The sources of sulfur and potential processes involving the sulfur isotope variation including bacterial sulfate reduction, volcanic emissions, in-catchment sulfide oxidation and marine aerosol input are discussed. Enhanced marine aerosol input is the most likely explanation for such sulfur peaks and δ34S shifts. The positive δ34S shifts appeared concurrently with the maximum landslide events over Taiwan resulted from enhanced typhoon activities. The synchronicity among records suggests that increased typhoon activities promoted sea spray, and consequently enhanced the marine aerosol input with 34S-enriched sulfate. Our sulfur geochemistry data revealed sea spray history and marine influence onto terrestrial environment at coastal regions. Wider coverage of spatial-temporal lacustrine sulfur geochemistry record is needed to validate the applicability of sulfur proxy in paleoenvironmental research.
Schlagworte: sulfur , geol , elem

N2 production rates limited by nitrite availability in the Bay of Bengal oxygen minimum zone
Nature Geoscience (2016)
L. A. Bristow, C. M. Callbeck, M. Larsen, M. A. Altabet, J. Dekaezemacker, M. Forth, M. Gauns, R. N. Glud, M. M. M. Kuypers, G. Lavik, J. Milucka, S. W. A. Naqvi, A. Pratihary, N. P. Revsbech, B. Thamdrup, A. H. Treusch, D. E. Canfield

A third or more of the fixed nitrogen lost from the oceans as N2 is removed by anaerobic microbial processes in open ocean oxygen minimum zones. These zones have expanded over the past decades, and further anthropogenically induced expansion could accelerate nitrogen loss. However, in the Bay of Bengal there has been no indication of nitrogen loss, although oxygen levels are below the detection level of conventional methods (1 to 2 μM). Here we quantify the abundance of microbial genes associated with N2 production, measure nitrogen transformations in incubations of sampled seawater with isotopically labelled nitrogen compounds and analyse geochemical signatures of these processes in the water column. We find that the Bay of Bengal supports denitrifier and anammox microbial populations, mediating low, but significant N loss. Yet, unlike other oxygen minimum zones, our measurements using a highly sensitive oxygen sensor demonstrate that the Bay of Bengal has persistent concentrations of oxygen in the 10 to 200 nM range. We propose that this oxygen supports nitrite oxidation, thereby restricting the nitrite available for anammox or denitrification. If these traces of oxygen were removed, nitrogen loss in the Bay of Bengal oxygen minimum zone waters could accelerate to global significance.
Schlagworte: nitrogen , oxygen , geol , gashead

Authigenic 10Be/9Be ratio signature of the Matuyama–Brunhes boundary in the Montalbano Jonico marine succession
Earth and Planetary Science Letters (2016)
Quentin Simon, Didier L. Bourlès, Franck Bassinot, Sébastien Nomade, Maria Marino, Neri Ciaranfi, Angela Girone, Patrizia Maiorano, Nicolas Thouveny, Sandrine Choy, Fabien Dewilde, Vincent Scao, Gulay Isguder, Dominique Blamart

Geomagnetic dipole moment (GDM) lows associated with polarity reversals or geomagnetic excursions induce significant modulation of the cosmogenic nuclide Beryllium-10 (10Be) production. Hence, the reconstruction of atmospheric 10Be production rates from natural archives such as marine sedimentary sequences or ice cores constitutes a complementary approach, independent from paleomagnetic measurements, to decipher past GDM fluctuations. This is particularly important in the Montalbano Jonico succession (South Italy) since it is candidate to host the Global Stratotype Section and Point of the Middle Pleistocene Stage but where the magnetostratigraphic positioning of the Matuyama–Brunhes boundary (MBB) has not been available up to now. This study presents (1) original authigenic 10Be cosmogenic nuclide and 9Be stable isotope results, and (2) new high-resolution benthic oxygen isotope record covering termination IX and Marine Isotope Stage (MIS) 19. A robust chronological framework is established on the basis of (i) our oxygen isotope stratigraphy, using the strong analogies between MIS 1 and MIS 19c in terms of orbital forcing and CO2 level, and (ii) one precise 40Ar/39Ar date obtained in the tephra layer V4. The authigenic 10Be/9Be ratio record marks the atmospheric 10Be overproduction linked to the dipole low accompanying the MBB transition, with a characteristic twofold increase of the 10Be production at the end of MIS 19c and early MIS 19b. This signature is similar to those described in both marine and ice core records. The detailed chronostratigraphy constrained by a radiometrically-dated tephra layer (773.9±1.3 ka) within the MBB interval, makes it possible to discuss the structure and to assess the timing of the 10Be-production changes, and thus the MBB geomagnetic variations, with an unprecedented accuracy for a marine archive (sedimentation rates ∼80 cm/ka). These new cosmogenic nuclide production signatures provide the only missing constraint required for retaining the Montalbano Jonico succession as a global-scale correlation reference section for the Early–Middle Pleistocene boundary.

N2 production rates limited by nitrite availability in the Bay of Bengal oxygen minimum zone
Nature Geoscience (2016)
L. A. Bristow, C. M. Callbeck, M. Larsen, M. A. Altabet, J. Dekaezemacker, M. Forth, M. Gauns, R. N. Glud, M. M. M. Kuypers, G. Lavik, J. Milucka, S. W. A. Naqvi, A. Pratihary, N. P. Revsbech, B. Thamdrup, A. H. Treusch, D. E. Canfield

A third or more of the fixed nitrogen lost from the oceans as N2 is removed by anaerobic microbial processes in open ocean oxygen minimum zones. These zones have expanded over the past decades, and further anthropogenically induced expansion could accelerate nitrogen loss. However, in the Bay of Bengal there has been no indication of nitrogen loss, although oxygen levels are below the detection level of conventional methods (1 to 2 μM). Here we quantify the abundance of microbial genes associated with N2 production, measure nitrogen transformations in incubations of sampled seawater with isotopically labelled nitrogen compounds and analyse geochemical signatures of these processes in the water column. We find that the Bay of Bengal supports denitrifier and anammox microbial populations, mediating low, but significant N loss. Yet, unlike other oxygen minimum zones, our measurements using a highly sensitive oxygen sensor demonstrate that the Bay of Bengal has persistent concentrations of oxygen in the 10 to 200 nM range. We propose that this oxygen supports nitrite oxidation, thereby restricting the nitrite available for anammox or denitrification. If these traces of oxygen were removed, nitrogen loss in the Bay of Bengal oxygen minimum zone waters could accelerate to global significance.
Schlagworte: nitrogen , oxygen , geol , gashead