Global Change Abstracts The Swiss Contribution - SCNAT

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164 Global Change Abstracts – The Swiss Contribution | Past Global Changes 08.1-327 Carbon dioxide release from the North Pacific abyss during the last deglaciation Galbraith E D, Jaccard S L, Pedersen T F, Sigman D M, Haug G H, Cook M, Southon J R, Francois R Canada, USA, Switzerland Paleontology , Meteorology & Atmospheric Sciences , Oceanography Atmospheric carbon dioxide concentrations were significantly lower during glacial periods than during intervening interglacial periods, but the mechanisms responsible for this difference remain uncertain. Many recent explanations call on greater carbon storage in a poorly ventilated deep ocean during glacial periods(1-5), but direct evidence regarding the ventilation and respired carbon content of the glacial deep ocean is sparse and often equivocal(6). Here we present sedimentary geochemical records from sites spanning the deep subarctic Pacific that-together with previously published results(7)- show that a poorly ventilated water mass containing a high concentration of respired carbon dioxide occupied the North Pacific abyss during the Last Glacial Maximum. Despite an inferred increase in deep Southern Ocean ventilation during the first step of the deglaciation (18,000-15,000 years ago)(4,8), we find no evidence for improved ventilation in the abyssal subarctic Pacific until a rapid transition similar to 14,600 years ago: this change was accompanied by an acceleration of export production from the surface waters above but only a small increase in atmospheric carbon dioxide concentration (8). We speculate that these changes were mechanistically linked to a roughly coeval increase in deep water formation in the North Atlantic (9-11), which flushed respired carbon dioxide from northern abyssal waters, but also increased the supply of nutrients to the upper ocean, leading to greater carbon dioxide sequestration at mid-depths and stalling the rise of atmospheric carbon dioxide concentrations. Our findings are qualitatively consistent with hypotheses invoking a deglacial flushing of respired carbon dioxide from an isolated, deep ocean reservoir(1-5,12), but suggest that the reservoir may have been released in stages, as vigorous deep water ventilation switched between North Atlantic and Southern Ocean source regions. Nature, 2007, V449, N7164, OCT 18, pp 890-U9. 08.1-328 Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis Galfetti T, Hochuli P A, Brayard A, Bucher H, Weissert H, Vigran J O Switzerland, France Meteorology & Atmospheric Sciences , Paleontology , Geology One of the most important carbon cycle perturbations following the end-Permian mass extinction event straddles the Smithian-Spathian boundary (SSB) (Olenekian, Early Triassic). This anomaly is characterized by a prominent positive carbon isotope excursion known from Tethyan marine rocks. Its global significance is established here by a new high paleolatitude record (Spitsbergen). Paleontological evidence, such as Boreal palynological data (Barents Sea, Norway) and global patterns of ammonoid distribution, indicates a synchronous major change in terrestrial and marine ecosystems near the SSB. The reestablishment of highly diverse plant ecosystems, including the rise of woody gymnosperms and decline of the formerly dominating lycopods, is interpreted as an effect of a major climate change. This hypothesis is supported by modeling of ammonoid paleobiogeography, the distribution patterns of which are interpreted as a proxy for sea surface temperatures (SST). The latest Smithian thus appears to have been a time of a warm and equable climate as expressed by an almost flat pole to equator SST gradient. In contrast, the steep Spathian SST gradient suggests latitudinally differentiated climatic conditions. We propose that this drastic climate change and the global carbon cycle perturbation were triggered by a massive end-Smithian CO 2 injection. The SSB event could therefore represent one of the causes for stepwise and delayed recovery of marine and terrestrial biotas in the wake of the end- Permian biotic crisis. Geology, 2007, V35, N4, APR, pp 291-294. 08.1-329 Dating of syngenetic ice wedges in permafrost with Cl-36 Gilichinsky D A, Nolte E, Basilyan A E, Beer J, Blinov A V, Lazarev V E, Kholodov A L, Meyer H, Nikolskiy P A, Schirrmeister L, Tumskoy V E Russia, Germany, Switzerland Cryology / Glaciology , Paleontology A new method of permafrost dating with the cosmogenic radionuclide Cl-36 is presented. In the first application, syngenetic ice wedges are dated using the ratio of Cl-36 and Cl concentrations in ice as the signal. Cl-36 is produced in the atmo-
Global Change Abstracts – The Swiss Contribution | Past Global Changes sphere by nuclear reactions of cosmic rays on argon. Stable chlorine enters the atmosphere from the oceans. Their ratio does not depend on chloride concentration in precipitations and on sublimation of snow. In situ production of Cl-36 in permafrost ice via cosmic ray-induced reactions and neutron capture are calculated and the dating age limit is estimated as 3 million years. Cl-36/ Cl ratios in permafrost samples from cape Svyatoy Nos (Laptev Sea coast), North-Eastern Siberia, are measured by accelerator mass spectrometry. Analysis of the first results and the calculated dates support the feasibility of the Cl-36 permafrost dating method. Quaternary Science Reviews, 2007, V26, N11-12, JUN, pp 1547-1556. 08.1-330 Assimilation of the plutonic roots of the Andean arc: Evidence from CO 2-rich fluid inclusions in olivines Ginibre C, Dungan M A Switzerland Geochemistry & Geophysics , Geology , Paleontology Geochimica et Cosmochimica Acta, 2007, V71, N15, AUG, SS, p A325. 08.1-331 Paleoecology of Late Carboniferous phylloid algae in southern Guizhou, SW China Gong E, Mang Y, Guan C, Samankassou E, Sun B, Sun B L Peoples R China, Switzerland Ecology , Paleontology , Marine & Freshwater Biology Phylloid algae are important reef-builders in the late Carboniferous. This paper focuses on the paleoecology of phylloid algae in the Late Carboniferous on well-exposed reefs in Ziyun County, Guizhou Province. Phylloid algae growing closely packed are attached via holdfast or similar structure to substrate. They were growing in environments such as shallow water, photic zone and below the wave base with medium energy currents. They have a variety of morphological forms, such as single cup-shaped, cabbage-shaped and clustering cup-shaped. The thalli are of certain tenacity and intensity. In the areas dominated by phylloid algae, other marine organisms are relatively scarce. Obviously, phylloid algae are stronger competitors for living space than other co-occurring organisms. Acta Geologica Sinica English Edition, 2007, V81, N4, AUG, pp 566-572. 165 08.1-332 Late Quaternary river development in the southwest Chad Basin: OSL dating of sediment from the Komadugu palaeofloodplain (northeast Nigeria) Gumnior M, Preusser F Switzerland, Germany Paleontology , Geology , Hydrology The Komadugu river system is the major Nigerian tributary to Lake Chad. its large alluvial complex represents an important archive of the late Quaternary environmental history of the Chad Basin. Modern floodplains are incised into an older fluvial terrace that extends over 5000 km(2). Evidence from satellite images suggests that the ancient river system was dammed up by the Bama Beach Ridge during high stands of mega Lake Chad. This caused the formation of extensive wetlands with a chaotic network of relic channels. The first set of luminescence ages presented here fits well, into the previously established environmental history of the Chad Basin. Both the early and mid-Holocene pluvial periods as well as a final relatively humid period during the late Holocene are reflected by point bar to overbank deposits or channel fills. The onset of the Holocene was characterised by erosion of older dune fields as indicated by grain- size distributions of the alluvium. Satellite images and sedimentological observations show that the floodplain was dominated by meandering channels shifted by frequent avulsion, reflecting a high variability in precipitation and discharge patterns at the beginning and end of Holocene humid periods. Journal of Quaternary Science, 2007, V22, N7, OCT, pp 709-719. 08.1-333 Radiocarbon ages of soil charcoals from the southern Alps, Ticino Switzerland Hajdas I, Schlumpf N, Minikus Stary N, Hagedorn F, Eckmeier E, Schoch W, Burga C, Bonani G, Schmidt M W I, Cherubini P Switzerland Agriculture, Soil Sciences , Geochemistry & Geophysics , Forestry , Plant Sciences , Paleontology Radiocarbon dating of macroscopic charcoal is a useful toot for paleocliniatic and paleoecologic reconstructions. Here we present results of C-14 dating of charcoals found in charcoal-rich soils of Ticino and the Misox Valley (southern Switzerland) which indicate that the Late Glacial and early Holocene fires coincided with warm phases in the North Atlantic region and low lake levels in the Central Europe. Late Holocene charcoals found in these soils document an earlier than believed
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