Global Change Abstracts The Swiss Contribution - SCNAT

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172 Global Change Abstracts – The Swiss Contribution | Past Global Changes (1) For the last deglaciation and Termination V (the initiation of MIS 11 at around 430 ka) we report high-resolution sedimentary nitrogen isotope (delta N-15)records from Cariaco Basin in the Caribbean Sea. During both terminations the previously reported interglacial decrease in delta N-15 clearly lags local changes such as water column anoxia as well as global increases in denitrification by several thousand years. On top of the glacial-interglacial change, several delta N-15 peaks were observed during the last deglaciation. The deglacial signal in Cariaco Basin can be best explained as a combination of (1) local variations in suboxia and water column denitrification as the reason for the millennial-scale peaks, (2) a deglacial maximum in mean ocean nitrate delta N-15, and (3) increasing N-2 fixation in response to globally increased denitrification causing the overall deglacial delta N-15 decrease. In the Holocene, much of the decrease in delta N-15 occurred between 6 and 3 ka, coinciding with an expected precession-modulated increase in African dust transport to the tropical North Atlantic and the Caribbean. This begs the hypothesis that N-2 fixation in this region increased in response to interglacial maxima in denitrification elsewhere but that this response strengthened with increased mid- Holocene iron input. It remains to be seen whether the data for MIS 11 support this interpretation. Global Biogeochemical Cycles, 2007, V21, N4, DEC 15 ARTN: GB4019. 08.1-353 Grape harvest dates as a proxy for Swiss April to August temperature reconstructions back to AD 1480 Meier N, Rutishauser T, Pfister C, Wanner H, Luterbacher J Switzerland Plant Sciences , Meteorology & Atmospheric Sciences , Paleontology We present an annually resolved record of grape harvest dates for Switzerland. The strong negative relationship between grape harvest dates and April August temperatures allowed a new reconstruction, with associated uncertainties, to be derived back to 1480. Calibration (1928 -1979) was performed with monthly data from the Basel and Geneva stations and verified over 1980 -2006. Twelve days of grape harvest difference correspond to around 1 degrees C April - August temperature difference. Periods cooler (late grape harvest dates) than the 1961 -1990 mean are reconstructed during the 17th century and at the beginning of the 19th century. Warmer conditions were experienced in the early 18th century and during the recent decades, in agreement with grape harvest temperature reconstructions from France and other independent temperature estimates. On decadal (annual) time-scales the earliest harvests were in the 1580s (2003) and the latest vintages in the 1740s (1816). Large tropical volcanic eruptions led to significantly later grape harvest dates (cooling) one to two years after the event. Geophysical Research Letters, 2007, V34, N20, OCT 24 ARTN: L20705. 08.1-354 Evidence of a two-fold glacial advance during the last glacial maximum in the Tagliamento end moraine system (eastern Alps) Monegato G, Ravazzi C, Donegana M, Pini R, Calderoni G, Wick L Italy, Switzerland Paleontology , Cryology / Glaciology , Geomorphology The glacial history of the Tagliamento morainic amphitheater (southeastern Alpine foreland, Italy) during the last glacial maximum (LGM) has been reconstructed by means of a geological survey and drillings, radiocarbon dating and pollen analysis in the amphitheater and in the sandur. Two phases of glacial culmination, separated by a distinct recession, are responsible for glacial landforms and related sediments in the outer part of the amphitheater. The age of the younger advance fits the chronology of the culmination of the last glaciation in the Alps, well established between 24 and 21 cal ka BP (20 to 17.5 C-14 ka BP), whereas the first pulse between 26.5 and 23 cal ka BP (22 to 21 (14C) ka BP), previously undated, was usually related to older (pre-LGM) glaciations by previous authors. Here, the first pulse is the most extensive LGM culmination, but is often buried by the subsequent pulse. The onset and final recession of the late Wurm Alpine glaciation in the Tagliamento amphitheater are synchronous with the established global glacial maximum between 30 and 19 cal ka BP. The two-fold LGM glacial oscillation is interpreted as a millennial-scale modulation within the late Warm glaciation, caused by oscillations in inputs of southerly atmospheric airflows related to Dansgaard-Oeschger cycles. Phases of enhanced southerly circulation promoted increased rainfall and ice accumulation in the southern Alps. Quaternary Research, 2007, V68, N2, SEP, pp 284-302.
Global Change Abstracts – The Swiss Contribution | Past Global Changes 08.1-355 European ammonoid diversity questions the spreading of anoxia as primary cause for the Cenomanian/Turonian (Late Cretaceous) mass extinction Monnet C, Bucher H Switzerland Marine & Freshwater Biology , Geology , Paleontology , Biodiversity Ammonoid diversity patterns show that the spreading of oceanic anoxia is not the initial and major kill mechanism for the Cenomanian /Turonian mass extinction as usually suggested. In the Anglo-Paris Basin and the Vocontian Basin, the drop of ammonoid species richness starts around the middle/late Cenomanian boundary, i.e. 0.75 myr before the occurrence of anoxic deep-water sediments. The stepwise extinction of first heteromorphs and then acanthoceratids is incompatible with the rise of the oxygen minimum zone. Moreover, shelf environments of these basins remained well oxygenated during the Cenomanian/Turonian boundary interval. Thus, we stress that other causative mechanisms initiated the ammonoid extinction even if anoxia subsequently participated in the demise of marine ecosystems. Swiss Journal of Geosciences, 2007, V100, N1, JUN, pp 137-144. 08.1-356 Phosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2 Mort H P, Adatte T, Föllmi K B, Keller G, Steinmann P, Matera V, Berner Z, Stüben D Switzerland, USA, Germany Oceanography , Geology , Geochemistry & Geophysics , Paleontology Four sections documenting the impact of the late Cenomanian oceanic anoxic event (OAE 2) were studied in basins with different paleoenvironmental regimes. Accumulation rates of phosphorus (P) bound to iron, organic matter, and authigenic phosphate are shown to rise and arrive at a distinct maximum at the onset of OAE 2, with an associated increase in delta C-13 values. Accumulation rates of P return to preexcursion values in the interval where the delta C-13 record reaches its first maximum. An offset in time between the maximum in P accumulation and peaks in organic carbon burial, hydrogen indices, and C-org/P-react molar ratios is explained by the evolution of OAE 2 in the following steps. (1) An increase in productivity increased the flux of organic matter and P into the sediments; the preservation of organic matter was low and its oxidation released P, which was predominantly mineralized. (2) Enhanced produc- 173 tivity and oxidation of organic matter created dysoxic bottom waters; the preservation potential for organic matter increased, whereas the sediment retention potential for P decreased. (3) The latter effect sustained high primary productivity, which led to an increase in the abundance of free oxygen in the ocean and atmosphere system. After the sequestration of CO 2 in the form of black shales, this oxygen helped push the ocean back into equilibrium, terminating black shale deposition and removing bioavailable P from the water column. Geology, 2007, V35, N6, JUN, pp 483-486. 08.1-357 The Cenomanian/Turonian anoxic event at the Bonarelli level in Italy and Spain: enhanced productivity and/or better preservation? Mort H, Jacquat O, Adatte T, Steinmann P, Föllmi K B, Matera V, Berner Z, Stüben D Switzerland, Germany Paleontology , Geology , Oceanography The upper Cenomanian pelagic sediments of Furlo in the northern Apennines, Italy, are characterized by a 1.5-m-thick organic-rich stratigraphic horizon called the Bonarelli Level, which represents the second major oceanic anoxic event in the Cretaceous (OAE 2). The Bonarelli Level is depleted in carbonates and consists essentially of biogenic quartz, phyllosilicates, and organic matter, with values of TOC reaching 18%. The age of the Furlo section is constrained by correlating its delta C-13 curve with that of the well-dated Pueblo (USA) and Eastbourne (UK) sections. The presence of all the planktonic foraminiferid zones and details of the OAE 2 delta C-13 excursion indicates a relatively continuous but reduced sedimentation rate across the Cenomanian/Turonian (C/T) boundary. Sediment and TOC mass accumulation rates have been calculated and suggest a sedimentation break in the upper Bonarelli Level. This may be an artifact of the diachronous FAD of the planktonic foraminiferid Helvetoglobotruncana helvetica and suggests that in some sections the delta C-13 curve may provide more reliable age control for dating the C/T boundary. In order quantitatively to explain the carbon isotope curve and the measured TOC mass accumulation rate, a simple dynamic model of the isotope effects of organic versus inorganic carbon burial was developed. In order to verify the consistency of the model we correlated the modeled Output of the Furlo section with that of the Manilva section, in southeast Spain. The modeling shows that increasing productivity only partially explains the measured delta C-13 excursion and is not the only factor relevant to black shales deposition. Preservation may play a
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