HR: 1340h
AN: PP33A-0916    [Abstracts]
TI: Do Sm/Nd- and Sr-Isotopic Signals in Lake Baikal Sediments Reflect Shifts in Atmospheric Flow Patterns of Central Eurasia During Termination I ?
AU: * Zopperitsch, M
EM: mzoppi@gfz-potsdam.de
AF: Institute of Geosciences, University Potsdam, PO Box 601553, Potsdam, D-14415 Germany
AU: Hegner, E
EM: hegner@min.uni-muenchen.de
AF: Department of Earth and Environmental Sciences, Ludwig-Maximilians-Universit\"{a}t M\"{u}nchen, Theresienstrasse 41, M\"{u}nchen, D-80333 Germany
AU: Oberh\"{a}nsli, R
EM: roob@geo.uni-potsdam.de
AF: Institute of Geosciences, University Potsdam, PO Box 601553, Potsdam, D-14415 Germany
AU: Romer, R L
EM: romer@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473 Germany
AU: Dulski, P
EM: dulski@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473 Germany
AU: Oberh\"{a}nsli, H
EM: oberh@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, D-14473 Germany
AB: Loess deposits give insights into past climatic and atmospheric conditions, as mineral dust entrainment, transport and deposition is related to humidity distribution (vegetation), wind speed and wind direction. To resolve changing atmospheric conditions and mineral aerosol transport in the northern part of Central Eurasia during the last 20 ka (LGM to present) we investigated a 2 metre long sediment core from Lake Baikal to trace provenance of the inorganic aeolian component. The location of the Lake Baikal sediment core, on a horst structure with hemipelagic sedimentation, is ideally positioned to serve as a dust trap. These sediments show a bimodal grain-size distribution, separating the silt and the clay fraction with the coarse mode falling into the range of 12-14 $\mu$m. While the mode of the coarse fraction remains rather constant with only minor variations during the investigated time interval, the silt/clay-ratio increases from the glacial to the Holocene, together with a parallel increasing proportion of minerals $>$ 20 $\mu$m. This is in contrast to Chinese loess, where the ratio of coarse to fine mode fractions is increased during the glacial periods. Historical reports and TotalOzoneMappingSpectrometer (TOMS) observations confirm that enormous dust events, evolving from the Taklimakan desert and Siberia to the West of the lake, occasionally carry a huge amount of mineral dust in the atmosphere above Lake Baikal. The grain-size distribution of aeolian deposits from the Chinese loess plateau to the Pacific shows a systematic eastward decrease in maximum particle size and thus a decreasing coarse mode of event dust with increasing source distance. Given the distance from the Gobi desert to Lake Baikal at maximum a 12-15 $\mu$m mode fraction is expected to reach the Lake Baikal core location. Modern aerosols, collected on the ice-cover of Central Lake Baikal in early spring 2001 exhibit a monomodal size distribution with a mode of 9 $\mu$m. This is in agreement with a minerogenic aerosol size distribution after several 100 kilometres of transport and supports an aeolian origin of the coarse mode fraction found in the lake sediments. To trace provenance, we used the Sm/Nd-isotopic systematics in combination with the Sr-isotopic ratios and geochemical and mineralogical information. Although trace element characteristics indicate a dominant contribution from Lake Baikal hinterland to the coarse mode fraction, climate change is well documented in the isotopic signature of both the clay and silt fraction, with the principal shift occurring during Termination I. We argue that these isotopic signals reflect a change in sediment provenance rather than a weathering related alteration of mineral associations.
DE: 3344 Paleoclimatology
DE: 3319 General circulation
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
DE: 1015 Composition of the core
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting