HR: 0800h
AN: PP21B-1376    [Abstracts]
TI: Slope Evolution At The Margins Of Lake El'gygytgyn Impact Crater In Late Quaternary Time
AU: * Schwamborn, G
EM: gschwamborn@awi-potsdam.de
AF: Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg A43, Potsdam, 14473 Germany
AU: Fedorov, G
EM: grifed@ramber.ru
AF: Arctic and Antarctic Research Institute, Bering Street, St. Petersburg, 199397 Russian Federation
AU: Meyer, H
EM: hmeyer@awi-potsdam.de
AF: Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg A43, Potsdam, 14473 Germany
AU: Schirrmeister, L
EM: lschirrmeister@awi-potsdam.de
AF: Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg A43, Potsdam, 14473 Germany
AU: Hubberten, H W
EM: hubbert@awi-potsdam.de
AF: Alfred Wegener Institute for Polar and Marine Research, Telegrafenberg A43, Potsdam, 14473 Germany
AB: Periglacial environmental changes are thought to trigger sediment export into Lake El'gygytgyn and we studied the permafrost surrounding and its properties to amend paleoclimate reconstructions using the lake sediment record. We use the following two distinct periglacial formations as complementary paleoenvironmental archives. First, after collecting GPR data for localizing undisturbed sediment layers a five-meter permafrost core was recovered, which penetrated a discrete terrace formation. In contrast to sediment studies in mid and low latitude areas we made use of the chemical composition of the texture ice, which allows defining individual phases of terrace sedimentation derived from solifluctional downhill movement of sediment. The ice-rich cryostructure results from repeated cycles of thawing and freezing within the soil moisture of the active layers. Stable oxygen isotope signatures and composition of light soluble anions and cations within supernatant texture ice shows prominent relative maxima and minima. They are associated with more humid and more arid phases during the terrace formation. Heavy mineral composition shows a constant uphill source area, the predominance of a silt-sized sediment matrix and single grain surface textures reveal tracks of cryogenic weathering. Second, an ice wedge formation contained in the terrace deposits has been sampled. It allows distinguishing a wide-meshed polygonal growth in the bottom part from a more close-meshed polygonal growth to the top. The upper generation of close-meshed polygons is associated with more arid conditions of a modern cold continental climate, a fact resembling the results from frozen sediment studies. Stable oxygen and deuterium isotope composition documents a Holocene age for the ice wedge growth. It suggests an epigenetic origin of the wedge ice within older sediments and it confirms that the wedge ice inhibits a stable isotope signal for winter precipitation, whereas the surrounding texture ice within the frozen sediments contains a mixture of winter and summer precipitations. Finally, a conclusive sedimentation model is given. It illustrates solifluctional terrace formation during interstadial time at a continental permafrost site.
DE: 9315 Arctic region
DE: 5462 Polar regions
DE: 1823 Frozen ground
DE: 1040 Isotopic composition/chemistry
DE: 1625 Geomorphology and weathering (1824, 1886)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting