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Late Quaternary landscape dynamics of nonglaciated Arctic Siberia Results from eight years of studying the Laptev Sea coastal lowlands

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Schirrmeister, L. , Hubberten, H. W. , Andreev, A. , Grosse, G. , Kienast, F. , Meyer, H. , Siegert, C. , Schwamborn, G. , Kunitsky, V. , Kuznetsova, T. , Derevyagin, A. Y. and Kuzmina, S. (2006): Late Quaternary landscape dynamics of nonglaciated Arctic Siberia Results from eight years of studying the Laptev Sea coastal lowlands , Workshop: Correlation of Pleistocene Events in the Russian North (COPERN) St. Petersburg, December 4-6 .
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Abstract:

Numerous coastal exposures and drill cores of permafrost deposits have been studied in the coastal lowlands surrounding the Laptev Sea to the East Siberian Sea since 1998 within the frame of the Russian-German Science Cooperation SYSTEM LAPTEV SEA. Geochronological, palaeoecological, sedimentological, and geocryological studies permit the reconstruction of palaeoenvironment dynamics of these nonglaciated Arctic lowlands in Yakutia. Permafrost aggradation and degradation, triggered by Quaternary climate changes, are the most important regional processes characterizing the landscape evolution. Composite sequences are presented illustrating the various palaeoenvironmental stages within the last 200,000 years. Both, sharp sedimentary discontinuities probably caused by seismotectonic events, and long-term, gradual transitions in accumulation conditions were discovered. In addition, there are clear differences in local stratigraphy between the eastern part of the Laptev Sea region (New Siberian Islands and the Dimitrii Laptev Strait) and the western Laptev Sea area (Lena Delta; Lena-Anabar lowland).The presentation will summarize our new palaeoenvironmental results and stratigraphic conclusions starting from Late Saalian (Tazovsky) Ice Complex deposits on Bolshoy Lyakhovsky Island, the reconstruction of records from Eemian (Kazantsevo) ice wedge casts, and Early Weichselian (Zyryansky) floodplain deposits there. In the western Laptev Sea region, the visible permafrost sequences started later beginning with Early Weichselian (Zyryansky) fluvial deposits that reflect extended fluvial runoff in front of the main mountain chains (the Kharaulakh, the Chekanovsky and the Pronchshishev Ridges) between 100 to 60 ky BP.The onset of the widely distributed Yedoma sequences varies between 80 and 28 ky BP at various locations. Nevertheless, there were generally similar accumulation conditions for these ice-rich permafrost deposits with huge ice wedge growth in flat and poorly drained lowland plains. Whereas Yedoma sequences are evident only until 28 ky on New Siberian Islands other sequences (e.g. at Bykovsky Peninsula) cover a period until the end of the Late Pleistocene. Despite the ongoing discussion about Karginsky Interstadial (ca 50 - 25 ky BP) records in Siberia there is clear evidence for environmental variations during this period in the studied area. Even if the MIS 3 interstadial period in northern Yakutia was not developed as strong as in other regions the terrestrial arctic palaeo records mirrors to the global trend of climate changes between two glacial periods.In addition new data from sandy deposits of the Arga Complex in the western Lena Delta prove the simultaneous accumulation of Yedoma and fluvial deposits in front of the Chekanovsky Ridge.The strongest environmental impact at the Laptev Sea margins is caused by extended permafrost degradation in response to the Holocene warming and the simultaneous sea level rise. It has resulted in the formation of numerous thermokarst depressions, the flooding of the shelf plain, and in a general reorganisation of the hydrological regime. The formation of thermokarst depressions seem to have started probably earlier on the New Siberian Islands than in the western Laptev Sea region. The regional Holocene Thermal Optimum is documented in paleoecological records at about 9 - 7 ky BP.

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