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Late Quaternary sedimentation history of a coastal permafrost landscape, Western Laptev Sea, NE Siberia

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Winterfeld, M. , Schirrmeister, L. , Overduin, P. P. , Grigoriev, M. and Kunitsky, V. (2010): Late Quaternary sedimentation history of a coastal permafrost landscape, Western Laptev Sea, NE Siberia , Proceedings, Third European Conference on Permafrost, Longyearbyen, Svalbard, NorwayJune 2010. .
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Abstract:

Palaeoenvironmental reconstructions of the land-scape history of the western Laptev Sea are primar-ily based on studies of exposed cliffs and surface sediment cores. During the COAST drilling cam-paign in April 2005 a transect of deeper cores was drilled at Cape Mamontov Klyk in the western Lap-tev Sea. Here, we present the reconstruction of a coastal permafrost landscape including periods of permafrost aggradation and degradation and reach-ing back to at least the Eemian interglacial based on cryolithological, sedimentological, geochronological (14C-AMS, OSL on quartz, IR-OSL on feldspars), and palaeoecological (pollen, diatoms) analyses.The study area is located in the western Laptev Sea at the coastal cliff of Cape Mamontov Klyk (73.61°N, 117.18°E). The investigated borehole transect reached up to ~12 km offshore including 5 cores, one terrestrial (C1) and four marine cores (C2 to C5) at different distances from the coast. The most distant core (C2) reached the maximum depth of 77 m below sea level (b.s.l.). The lowermost unit I (figure 1) was only observed in core C2 (77 to 64.7m b.s.l.) and mainly consisted of silty sands with several clayey layers. The largely plastic-cryotic state (i.e. ice-bearing but not ice-bonded) was a result of pore water salinities of 11.7 to 30.8 depressing the freezing point, combined with temperatures of -1.0 to -1.4°C at these depths. Along with pollen data, pore water isotope values and one IR-OSL age of 111±7.5 ka ( at 77 m b.s.l.) a marine interglacial (Eemian) origin seems to be pos-sible although the depth b.s.l. was unexpected, par-ticularly when compared to marine Eemian deposits on the Taymyr Peninsula identified up to 100 m above sea level (a.s.l.). The subsequent landscape development was primarily governed by sea level changes. Aggradation of terrestrial permafrost (unit II + III) on the shelf occurred during the Weichselian glaciation and the Holocene (unit IVa). The unfro-zen, cryotic (<0°C) sediment unit IVb was a result of modern coastal erosion of unit III and IVa sediments and their re-deposition in the marine environment as well as thermal and chemical degradation of unit II from above.Figure 1. Proposed lithostratigraphical units representing dif-ferent stages of landscape development. The distances between single cores are not to scale.New marine sedimentological evidence adds to ex-isting terrestrial records from exposures and surface sediments, showing strong late Quaternary land-scape dynamics and coastal development in the western Laptev at least back to the Eemian. On-shore, terrestrial sediments were encountered down to 50 m b.s.l.; offshore, marine sediments lie deeper than 65 m b.s.l. beneath relict terrestrial permafrost. These results focus our line of questioning regarding the relative sea level, glacio-isostatic and neotec-tonic history of the region.

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