Coastal permafrost landscape development in the northern Yukon – East Beringia vs. Laurentide Ice –

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Fritz, M. , Wetterich, S. , Schirrmeister, L. , Meyer, H. , Lantuit, H. and Pollard, W. H. (2012): Coastal permafrost landscape development in the northern Yukon – East Beringia vs. Laurentide Ice – , From Knowledge to Action. IPY 2012 Conference, Montreal, Canada, 22 April 2012 - 27 April 2012 .
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The Yukon Coastal Plain (YCP) facing the Southern Beaufort Sea was only partly glaciated during the last glacial maximum (LGM). Large areas remained ice-free and became part of the vast unglaciated land mass − Beringia − and is therefore an excellent study area to reconstruct paleoenvironmental dynamics where records since the late Pleistocene are still sparse. Multi-proxy analyses on permafrost deposits and stable water isotopes on ground ice (buried glacier ice, ice wedges, pore ice) have been applied to unravel periglacial processes towards sedimentary history, permafrost aggradation and degradation through time as well as to link these processes to distinct periods of climatic change. Ice-thrust sets up to 180 m above sea level have incorporated remnants of Laurentide ice, which today become exposed due to coastal erosion. Deglaciation of the ice-cored ridge along the YCP was accompanied by alluvial and eolian sediment supply to the easternmost fringe of Beringia until ~11 cal ka BP during a period of low glacio-eustatic sea level. Strongly negative δ18O values of late Wisconsinan ice wedges indicate colder-than-modern winter temperatures and probably reduced snow depths. Beyond the glacial limit, basal dates on peat and ice-wedge cast deposits suggest that until 11.4 cal ka BP bioproductivity was inhibited due to continuous harsh climate conditions. The late glacial–Holocene transition was marked by higher-than-modern temperatures that led to permafrost degradation beginning no later than 11.2 cal ka BP and caused a regional thaw unconformity. Thaw lakes developed as a result of extensive thermokarst. Rapid accumulation of peat followed on wet polygonal ground. Thermokarst evolved into ice-wedge casts and started to fill with lacustrine deposits, which were subsequently covered by rapidly accumulating peat during the Holocene Thermal Maximum. A rising permafrost table, reduced peat accumulation, and extensive ice-wedge growth resulted from climate cooling starting in the middle Holocene. The reconstruction of paleo-landscape dynamics on the YCP and in east Beringia may contribute to unraveling the cross-linkages and feedback mechanisms between ice sheet, ocean, and permafrost since the late Wisconsin.

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