Late Quaternary accretion and decline of syngenetic ice-rich permafrost

• Main Authors: Wetterich, Sebastian, Strauss, Jens, Fuchs, Margret C., Schirrmeister, Lutz
• Format: Conference Object
• Language: unknown
• Published: COPERNICUS GESELLSCHAFT MBH 2016
• Subjects: Ice; permafrost; Thermokarst; Tundra; wedge*
• Online Access: https://epic.awi.de/id/eprint/41975/; https://epic.awi.de/id/eprint/41975/1/WetterichEGU2016-12840.pdf; https://hdl.handle.net/10013/epic.48777; https://hdl.handle.net/10013/epic.48777.d001

The region of perennially frozen ground constitutes one quarter of the northern hemisphere landmass. Negative annual mean air temperatures and ground freezing periods exceeding ground thaw periods are the prerequisites for downward freezing of loose deposits and bedrock in non-glaciated regions. Hence, permafrost distribution and thickness on Earth are closely related to late Quaternary climate variations and ecosystem modifications. Generally, glacial stages are expected to promote permafrost accretion and ground ice formation in accumulating sediments,whereas interglacial stages lead to intense permafrost thaw and ground-ice melt. Deep freezing synchronous with ongoing sedimentation is termed as syngenetic while epigenetic freezing occurs in pre-existing deposits. Typical landforms of syngenetic permafrost are ice-wedge polygons of past tundra environments. Ice-rich silty and/or peaty deposits intersected by large ice wedges (up to several decameters in height and meters in with) build-up unique Ice Complex (IC) strata, which are aligned to mid- and late Pleistocene stadial and interstadial stages. The most prominent example for such formations is the Yedoma IC of MIS 3 interstadial age. Increasing air and ground temperatures during warm stages disturbed the thermal equilibrium at the upper permafrost boundary and subsequently led to permafrost thaw, ground-ice melt and surface subsidence. Typical permafrost degradation processes are thermokarst and thermo-erosion that result in large lake-filled basins (up to kilometers in diameter) and valley structures, respectively. The modern periglacial surface in Alaskan and East Siberian lowlands preserves Yedoma IC remnants in uplands and hills next to widely-distributed thermokarst basins since lateglacial and Holocene warming affected up to 70% of the original IC distribution on an area of more than 1,000,000 km2. The overarching climate-driven pattern of cold-stage IC permafrost accretion and warm-stage IC permafrost degradation provides, however, only a ...