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Quartz weathering in freeze-thaw cycles; experiment and application as a permafrost tracer to Elgygytgyn sedimentary records

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Schwamborn, G. , Fedorov, G. , Diekmann, B. , Schirrmeister, L. and Hubberten, H. W. (2010): Quartz weathering in freeze-thaw cycles; experiment and application as a permafrost tracer to Elgygytgyn sedimentary records , IODP/ICDP Kolloquium, 09. - 11.03.2010, Frankfurt a. M. .
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Abstract:

Brittle and fragile sand and silt is produced in Siberian near surface permafrost. It makes up much of the regolith in permafrost areas such as Arctic Siberia. Microscopical grain features (e.g. angular outlines, surficial microcracks) stem from cryogenic destruction in the course of numerous seasonal freezing and thawing events in the uppermost soil. Even after a grain is transported off place (i.e. in mobile slope material, in seasonal melt-water run-off, into a lake basin), it still keeps the particular weathering traces in their single grain micromorphology.This is also valid for a mineralogical peculiarity; frost weathering is a selective grain break-up. In contrast to lower latitudes, quartz is more sensitive to weathering in high latitudes. Quartz quickly reacts to cryogenic break-up and small grains disintegrate due to the explosive power of expanding ice in micro-meter scale fissures. This quartz enrichment in the fines also evolves from seasonal freeze-thaw (F/T) weathering and the grain break-up is demonstrated in an experimental set-up where >100 F/T cycles preferentially crack quartz grains (with reference to feldspar). Minerogenic debris in the upper 12 core meters from Elgygytgyn Crater lake, which is placed north of the Arctic circle in NE Russia, is characterised by silt abundance, cryogenic grain micromorphology, and quartz enrichment in the silt fraction. This argues for persistent permafrost conditions in the area back to 220.000 years as reflected by the continuous input of cryogenic weathering detritus into the basin. Even when periods were as warm as or warmer than today (i.e. during the Eemian Interglacial) the permafrost signal does not disappear

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