Characterization of in-situ organic matter degradation in three regime types of collapsing Arctic Ice Complex Deposits on the SE Laptev Sea coast.

L. Sánchez-García, J. Vonk, A. Charkin, D. Kosmach, O. Dudarev, I. Semiletov, Ö. Gustafsson (2014).

Arctic amplification of climate warming is intensifying the thaw and coastal erosion of the widespread and
carbon-rich Siberian Ice Complex Deposits (ICD). Despite the potential for altering long-term carbon dynamics
in the Arctic, the susceptibility of organic carbon (OC) to degradation as the ICD thaw is poorly characterised.
This study identifies signs of OC degradation in three Siberian ICD regimes of coastal erosion through elemental,
isotopic and molecular analyses. The degree of erosion appears to determine the extent of degradation. The
moisture-limited and beach-protected ICD bluff near Buor-Khaya Cape, characterised by thermokarst mounds
(baydzherakhs), represents a dormant regime with limited ongoing degradation. Conversely, the more exposed
ICD scarps on eroding riverbanks (Olenek Channel, Lena Delta) and coastal slopes (Muostakh Island) showed
more pronounced signs of ongoing OC decay. Different parameters suggest that degradation can partially explain
the shift of the OC signature with 14C age in the thawing ICD. Exposure time, degree of erosion, slope
gradient and moisture conditions appear to be key factors determining the degradation propensity of OC in exposed
ICD. These field results document the lability of OC in ICD upon thaw and illustrate the potential for
transferring old OC into the rapidly cycling atmosphere-biosphere carbon pools.

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