Dissolved organic carbon (DOC) in Arctic ground ice, from northwest Canada, east Siberia, and Alaska

Thermal permafrost degradation and coastal erosion in the Arctic remobilize substantial amounts of organic carbon (OC) and nutrients which have accumulated in late Pleistocene and Holocene unconsolidated deposits. Permafrost vulnerability to thaw subsidence, collapsing coastlines and irreversible landscape change are largely due to the presence of large amounts of massive ground ice such as ice wedges. However, ground ice has not, until now, been considered to be a source of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and other elements which are important for ecosystems and carbon cycling. Here we show, using biogeochemical data from a large number of different ice bodies throughout the Arctic, that ice wedges have the greatest potential for DOC storage, with a maximum of 28.6 mg/L (mean: 9.6 mg/L). Variation in DOC concentration is positively correlated with and explained by the concentrations and relative amounts of typically terrestrial cations such as Mg2+ and K+. DOC sequestration into ground ice was more effective during the late Pleistocene than during the Holocene, which can be explained by rapid sediment and OC accumulation, the prevalence of more easily degradable vegetation and immediate incorporation into permafrost. We assume that pristine snowmelt is able to leach considerable amounts of well-preserved and highly bioavailable DOC as well as other elements from surface sediments, which are rapidly frozen and stored in ground ice, especially in ice wedges, even before further degradation. We found that ice wedges in the Yedoma region represent a significant DOC (45.2 Tg) and DIC (33.6 Tg) pool in permafrost areas and a freshwater reservoir of 4200 km**3. This study underlines the need to discriminate between particulate OC and DOC to assess the availability and vulnerability of the permafrost carbon pool for ecosystems and climate feedback upon mobilization.

Concentrations of organic compounds in suspended matter from surface waters and surface layer bottom sediments of the Obskay Guba (Ob River estuary) and the Kara Sea

Data are presented on concentrations of aliphatic and polycyclic aromatic hydrocarbons (AHC and PAH) in interstitial waters and bottom sediments of the Kara Sea compared to distribution of particulate matter and organic carbon. It was found that AHC concentrations within the water mass (aver. 16 µg/l) are mainly formed by natural processes. Distribution of AHC represents variability of hydrological and sedimentation processes in different regions of the sea. The widest ranges of the concentrations occurred in the Obskaya Guba - Kara Sea section: in water (10-310 µg/l for AHC and 0.4-7.2 ng/l for PAH) and in the surface layer of the bottom sediments (8-42 µg/l for AHC and 9-94 ng/g for PAH). Differentiation of hydrocarbons (HC) in different media follows regularities typical for marginal filters; therefore no oil and pyrogenic compounds are supplied to the open sea. In sediments contents of HC depend on variations in redox conditions in sediments and on their composition.