Abstract. The Siberian Arctic Sea shelf and slope is a key region for the degradation
of terrestrial organic material transported from the organic-carbon-rich
permafrost regions of Siberia. We report on sediment carbon mineralization
rates based on O2 microelectrode profiling; intact sediment core
incubations; 35S-sulfate tracer experiments; pore-water dissolved
inorganic carbon (DIC); δ13CDIC; and iron, manganese, and
ammonium concentrations from 20 shelf and slope stations. This data set
provides a spatial overview of sediment carbon mineralization rates and
pathways over large parts of the outer Laptev and East Siberian Arctic shelf
and slope and allows us to assess degradation rates and efficiency of carbon
burial in these sediments. Rates of oxygen uptake and iron and manganese
reduction were comparable to temperate shelf and slope environments, but
bacterial sulfate reduction rates were comparatively low. In the topmost 50 cm of sediment, aerobic carbon mineralization dominated degradation and
comprised on average 84 % of the depth-integrated carbon mineralization.
Oxygen uptake rates and anaerobic carbon mineralization rates were higher in
the eastern East Siberian Sea shelf compared to the Laptev Sea shelf.
DIC ∕ NH4+ ratios in pore waters and the stable carbon isotope
composition of remineralized DIC indicated that the degraded organic matter
on the Siberian shelf and slope was a mixture of marine and terrestrial
organic matter. Based on dual end-member calculations, the terrestrial
organic carbon contribution varied between 32 and 36 %, with a higher
contribution in the Laptev Sea than in the East Siberian Sea. Extrapolation
of the measured degradation rates using isotope end-member apportionment over
the outer shelf of the Laptev and East Siberian seas suggests that about 16 Tg C yr−1 is respired in the outer shelf seafloor sediment. Of the organic
matter buried below the oxygen penetration depth, between 0.6 and 1.3 Tg C yr−1 is degraded by anaerobic processes, with a terrestrial organic
carbon contribution ranging between 0.3 and 0.5 Tg yr−1.
The impact of a thermodynamic sea-ice module in the COSMO numerical weather prediction model on simulations for the Laptev Sea, Siberian Arctic
