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Abstract. The Siberian Arctic Sea shelf and slope is a key region for the degradationof terrestrial organic material transported from the organic-carbon-richpermafrost regions of Siberia. We report on sediment carbon mineralizationrates based on O 2 microelectrode profiling; intact sediment coreincubations; 35 S-sulfate tracer experiments; pore-water dissolvedinorganic carbon (DIC); δ13 C DIC ; and iron, manganese, andammonium concentrations from 20 shelf and slope stations. This data setprovides a spatial overview of sediment carbon mineralization rates andpathways over large parts of the outer Laptev and East Siberian Arctic shelfand slope and allows us to assess degradation rates and efficiency of carbonburial in these sediments. Rates of oxygen uptake and iron and manganesereduction were comparable to temperate shelf and slope environments, butbacterial sulfate reduction rates were comparatively low. In the topmost 50 cm of sediment, aerobic carbon mineralization dominated degradation andcomprised on average 84 % of the depth-integrated carbon mineralization.Oxygen uptake rates and anaerobic carbon mineralization rates were higher inthe eastern East Siberian Sea shelf compared to the Laptev Sea shelf.DIC  ∕  NH 4 + ratios in pore waters and the stable carbon isotopecomposition of remineralized DIC indicated that the degraded organic matteron the Siberian shelf and slope was a mixture of marine and terrestrialorganic matter. Based on dual end-member calculations, the terrestrialorganic carbon contribution varied between 32 and 36 %, with a highercontribution in the Laptev Sea than in the East Siberian Sea. Extrapolationof the measured degradation rates using isotope end-member apportionment overthe 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 organicmatter buried below the oxygen penetration depth, between 0.6 and 1.3 Tg C yr −1 is degraded by anaerobic processes, with a terrestrial organiccarbon contribution ranging between 0.3 and 0.5 Tg yr −1 .

Carbon mineralization in Laptev and East Siberian sea shelf and slope sediment