Brüchert, V., Bröder, L., Sawicka, J. E., Tesi, T., Joye, S. P., Sun, X., Semiletov, I. P., and Samarkin, V. A., 2018. Carbon mineralization in Laptev and East Siberian sea shelf and slope sediment. Biogeosciences: 15, 471.

The Siberian Arctic Sea shelf and slope is a key re- gion for the degradation of terrestrial organic material trans- ported from the organic-carbon-rich permafrost regions of Siberia. We report on sediment carbon mineralization rates based on O 2 microelectrode profiling; intact sediment core incubations; 35 S-sulfate tracer experiments; pore-water dis- solved inorganic carbon (DIC); δ 13 C DIC ; and iron, man- ganese, 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 effi- ciency 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 sul- fate 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 east- ern East Siberian Sea shelf compared to the Laptev Sea shelf. DIC / NH + 4 ratios in pore waters and the stable carbon iso- tope composition of remineralized DIC indicated that the de- graded 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 con- tribution in the Laptev Sea than in the East Siberian Sea. Ex- trapolation 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 be- tween 0.3 and 0.5 Tg yr − 1 .

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