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

Abstract

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 O 2 microelectrode profiling; intact sediment core incubations; 35 S-sulfate tracer experiments; pore-water dissolved inorganic carbon (DIC); δ 13 C DIC ; 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 depthintegrated 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 / NH + 4 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 .

Quantifying Degradative Loss of Terrigenous Organic Carbon in Surface Sediments Across the Laptev and East Siberian Sea

“…One reasons why these emissions are so poorly constrained is the fact that lateral carbon fluxes and the role of spatially and temporally displaced feedbacks are currently not properly represented in most estimates (Schuur et al, 2015;Vonk & Gustafsson, 2013), an aspect we are trying to partially alleviate with the current study. Sedimentary terrOC degradation below the mixing layer by anaerobic degradation is low (<20% of the depth-integrated bulk carbon mineralization according to Brüchert et al, 2018, which is consistent with downcore profiles of terrOC and biomarker concentrations in Bröder, Tesi, Salvadó, et al, 2016). Sedimentary terrOC degradation below the mixing layer by anaerobic degradation is low (<20% of the depth-integrated bulk carbon mineralization according to Brüchert et al, 2018, which is consistent with downcore profiles of terrOC and biomarker concentrations in Bröder, Tesi, Salvadó, et al, 2016).…”

“…This difference may in part be due to less oxygen availability in the sediments. Since the oxygen penetration depths for LS + ESS sediments is on the order of a few millimeters (Boetius & Damm, 1998;Brüchert et al, 2018), the average oxygen exposure time for the mixed layer (~4 cm) is much lower than the sedimentary cross-shelf transport time. POC and DOC in oxygenated waters, in contrast, are exposed to oxygen at all times.…”

“…Admittedly, our approach is not accounting for the degradation of terrOC in resuspended sediment/bottom floc occurring at the water-sediment interface, which have been observed indirectly by, for example, Semiletov et al (2016). Sedimentary terrOC degradation below the mixing layer by anaerobic degradation is low (<20% of the depth-integrated bulk carbon mineralization according to Brüchert et al, 2018, which is consistent with downcore profiles of terrOC and biomarker concentrations in Bröder, Tesi, Salvadó, et al, 2016). Therefore, deposition of terrOC in the sediments may function as a removal mechanism for permafrost-released OC from the contemporary carbon cycle.…”

Assessing the potential for non-turbulent methane escape from the East Siberian Arctic Shelf

“…To evaluate the performance of the BRNS set-up in capturing the main diagenetic patterns observed in Arctic shelf sediments we run the model for two case study sites in the area of interest: (1) a site offshore Kotelny Island in the central region of the Laptev Sea, north of the Lena River delta (76.171 • N, 129.333 • E, 56 m water depth) collected during the SWERUS-C3 expedition in summer 2014 (Brüchert et al, 2018;Brüchert, 2020). Although observations are merely available for the first 22 cm, the first 3 m of sediment are simulated to allow for the full development of the early diagenetic network, thus also accounting for biogeochemical processes (e.g.…”

Dissolved Organic Matter at the Fluvial-Marine Transition in the Laptev Sea Using in situ Data and Ocean Color Remote Sensing

“…In offshore resuspension areas with very high TSM concentration, DOC and TSM do not necessarily co-vary. Large amounts of terrigenous organic matter can be mineralized on short time scales (about 50 % within a year, Kaiser et al, (2017)) and strongly degraded when deposited in sediments (Bröder et al, 2016(Bröder et al, , 2019Brüchert et al, 2018).…”