Spatial Heterogeneity of Terrestrial Organic Carbon Burial and Degradation in the East Siberian Arctic Shelf Area

Abstract

Climate warming has led to the translocation of a large amount of terrestrial organic carbon (TerrOC) into the Arctic Ocean. The fate of TerrOC varies dramatically in the Arctic shelves, thus introducing uncertainty into the climate-carbon feedback. In this study, we analyzed total organic carbon (TOC), stable organic carbon isotopes (δ13C) and lignin to investigate the spatial heterogeneity of sources and degradation of sedimentary OC on the East Siberian Arctic Shelf (ESAS). Furthermore, we also compared the cross-shelf degradation of TerrOC between the ESAS and Beaufort Shelf. High lignin content (0.51–2.25 mg/100 mg OC) and relatively depleted δ13C (−27.47‰ to −25.72‰) indicate that sedimentary OC in the nearshore areas of Laptev Sea and East Siberian Sea is predominantly of terrestrial origin, while in the rest area of the ESAS, the contribution of marine OC plays a dominant role in the OC burial. The distribution results of OC loadings and degradation proxy (3,5-Bd/V) suggest that OC supply is the main factor controlling the nearshore distribution of OC loadings. The simultaneous decrease of OC loadings (from 1.44 to 0.15 mg/m2) and increase of 3,5-Bd/V (from 0.04 to 0.73) indicate that TerrOC degradation could be an important mechanism controlling the offshore decrease of OC. Compared to the broad ESAS, although the inherent characteristics of the TerrOC sources could not be ignored, the inconspicuous variations in lignin content and degradation proxy in the narrow Beaufort Shelf may indicate that the shelf width could be an important factor influencing the offshore degradation of TerrOC.