Spatiotemporal Variations and Sources of Black Carbon in Surface Sediments and Sinking Particles in the Western Arctic Ocean

Abstract To investigate the migration and transformation of black carbon (BC) under rapid Arctic changes, we systematically quantified its abundance, distribution and particulate (PBC) flux in the Chukchi Shelf and Borderland, western Arctic Ocean. The average sedimentary BC concentration was 1.29 mg g −1 , with spatial distributions controlled primarily by distance from the coast, water column stratification, and seafloor bathymetry. In the Chukchi Borderland, the mean PBC sinking fluxes reached 0.40 mg m −2 d −1 , exhibiting pronounced seasonal variability, with fluxes during the melting season quadrupling those observed during periods of ice formation. Stable carbon isotopic signatures (δ 13 C BC ) revealed a tripartite BC source mixture throughout the study area: modern biomass combustion, pyrogenic fossil fuel combustion, and petrogenic (coastal erosion) inputs. Finally, we estimated annual BC fluxes of 61 and 655 Gg in the Chukchi Borderland and Central Arctic Ocean, respectively. These findings establish BC as an essential component of the Arctic carbon sink.