Sarkar, SiddharthaSiddharthaSarkarRahman, AbdurAbdurRahmanKhan, Mohammad AtifMohammad AtifKhanRathi, AjayetaAjayetaRathiRagavan, P.P.RagavanSingh, ArvindArvindSinghKumar, SanjeevSanjeevKumar2025-08-312025-08-312024-05-1610.1029/2023GL1060502-s2.0-85192083910https://d8.irins.org/handle/IITG2025/28914Black carbon (BC) has emerged as an integral part of the global carbon (C) cycle, constituting 12% ± 5% of the organic C pool in rivers and soils, with the potential to generate negative climate feedback. However, its ability to sequester C depends on the recalcitrant nature of BC in the environment, which is under debate. Using CTO-375 method and by measuring concentrations and isotopic compositions of particulate BC (δ¹³C<inf>PBC</inf>), we explore the transformation of particulate black carbon (PBC) along the atmosphere-river-ocean continuum. Significantly high δ¹³C<inf>PBC</inf> in the ocean compared to rivers and atmospheric particulate matter indicates (a) degradation of PBC, potentially through photodegradation and leaching, and/or (b) availability of an enriched source other than fluvial or aeolian inputs. This evidence for degradation of PBC in aquatic systems warrants rethinking on its C sequestration potential and role in aquatic C biogeochemistry and further raises concerns regarding the use of sedimentary BC as a paleoenvironmental proxy.trueblack carbon | degradation | estuary | ocean | river | stable isotopesArticlehttps://doi.org/10.1029/2023gl1060501944800716 May 20245e2023GL106050arJournal6