Provenance of Aerosol Black Carbon over Northeast Indian Ocean and South China Sea and Implications for Oceanic Black Carbon Cycling

Aerosol black carbon (BC) influencesclimate forcing. Applyingthe state-of-the-art of dual-carbon isotope technology, we identifiedsix isotope provinces of aerosol BC over a substantial oceanic region,each with distinct BC sources. Aerosol black carbon (BC) is a short-lived climate pollutant.Thepoorly constrained provenance of tropical marine aerosol BC hindersthe mechanistic understanding of extreme climate events and oceaniccarbon cycling. Here, we collected PM2.5 samples duringresearch cruise NORC2016-10 through South China Sea (SCS) and NortheastIndian Ocean (NEIO) and measured the dual-carbon isotope compositions(& delta;C-13-& UDelta; C-14)of BC using hydrogen pyrolysis technique. Aerosol BC exhibits sixdifferent & delta;C-13-& UDelta; C-14 isotopic spaces (i.e., isotope provinces). Liquid fossil fuel combustion,from shipping emissions and adjacent land, is the predominant sourceof BC over isotope provinces "SCS close to Chinese Mainland"(53.5%), "Malacca Strait" (53.4%), and "OpenNEIO" (40.7%). C-3 biomass burning is the major contributorto BC over isotope provinces "NEIO close to Southeast Asia"(55.8%), "Open NEIO" (41.3%), and "Open SCS"(40.0%). Coal combustion and C-4 biomass burning show highercontributions to BC over "Sunda Strait" and "OpenSCS" than the others. Overall, NEIO near the Bay of Bengal,Malacca Strait, and north SCS are three hot spots of fossil fuel-derivedBC; the first two areas are also hot spots of biomass-derived BC.The comparable & delta;C-13-& UDelta; C-14 between BC in aerosol and dissolved BC in surface seawatermay suggest atmospheric BC deposition as a potential source of oceanicdissolved BC.