New insights on young black carbon in pelagic Atlantic sediments

Black carbon (BC) is ubiquitous in pelagic sediments and presumed to have an older radiocarbon age due to long ocean residence times and pre-aging in terrestrial soils. Here, we applied a multi-method approach to identify different BC fractions in sediments from five regions in the subtropical Atlantic Ocean. Soot-like BC composed between 15±6% of the sedimentary organic carbon in the Northwest Argentina basin and 54±20% in the Amazon Delta. Black carbon sediment accumulation rates were six times greater in the Sierra Leone Rise (6 mg cm^-2 kyr^-1) than in the remote South Atlantic (0.9 mg cm^-2 kyr^-1), possibly due to enhanced regional atmospheric deposition. Radiocarbon years for soot-like BC from subtropical Atlantic sediments were more modern compared to the bulk total organic carbon, and were apportioned as biomass burning byproducts from their stable carbon isotopic signatures. This study demonstrated that the subtropical Atlantic Ocean sediment serves as an important sink for young BC.