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New insights on black carbon in pelagic Atlantic sediments
Citation:
St. Laurent, K., M. Cantwell, AND R. Lohmann. New insights on black carbon in pelagic Atlantic sediments. MARINE CHEMISTRY. Elsevier Science Ltd, New York, NY, , 1-22, (2023). https://doi.org/10.1016/j.marchem.2023.104312
Impact/Purpose:
A better understanding of black carbon concentrations, source, and transport is driven by its implications in climate forcing, its role as a human health hazard and its potential to be a sink for fixed carbon when deposited to remote regions. This study demonstrated that the subtropical Atlantic Ocean serves as an important sink for the burial of young carbon presumably from biomass burning. Black carbon in Subtropical Atlantic sediments composed substantial fractions (15-54%) of the bulk sedimentary organic carbon, revealing that terrestrial organic material exists in large quantities in this remote region. Based on stable isotope analysis, our results imply that a substantial fraction of sedimentary carbon in the tropical Atlantic was of terrestrial origin rather than from in situ marine productivity. Lastly, the younger black carbon age compared to the total organic carbon suggests the black carbon in the Atlantic Ocean has a different origin and transport time than in the Pacific Ocean and that fossil carbon input is currently minor.
Description:
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 analyzed sediments from five regions in the subtropical Atlantic Ocean to quantify the black carbon fraction of the total organic carbon pool. Black carbon, derived from the chemothermal oxidation method, comprised between 17¿±¿6% of the sedimentary organic carbon in the Northwest Argentina Basin and 65¿±¿18% in the Amazon Delta. Black carbon sediment accumulation rates were six times greater in the Sierra Leone Rise (8.4¿±¿4.1¿mg¿cm−2 kyr−1) compared to the remote Northwest Argentina Basin (1.3¿±¿0.4¿mg¿cm−2 kyr−1), possibly due to enhanced regional atmospheric deposition from annual African grassland fires. The radiocarbon age for BC from subtropical Atlantic sediments were more modern compared to the bulk total organic carbon, and BC source was apportioned as biomass burning byproducts from their stable carbon isotopic signatures and characteristic ratios of polycyclic aromatic hydrocarbons. This study demonstrated that subtropical Atlantic Ocean sediments serve as an important sink for young BC.
