Black carbon concentrations, sources, and fluxes in the tropical Atlantic Ocean

Kari Ann Pohl, University of Rhode Island

Abstract

Black carbon (BC) is the highly graphitized byproduct of incomplete combustion that could be a sink for fixed carbon. Little data is currently available for BC concentrations and fluxes to remote marine environments and there are often great discrepancies between model simulations and actual field measurements. This research analyzed BC concentrations in the mixed boundary layer, surface water, and deep pelagic sediments of the Tropical Atlantic Ocean in order to understand the fate and transport of BC to the marine environment. It also aimed to assess the importance of aeolian versus fluvial BC deposition. Black carbon concentrations were elevated in regions directly influenced by fluvial and atmospheric deposition in all environmental matrices compared to regions with minimal terrestrial inputs (such as the Sargasso Sea). Black carbon concentrations and fluxes to deep pelagic sediments were approximately 5 times greater in the Sierra Leone Rise (within an atmospheric emission plume) than the remote South Atlantic (minimal terrestrial inputs). Elevated BC fluxes at the Sierra Leone Rise were most likely due to biomass burning from the African continent, as evidence by biomarkers, enriched stable carbon isotopes, and a modern radiocarbon age. Atmospheric deposition composed 4-28% of the soot-like BC and at least 43% of the total BC in the fluvial region of the Niger Delta, suggesting that atmospheric BC deposition to remote sediments can be significant in areas with elevated biomass burning. Atmospheric BC concentrations were also enhanced within the African biomass burning emission plume. Charcoal composed up to 66% of the BC, suggesting that measurements which only quantify soot-like BC forms may be underestimating this carbonaceous fraction. Additionally, surface mixed layer BC was found to compose an average of 17% of bulk total organic carbon. This implies that terrigenous organic carbon composes a larger fraction of the pelagic organic pool than previously estimated. Overall, BC was detected in all samples regardless of environmental matrix, demonstrating its stability and persistence in the marine environment. Fluvial deposition appeared to be the greatest transport mechanism of BC to the marine environment; however atmospheric transport is quantitatively important and should be included in mass balance estimates of both black carbon and terrigenous organic carbon, especially in areas with significant inputs of biomass burning.^

Subject Area

Chemical Oceanography|Environmental Health

Recommended Citation

Kari Ann Pohl, "Black carbon concentrations, sources, and fluxes in the tropical Atlantic Ocean" (2014). Dissertations and Master's Theses (Campus Access). Paper AAI3628659.
http://digitalcommons.uri.edu/dissertations/AAI3628659

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