Incomplete combustion of biomass is the main source of black carbon (BC) to the global oceans via aeolian and fluvial deposition. Typically, particulate BC is pre aged before reaching ocean sediments, its ultimate sink. Annual burning of crop fields in central Africa provides a large source of BC, that may be transported by winds to the equatorial Atlantic and deposited within the intertropical convergence zone. Here, we assessed whether the transport of BC from biomass burning in western Tropical Africa dominates sedimentary black carbon concentrations in the eastern equatorial Atlantic Ocean. We collected multi cores along a 5˚ N transect of the Atlantic Ocean and isolated black carbon using the chemothermal oxidation at 375 ˚C method. BC concentrations decreased westward across the Equatorial Atlantic, with the highest concentrations (0.717 mg/g) north of the Sierra Leon Rise and lowest (0.296 mg/g) west of the mid Atlantic ridge. Source identification using stable carbon isotopes of BC depicted a westward depletion from C4 plants towards C3 plants or fossil fuel dominated values (-17.36 ‰ to -21.02 ‰). The age of surface sedimentary BC in the eastern equatorial Atlantic was younger than the Total Organic Carbon (TOC) (BC: 1460 ± 15 yrs. vs. TOC: 2180 ± 20 yrs.). At least in the eastern equatorial Atlantic, BC had a unique signature from C4 plants that is relatively young and likely originating from biomass burning in Africa. This unique isotopic pattern could be used to further the understanding the transport and fate of black carbon’s role in the carbon cycle.

Primary Presenter: Samuel Katz, University of Rhode Island (sdkatz@uri.edu)

Authors:

Samuel Katz, University of Rhode Island Graduate School of Oceanography  (sdkatz@uri.edu)

Roger Kelly, University of Rhode Island Graduate School of Oceanography  (rokelly@uri.edu)

Rebecca Robinson, University of Rhode Island Graduate School of Oceanography  (rebecca_r@uri.edu)

Rainer Lohmann, University of Rhode Island Graduate School of Oceanography  (rlohmann@uri.edu)