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Fluxes of Soot Carbon to South Atlantic Sediments
Citation:
Lohmann, R., K. Bollinger, M. G. CANTWELL, J. Feichter, I. Fischer-Burns, AND M. Zabel. Fluxes of Soot Carbon to South Atlantic Sediments. Global Biogeochemical Cycles. American Geophysical Union, Washington, DC, 23:1-13, (2009).
Impact/Purpose:
To construct a global mass balance of black carbon
Description:
Deep sea sediment samples from the South Atlantic Ocean were analyzed for soot black carbon (BC), total organic carbon (TOC), stable carbon isotope ratios (δ 13C), and polycyclic aromatic hydrocarbons (PAHs). Soot BC was present at low concentrations (0.04–0.17% dry weight), but accounted for 3–35% of TOC. Fluxes of soot BC were calculated on the basis of known sedimentation rates and ranged from 0.5 to 7.8 μg cm−2 a−1, with higher fluxes near Africa compared to South America. Values of δ 13C indicated a marine origin for the organic carbon but terrestrial sources for the soot BC. PAH ratios implied a pyrogenic origin for most samples and possibly a predominance of traffic emissions over wood burning off the African coast. A coupled ocean-atmosphere-aerosol-climate model was used to determine fluxes of BC from 1860 to 2000 to the South Atlantic. Model simulation and measurements both yielded higher soot BC fluxes off the African coast and lower fluxes off the South American coast; however, measured sedimentary soot BC fluxes exceeded simulated values by ∼1 μg cm−2 a−1 on average (within a factor of 2–4). For the sediments off the African coast, soot BC delivery from the Congo River could possibly explain the higher flux rates, but no elevated soot BC fluxes were detected in the Amazon River basin. In total, fluxes of soot BC to the South Atlantic were ∼480–700 Gg a−1 in deep sea sediments. Our results suggest that attempts to construct a global mass balance of BC should include estimates of the atmospheric deposition of BC.