Isotopic composition of oceanic dissolved black carbon reveals non-riverine source

Sasha Wagner, Rensselaer Polytechnic Institute, Earth and Environmental Sciences, Troy, NY, United States, Jay Brandes, University of Georgia, Skidaway Institute of Oceanography, Department of Marine Sciences, Savannah, GA, United States, Robert G Spencer, Florida State University, Department of Earth, Ocean and Atmospheric Science, Tallahassee, FL, United States, Kun Ma, University of Georgia, Skidaway Institute of Oceanography, Savannah, United States, Sarah Rosengard, University of British Columbia, Vancouver, BC, Canada, Jose Mauro Sousa Moura, Federal University of Western Pará, Programa de Pós Graduação em Recursos Naturais da Amazônia, Santarem, Brazil and Aron Stubbins, Northeastern University, Chemistry and Chemical Biology, Boston, United States
Abstract:
A portion of the charcoal and soot produced during combustion processes on land (e.g., wildfire, burning of fossil fuels) enters aquatic systems as dissolved black carbon (DBC). In terms of mass flux, rivers are the main identified source of DBC to the oceans. Since DBC is believed to be representative of the refractory carbon pool, constraining sources of marine DBC is key to understanding the long-term persistence of carbon in our global oceans. Here, we use compound-specific stable carbon isotopes (δ13C) to reveal that DBC in the oceans is ~6‰ enriched in 13C compared to DBC exported by global rivers. This isotopic discrepancy suggests most riverine DBC is sequestered and/or rapidly degraded before it reaches the open ocean. Thus, we suggest that oceanic DBC does not predominantly originate from rivers and instead may be derived from another pool of black carbon with an isotopic signature similar to that of a marine phytoplanktonic source.
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