The Black Carbon Cycle: Budget and Fluxes of Black Carbon in South Atlantic Sediments

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).In this study, researchers at the University of Rhode Island will attempt to determine the origin and fluxes of black carbon (BC) in marine sediments from the South Atlantic. Black carbon in the atmosphere is a key driver of global climate change; it is second only to CO2 in its contribution to global warming. The proposed work is thus relevant and timely for our understanding of the carbon cycle, a key component of our ability to forecast climate and its change. The major sources of BC on the global scale are fossil fuel and biomass burning, which are both prominent in Africa and South America. Hence, it is proposed to account for soot BC, char and charcoal residing in sediments from the South Atlantic by combining thermal, chemical and petrographic isolation methods.This project has three main hypotheses: (1) Soot BC constitutes a significant fraction of the total organic carbon in deep sea sediments of the South Atlantic, and dominates total BC in those sediments; (2) Biomass burning is the dominant source of the soot BC present in deep sea sediments of the South Atlantic; and (3) For the South Atlantic, atmospheric deposition of soot BC is as important as riverine inputs.This study represents a first attempt to account for BC sinks on an Ocean scale. It thus holds promise to make a major step forward towards being able to mass balance sources and sinks of BC. Previous studies suggest that BC reaches the oceans predominantly from riverine sources. In the case of the South Atlantic, the research team hypothesizes that atmospheric transport and deposition is at least as important. The proposed research will compare different BC determination procedures for deep sea sediments, thereby improving our understanding of the different constituents of the BC cycle. Similarly, organic marker molecules are often used for source apportionment. This study will explore if this still holds true for deep sea sediment samples, as preliminary data found discrepancies arising from molecular marker analysis and isotopic analysis. Lastly, accounting for soot BC in deep sea sediments will also aid in identifying more of the uncharacterized sedimentary OC . Broader Impacts: The results of this work are expected to aid atmospheric and earth system science modelers in refining their atmospheric and oceanic transport models for BC, including its relation to global climate change. The project will enhance infrastructure for research and education by establishing research collaboration between URI and international partners at the University of Bremen, the MPI for Meteorology, Hamburg, and the University of Tuebingen.