The Microbial Carbon Pump and Bacterial Carbon Sequestration in the Ocean

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The Biological Pump has long been recognized as an important sink for atmospheric CO2 concentrations through the sequestration of carbon in ocean sediments. The contributions of bacteria to the sequestration of carbon in the ocean reservoir of refractory dissolved organic carbon (RDOC) have only recently been recognized. This process, conceptualized as the Microbial Carbon Pump (MCP), also appears to play a significant role in carbon sequestration and the regulation of atmospheric CO2. In this project, researchers at the University of South Carolina at Columbia will build upon the framework of the MCP to address the following hypotheses: 1) The production and composition of bacterial DOC vary with biological (e.g. community structure) and physicochemical (e.g. nutrients) parameters in the ocean, 2) Bacteria sequester carbon in semi-labile DOC (SDOC) that persists for years to decades in mesopelagic waters, 3) Microbial communities in mesopelagic and bathypelagic waters have the metabolic potential to produce and degrade bacterial DOC. Naturally-occurring bacterial DOC in these waters is very resistant to microbial degradation, 4) Heterotrophic bacteria are the predominant source of bacterial SDOC and RDOC. These hypotheses will be addressed using a combination of field (NW Pacific Ocean and Sargasso Sea) and experimental approaches to investigate spatial variability in the production and decomposition of bacterial DOC and to relate these processes to community structure and environmental conditions. This study will provide estimates of the reservoirs of bacterial SDOC and RDOC in the ocean and critical insights about the ocean carbon cycle and the regulation of atmospheric CO2 concentrations. It will also lay a foundation for addressing how the MCP and bacterial carbon sequestration will respond to climate change. Broader Impacts: This project will strengthen collaborations between the PI's laboratory and Dr. Hiroshi Ogawa's laboratory at the Atmosphere and Ocean Research Institute in Japan. This collaboration includes participation on a Japanese-sponsored expedition to the North Pacific Ocean aboard the R/V Hakuro maru. Additionally, it will support a postdoctoral associate and a doctoral student who will participate on research expeditions to the NW Pacific Ocean and Sargasso Sea. Their research will focus on the MCP, and they will present their findings at national conferences in years 2 and 3.