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Biogeochemistry of organic matter and associated elements along the river-estuary-ocean continuum
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Ocean mixing and the removal of marine refractory dissolved organic carbon
Tuesday 8th @ 1450-1510, Conference Hall
Yuan Shen* , Ocean Sciences Department, University of California, Santa Cruz, California, USA 95064
School of the Earth, Ocean and Environment, University of South Carolina, Columbia, South Carolina, USA 29208
Ronald Benner, School of the Earth, Ocean and Environment, University of South Carolina, Columbia, South Carolina, USA 29208
Presenter Email: yshen56@ucsc.edu |
| A large quantity of reduced carbon is sequestered in the ocean as refractory dissolved organic carbon (DOC) that persists through several circuits of global overturning circulation. Key aspects of the fate and removal of refractory DOC remain an enigma after decades of research. Herein we investigate mechanisms that remove refractory DOC using bioassay experiments with DOC isolated from surface, mesopelagic and deep waters of the Atlantic Ocean. The isolated DOC was refractory to degradation by native microbial communities, even at elevated concentrations. However, when the refractory DOC was introduced to a series of novel environmental conditions, including addition of labile substrate, microbial inocula from coastal waters and exposure to solar radiation, a substantial fraction (7-13%) was removed within 1.5 years. Our results suggest that while refractory molecules can persist in the ocean for millennia, removal is rapid when they encounter their fate. The observed and projected climate-induced slowdown of global overturning circulation could reduce the exposure of refractory molecules to disparate removal processes. Assuming a constant rate of production, the reservoir size of refractory DOC could increase as overturning circulation slows, providing a negative feedback to rising atmospheric CO2. |
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