Collaborative Research: Dissolved Organic Matter Degradation in Filtering Shelf Sands

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Knowledge of the sizes and turnover times of discrete pools of carbon is essential for accurate accounting and modeling of global ocean carbon dynamics. Production or sink terms of the oceanic pool of dissolved organic carbon (DOM), one of the largest exchangeable carbon reservoirs on earth, can strongly impact the balance between oceanic and atmospheric CO2 or change the storage of carbon in marine deposits. The continental shelf acts as sink for large quantities of DOM that reach the sea through rivers and runoff from land. Although a large fraction of the terrigenous DOM is refractory, it does not accumulate in the shelf and oceans, a process that is not well understood but is critical for the global cycles of carbon. In this research, PIs from Florida State University and University of North Carolina at Chapel Hill hypothesize that DOM laden coastal water is pumped through the surface layers of permeable shelf sediments by bottom currents and waves, forcing DOM through a biocatalytical converter with large reactive surface area and different biogeochemical reaction zones. Their prior NSF funded investigations showed an average 200-fold increase in enzymatic hydrolysis rates between sediments and water column. The specific objectives of the proposed research are 1) quantification of DOM degradation in filtering Gulf of Mexico sands and overlying water 2) assessment of the influences of pore flow velocity, temperature, oxygen concentration and light on DOM decomposition rates, 3) FT-ICR-MS characterization of DOM compositional changes caused by sediment passage and 4) quantification of the abundance of metabolically active prokaryotes and establishment of a direct linkage between DOM metabolism and the phylogenetic composition of microbial communities, 5) integration of the results into an empirical model that quantitatively relates DOM degradation rates to pore water velocity, temperature, oxygen and light. The broader impacts include development of a project web site, public lectures, news releases to the public media and information materials distributed to visitors of the FSU marine lab located at the study site. Human resource development will be enhanced through active participation of undergraduate students in field and laboratory research, and four graduate students will develop their theses based on aspects of this research. The project will enhance international visibility and collaboration through active participation of researchers from Germany, the Netherlands, and Panama.