Presenter: Niels Hauksson (University of California, Irvine)

Description:
Rivers discharge significant quantities of terrigenous dissolved organic carbon (DOC) to the ocean. Though the magnitude of this input would be sufficient to explain the turnover time of DOC in the ocean, biomarker and isotope studies suggest that unaltered terrigenous DOC comprises a small amount of total marine DOC. Much of the removal or alteration of terrigenous DOC is believed to occur in the coasts and at estuaries. The chemical selectivity of these processes may explain the small terrigenous signal in the ocean DOC. In this study, we assess how marine sediment affects the solubility and isotopic composition of Suwanee River normal organic matter (2R101N), a riverine DOC standard collected by the International Humic Substances Society. The standard was incubated with marine sediment in a 35‰ NaCl solution, and then separated into solid and dissolved phases by centrifugation and filtration. The mass of organic carbon, d¹³C, and ∆¹⁴C were measured for both phases. As sediment to terrestrial organic matter ratios increased, we found that d¹³C  and ∆¹⁴C of the DOC increased and decreased respectively. This indicates that the sediment captured components of the DOC that have lower d¹³C  and higher ∆¹⁴C than the bulk.  This work has implications for understanding the mismatch between carbon export measurements and carbon isotopes of riverine DOC in the open ocean.