Effect on the Chemical and Isotopic Composition of Marine Dissolved Organic Matter by Adsorption to Deep Sea Sediment.

Refractory marine dissolved organic carbon (DOC) is the ocean’s largest respired carbon pool and has an average radiocarbon age of 4900 to 6500 14C years. Yet, the inputs to and outputs from this pool are poorly constrained. Marine sediments may provide an important source of refractory DOC by the conversion of sinking labile particulate organic carbon into more recalcitrant structures. In this study, we examine how adsorption to marine sediments alters the chemical composition and radiocarbon age of DOC. Artificial and natural sediments were cleaned and incubated with organic matter standards. Water extractable DOC was collected by centrifugation and filtration and analyzed for radiocarbon content and molecular composition by nuclear magnetic resonance and mass spectrometry. In particular, we examined these data for evidence of preferential adsorption of either radiocarbon-enriched or radiocarbon-depleted molecules and the preferential adsorption of either labile or recalcitrant molecules. In this presentation, we will discuss the findings from these experiments. We anticipate that these results will provide insight towards the role of sediments in pre-aging DOC or converting labile DOC into refractory DOC. This, in turn, will provide a more complete picture of the elusive nature of refractory DOC.