NON-STEADY STATE PROCESSES AND OTHER EFFECTS ON CARBON AND SULFUR BURIAL IN AN ESTUARY (Invited Presentation)

Estuaries can be major sinks in the biogeochemical carbon and sulfur cycles. Much of our framework for evaluating the processes that affect rates of organic carbon and sulfur burial in sediments comes from steady-state, one-dimensional models of sediment diagenesis. Yet many estuaries are highly-dynamic, with seasonal changes in primary productivity, bioturbation, and rates of microbially-mediated reactions that consume products of the degradation of organic matter. These types of seasonal variability can challenge the assumptions of steady-state, one-dimensional models. We present carbon and sulfur isotope data from two nearby (~4 km apart) sites in the Chesapeake Bay – one in the deep channel that experiences a longer duration of seasonal bottom water anoxia and one on the shelf that is more frequently ventilated with oxygen. We show how a non-steady state process – a spring diatom bloom – has minimal impacts on organic carbon burial. However, it does impact pathways of oxidation of the sulfide that is produced by the degradation of organic matter by sulfate reducing microorganisms. Using sulfur and carbon isotope geochemistry along with information about microorganisms carrying out sulfide oxidation, we examine the range of processes that contribute to higher carbon and sulfur concentrations in the shelf site that experiences more frequent ventilation than the deeper site with a longer duration of summer anoxia. The results show that processes that contribute to high rates of organic carbon and sulfur burial may actually be promoted in sites with more frequent ventilation compared to those with more persistent anoxia.