Estuarine cycling of carbonyl sulfide: production and sea–air flux

A 3 year field and laboratory study of estuarine carbonyl sulfide (OCS) was undertaken during 1991–1994 to more accurately quantify the variability of coastal OCS fluxes and to investigate mechanisms that lead to elevated OCS concentrations in coastal waters. Results from the water column of the Chesapeake Bay show no definitive seasonal trends in the sea–air flux of OCS, although these fluxes are over 50 times more than those from the open ocean. In contrast, fluxes of OCS from estuarine sediments were found to be highest in the summer, and contribute up to 75% of the total sources of OCS in this estuary. Laboratory incubations of Chesapeake Bay sediments using different carbon substrates, inhibitors, and temperature show that OCS production is coupled to microbial sulfate reduction. These results explain the high sediment porewater concentrations and high sediment–water fluxes in the summer, and combined with the field data, provide evidence that anoxic sediments can be an important component of the OCS budget in coastal waters.