Biogeochemical controls on carbon and sulfur cycling in Baltic Sea sediments

The Baltic Sea is the largest brackish inland sea in the world. Over the last 100 years, the Baltic Sea has received a large amount of nutrients from surrounding watersheds that has increased the primary production, and eutrophication in the water column. Thus, the seafloor of Baltic Sea has received large amounts of organic matter that lead to the enhancement of gas bearing sediments (H2S, CH4, etc). An important aspect was to study the link between organic carbon delivery into the Baltic Sea floor and S, CH4 and C cycling as function of salinity gradients and sediment accumulation rate. Several outcomes of my study could clarify the biogeochemical controls on C and S cycling in the Baltic Sea: 1) The impact of sediment and organic matter fluxes on methane and sulfur cycling in Himmerfjärden estuary sediments; 2) The role of sulfate penetration depth on carbon preservation and sulfur burial in the sediments of in the Baltic Sea; and 3) The impacts of reactive Fe reactivity on sulfurization of organic matter and oxidative sulfur cycling in Gdansk Basin sediments. In the Baltic Sea, low sulfate penetration, and high rate of sediment accumulation rates, are the master variables that control the biogeochemistry of carbon and sulfur cycling; in particular, they may significantly allow for high organic carbon preservation and eventual methane release into the water column.