Description: Sediment redistribution at the seafloor is a widespread process in marine environments. In the last years, increasing evidence has been found that sedimentary budgets for biogenic silica and other components may be strongly biased by sediment focusing. The natural radioisotope Thorium-230 provides a method for correcting fluxes into the sediment for this lateral transport. The 230Th-normalization method has so far been applied to individual sediment cores and some longitudinal sectionsonly, giving a first impression of the strong influence of sediment redistribution. However, the database of 230Th-corrected data had been too scarce to calculate reliable spatial budgets for whole ocean basins. Here we present a comprehensive set (114 samples) of 230Th-corrected biogenic silica accumulation rate data for surface sediments in the South Atlantic and adjoining areas. The focusing-corrected budgets for silica are considerably lower than earlier estimates.The focusing-corrected accumulation rates, representing vertical fluxes intothe sediment, will facilitate the comparison of core data to model results.

Description: Biogenic silica (BSi) is a major component in marine geochemical cycles and a suitable proxy for paleoproductivity. The Southern Ocean plays a key role in the biogeochemical cycle of silicon. For questions of opal preservation and to assess the global biogenic silica cycle it is important to understand the processes controlling BSi dissolution.The results from fitting the leaching curves, derived by wet-alkaline-extraction of biogenic silica, gives an estimate of the reactivity of biogenic silica in sediments. To get detailed information on kinetics and solubility of biogenic silica, continuously stirred flow-through experiments were performed. Use of flow through reactors allow quantification of dissolution rates and saturation concentrations under well defined conditions. Dissolution rates of sediment samples in stirred flow-through reactors were measured as a function of the degree of undersaturation by varying the silica acid concentrations or the flow rate of the inflow solution. By taking samples out of the reactors during the experiments we also get information about changes in species composition and how the shell structures dissolve. Sediment samples were selected from different regions of the Southern Ocean, e.g. Weddel Sea, Scotia Sea, Polar Front Zone.The information about BSi dissolution kinetics will be considered in a regional context. For this purpose detailed information of diatom assemblages and clay mineralogy are considered. The combination of results from laboratory measurements and regional distribution of parameters affecting the benthic silica cycle helps us decipher processes regulating the BSi burial and provides a more detailed understanding of the dissolution of BSi in surface sediments within certain regions of the Southern Ocean.

Description: Submarine groundwater discharge was observed for different sedimentologicalsettings of coastal areas around the world. In several regions discharge of fluids from the seabed is associated with formation of pockmarks or other morphological features at the seafloor. Since sampling of fluids and sediments at e.g., pockmarks is rathercomplicate, the understanding of the flow field and the spatial distribution of chemical components around discharge sites is rather limited.Studies in the Wadden Sea of the Weser estuary showed that significant areas are affected by discharge of freshwater from below. In several cases high flow ratescause formation of "sand boils". Based on pore water studies and flow measurements discharge rates and chemical composition (e.g., nutrients, CH4) were determined. Flow rates of several liter per hour were observed. Small scale sampling allowed the determination of the flow field at the discharge sites. A budget for the release of nutrients for this part of the Wadden Sea is provided.