Dissolution of biogenic silica in Southern Ocean surface sediments

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.