Biogenic silica dissolution in Southern Ocean sediments

Biogenic silica (BSi) is a major component in marine geochemical cycles and asuitable proxy for paleoproductivity. The Southern Ocean plays a key role in thebiochemical cycle of silicon. For questions of opal preservation and to assess theglobal biogenic silica cycle it is important to understand the processes controling BSidissolution.Continuously stirred flow-through experiments were used to determine the kineticsand solubility of biogenic silica. Use of flow through reactors allow quantificationof dissolution rates and saturation concentrations under well defined conditions.Dissolution rates of sediment samples in stirred flow-through reactors were measuredas a function of the degree of undersaturation by varying the silica acid concentrationsor the flow rate of the inflow solution. Sediment samples were selected from differentregions of the Southern Ocean, e.g. Weddel Sea, Scotia Sea, Polar Front Zone.New and published information about BSi dissolution kinetics will be considered ina regional context. For this purpose detailed information of diatom assemblages andclay mineralogy are considered. Furthermore an up to date compilation of diffusivesilicic acid fluxes and BSi content in surface sediments is presented. The combinationof results from laboratory measurements and regional distribution of parameterseffecting the benthic silica cycle helps us to decipher processes regulating the BSiburial and provides a more detailed understanding of the dissolution of BSi in surfacesediments within certain regions of the Southern Ocean.