Spatial pattern of BSi-Dissolution-Index in the Southern Ocean

Biogenic silica (BSi) is a major component in marine geochemical cycles and a suitableproxy for paleoproductivity. The Southern Ocean plays a key role in the biogeochemicalcycle of silicon. To understand opal preservation mechanisms and to assessthe global biogenic silica cycle it is important to study the processes controlling BSidissolution kinetics. Common techniques for the assessment of dissolution kineticsare flow-through and batch experiments. In this study, information on BSi dissolutionkinetics will be considered in a regional context. For this purpose about 60 samplesfrom the Atlantic sector of the Southern Ocean were investigated. To identify spatialpatterns of a BSi-Dissolution-Index, the result from fitting the leaching curves, derivedby wet-alkaline-extraction of biogenic silica, gives an estimate of the reactivityof biogenic silica in sediments. To get detailed information on kinetics and solubilityof biogenic silica, continuously stirred flow-through experiments were performed.Use of flow through reactors allows quantification of dissolution rates and saturationconcentrations under well defined conditions. Dissolution rates of sediment samplesin stirred flow-through reactors were measured as a function of the degree of undersaturationby varying the silica acid concentrations or the flow rate of the inflow solution.Sediment samples were selected from different regions of the Southern Ocean, e.g.Weddel Sea, Scotia Sea, Polar Front Zone. The results of the BSi dissolution kineticsand detailed information on diatom assemblages and clay mineralogy are considered.The combination of results from laboratory measurements and regional distribution ofparameters affecting the benthic silica cycle can be used to decipher processes regulatingthe BSi burial. In addition a more detailed understanding of the dissolution of BSi in surface sediments within certain regions of the Southern Ocean can be provided.