Estimate of glacial silicic acid reduction over the last 600 ka in the Bering Sea using delta Si-30 of diatom frustules

摘要

Enhanced ocean stratification during glacial periods is the main factor depressing the biogenic opal productivity in the subarctic North Pacific and its marginal seas. However, there are no quantitative estimations of glacial nutrient reduction despite the importance of the glacial-interglacial nutrient cycle. In this study, delta Si-30 of diatom frustules (delta Si-30(diatom)) was measured in order to provide a record of silicic acid utilization over the last 600 ka at IODP Site U1343. The d30Sidiatom record revealed distinct orbital-scale changes: high delta Si-30(diatom) (i.e., high silicic acid utilization) during the interglacial periods and low delta(30)(Sidiatom) (i.e., low silicic acid utilization) during the glacial periods. These changes are explained by the glacial-interglacial differences of Fe-concentration and sea-ice influence on surface-water productivity. This study estimated the glacial reduction of silicic acid supply and utilization in the Bering slope area. Based on the glacial-interglacial average delta Si-30(diatom) values using the Rayleigh closed model, the glacial silicic acid level was estimated to be >63% of the interglacial level and the glacial silicic acid utilization was significantly lower (<37%) than during interglacial periods (similar to 64%).