ABSTRACT

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, δ³⁰Si of diatom frustules (δ³⁰Si_diatom) was measured in order to provide a record of silicic acid utilization over the last 600 ka at IODP Site U1343. The δ³⁰Si_diatom record revealed distinct orbital-scale changes: high δ³⁰Si_diatom (i.e., high silicic acid utilization) during the interglacial periods and low δ³⁰Si_diatom (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 δ³⁰Si_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 (~64%).