Keywords:intermediate water, Cycladophora davisiana, Bering Sea
Radiolarians are marine zooplankton with biogenic opal skeleton living in surface to deep ocean. Radiolarian microfossil assemblages in deep-sea sediments are used as paleoceanographic indicators and stratigraphic markers. Cycladophora davisiana is a radiolarian species dwelling in intermediate water with low temperature, high oxygen concentration, and rich in organic carbon. Therefore, increase and decrease in C. davisiana abundance in marine sediments suggests the presence of ventilated intermediate water. The Bering Sea, a marginal sea located in the North Pacific, is to be a source region of well-ventilated intermediate water in the glacial North Pacific. Here we show changes of C. davisiana abundances in sediment core obtained from the Kamchatka Strait, the largest strait in the Bering Sea, to reconstruct intermediate water formation change since last glaciation. KST-2A piston core sample was obtained from the Kamchatka Strait during Mu18 cruise by R/V Prof. Multanovskiy (56°11’N;165°1’E; water depth 3545 m; core long 454 cm). KST-2A-PC recorded past 20 kyrs (since the last glacial maximum, LGM) based on radiocarbon dating of planktic foraminifera and calcium concentration patterns. Two types of microslides were prepared for light microscopic observation by sieved through screens with different mesh opening sizes (>63 μm and >45 μm). Total radiolarian abundances (No. skeleton g-1) have gradually increased for the past 20 kyrs. Cycladophora davisiana abundances (No. skeleton g-1) fluctuated with peaks during deglacial warming periods. Although the total radiolarian and C. davisiana abundances (No. skeleton g-1) were significantly low during LGM, relative abundances (%) of C. davisiana were high during LGM as well as the deglacial warming periods. These C. davisiana abundance patterns suggest that intermediate water formation was active in the Bering Sea during the deglaciation. Total radiolarian abundances (No. skeleton g-1) estimated by using >45 μm were much higher than those of >63 μm. However, there was no significant difference in %C. davisiana patterns between >45 μm and >63 μm samples.