11:30 〜 11:45
[MIS03-09] Towards quantitative reconstruction of past Kuroshio variability: Initial results of Cruise KS-22-4
キーワード：東シナ海、酸素同位体、有孔虫
The Kuroshio western boundary current transports heat and moisture poleward. Variations in its strength affect both global and regional climate, yet our understanding of long-term Kuroshio variability remains poor, particularly prior to the current interglacial. To reconstruct past Kuroshio variability, five piston cores were recovered from the eastern and western edges of the central Okinawa Trough during cruise KS-22-4 of the Shinsei Maru. The sites are located along depth transects with the goal of obtaining information from similar paleowater depths on each side of the trough. Quantitative bottom water temperature records will then allow us to reconstruct the isothermal gradients through time to assess how the strength of the current has varied in the past.
Extensive radiocarbon dating has been performed on four of the five sites using shell material sampled during core description and the planktic foraminifer Neogloboquadrina. dutertrei picked from the top of every core section and the bottom of each core. Results indicate that the recovered cores range in age from modern to ~50 ka. Sediment accumulation rates tend to decrease during deglaciation on both sides of the trough, perhaps due to a decrease in sediment supply associated with rising sea level and reflooding of the Taiwan Strait. Planktic foraminifer oxygen isotope ratios obtained from the deepest site (~900 mbsl; PC02) on the western edge of the trough record millennial-scale events during the last glaciation and deglaciation. Bottom water temperature on the eastern edge of the trough at a relatively shallow site (~300 mbsl; PC03) was stable during the past 12 ka, with little increase during the Holocene. We estimate that this site experienced ~60 m sea level rise. Based on World Ocean Atlas data for the site, an increase in depth of 60 m corresponds roughly to a 2ºC temperature decrease. Thus, the Holocene warming was likely offset by the rising sea level.
Extensive radiocarbon dating has been performed on four of the five sites using shell material sampled during core description and the planktic foraminifer Neogloboquadrina. dutertrei picked from the top of every core section and the bottom of each core. Results indicate that the recovered cores range in age from modern to ~50 ka. Sediment accumulation rates tend to decrease during deglaciation on both sides of the trough, perhaps due to a decrease in sediment supply associated with rising sea level and reflooding of the Taiwan Strait. Planktic foraminifer oxygen isotope ratios obtained from the deepest site (~900 mbsl; PC02) on the western edge of the trough record millennial-scale events during the last glaciation and deglaciation. Bottom water temperature on the eastern edge of the trough at a relatively shallow site (~300 mbsl; PC03) was stable during the past 12 ka, with little increase during the Holocene. We estimate that this site experienced ~60 m sea level rise. Based on World Ocean Atlas data for the site, an increase in depth of 60 m corresponds roughly to a 2ºC temperature decrease. Thus, the Holocene warming was likely offset by the rising sea level.