09:45 〜 10:00
[U13-04] Ultra-high resolution oxygen isotope records from the Chiba Composite Section ratified as the Chibanian GSSP
★Invited Papers
キーワード：チバニアン、前期－中期更新世境界、酸素同位体比、黒潮続流前線、海洋酸素同位体ステージ１９
Marine isotope stage (MIS) 19 has been suggested as one of the best orbital analogs for present interglacial, because of the similarity of the orbital configurations between both interglacial periods. Therefore, paleoenvironmental reconstructions of MIS 19 will provide valuable knowledge to evaluate the anthropogenic impacts for present and future climate changes. The Chiba composite section (CbCS) in the Boso Peninsula, central Japan, is a marine succession straddling the Early–Middle Pleistocene boundary, ranges from the late MIS 20 to early MIS 18. The Chiba section, a main portion of the CbCS, has been ratified as the Global Boundary Stratotype Section and Point (GSSP) of the Chibanian Stage/Age by the Executive Committiee of the International Union of Geological Science on January 17, 2020 (Suganuma et al., 2021). The subtropical Kuroshio and subpolar Oyashio currents generate the large latitudinal water temperature gradient off the Boso Peninsula, and strongly influence the East Asian climate. Therefore, the CbCS sensitively documents a behavior of the Kuroshio Current across the Early–Middle Pleistocene boundary. In this study, we reconstructed detailed oxygen isotope (δ18O) records using surface and subsurface planktonic, and benthic foraminifera from the CbCS to reveal paleoceanographic variation in the northwestern Pacific from the late MIS 20 to early MIS 18.
The age model of the CbCS was established by correlating the benthic δ18O record to the sea level curve obtained from the southwestern Pacific (Elderfield et al., 2012). The resultant age interval of the δ18O records is 747.6–801.1 ka on average temporal resolution of 160 yr with a chronological uncertainty of 5 kyr. MIS 19 (MIS 19a, 19b, and 19c) substages are assigned based on climatic variability proposed by Nomade et al. (2019). Vertical water temperature structure and their gradient (ΔT) exhibit latitudinal displacements of the Kuroshio Extension Front (KEF) on multi-millennial scale across the MIS 20–19 transition and during late MIS 19 (MIS 19b to 19a). Results of the spectral and wavelet analyses for the δ18O records show periodicities of approximately 3,000–6,000 year from MIS 19b to 19a. Similarities of timing and periodicity between paleoceanographic records from the CbCS, North Atlantic, and Mediterranean indicate that disruption of the Atlantic meridional overturning circulation due to freshwater discharge into the North Atlantic caused the southward displacements of the KEF via atmospheric dynamic.
The age model of the CbCS was established by correlating the benthic δ18O record to the sea level curve obtained from the southwestern Pacific (Elderfield et al., 2012). The resultant age interval of the δ18O records is 747.6–801.1 ka on average temporal resolution of 160 yr with a chronological uncertainty of 5 kyr. MIS 19 (MIS 19a, 19b, and 19c) substages are assigned based on climatic variability proposed by Nomade et al. (2019). Vertical water temperature structure and their gradient (ΔT) exhibit latitudinal displacements of the Kuroshio Extension Front (KEF) on multi-millennial scale across the MIS 20–19 transition and during late MIS 19 (MIS 19b to 19a). Results of the spectral and wavelet analyses for the δ18O records show periodicities of approximately 3,000–6,000 year from MIS 19b to 19a. Similarities of timing and periodicity between paleoceanographic records from the CbCS, North Atlantic, and Mediterranean indicate that disruption of the Atlantic meridional overturning circulation due to freshwater discharge into the North Atlantic caused the southward displacements of the KEF via atmospheric dynamic.