Paleoceanographic change off central Japan since the last 144,000 years based on high-resolution oxygen and carbon isotope records

摘要

Very large sea surface temperature (SST) fluctuations are expected in the northwest Pacific Ocean between glacial and interglacial periods due to possible latitudinal migrations of the steep SST front between the Oyashio and Kuroshio Currents. To reconstruct the SST changes for the past 144,000 years, we conducted high-resolution oxygen and carbon isotope analysis of both benthic and planktonic foraminifera from an IMAGES core off central Japan. Using a newly developed method [Oba, T, Murayama, M., 2004. Sea surface temperature and salinity changes in the northwest Pacific since the last glacial maximum. J. Quat. Sci. 19(4), 335-346] for the reconstruction of the SST, we have found very large (～20℃) SST fluctuations, with minimum SSTs of 3-4℃ during Marine Isotope Stage (MIS) 2 and the MIS 6/5e transition, and with peak SSTs of 22-23℃ during early MIS 1 and the MIS 5a/4, 5c/5b and 5e/5d transitions. The SSTs varied in parallel with changing carbon isotope differences between Globorotalia inflata and Globigerina bulloides, which suggests that the SST changes were primarily caused by the latitudinal displacements of the Kuroshio-Oyashio Currents. We have also found that northward shifts of the Kuroshio Current lagged up to several thousand years at these transitions. Strong correlation between the SST shifts and orbital forcing indicates that the latitudinal displacements of the Kuroshio-Oyashio Currents were influenced by summer insolation at 65°N associated with ENSO-like climatic variability in the tropical Pacific.