Diatom records in the Quaternary marine sequences around the Japanese Islands

The main aim is to provide the results of Td'-SSTs (°C) based on the late Pliocene to Pleistocene sequences from three holes obtained by deep-sea drilling (DSDP-ODP). The main difference between Td' and Twt is that Twt gives 0.5 values to Xt (warm transitional taxa). Thalassiosira oestrupii is grouped with Xt in Twt but with warm-water species in Td'. Differences between the Twt and Td'-SSTs (°C) curves at Hole 436 are unremarkable. The remarkable variations of paleo-temperatures based on Td'-SSTs (°C) show four conspicuous episodes which correspond to the double precession cycle of MIS 11. In the Japan Sea, the Twt ratio remarkably decreases at 2.6 Ma due to a large increase in cold-water taxa, and indicates the beginning of the glacial age defined as the Pliocene/Pleistocene boundary. Both Twt and Td'-SSTs (°C) increase at 2.60-2.0 Ma, and coincide with the lithologic change from diatom-bearing clay with few dark-colored layers to fine-grained sediments with distinct dark-light colored cycles. Wavelet analysis of Td'-SSTs (C) at Site 798 indicates a reversed saw-tooth pattern of 48 to 24-ky periods during 1.2-0.7 Ma, and 24 to 12-ky periods during 0.7-0 Ma, resulting in a change from longer to shorter cycles. These fluctuations correlate with the Earth's orbital parameters and climatic changes on a millennial time scale.