[M-IS18] Paleoclimatology and paleoceanography

[MIS18-17] Early Pleistocene Paleoceanography around the Kuroshio region based on the past sea surface temperature from calcareous nannofossils

*Daisuke Kuwano¹, Soki Hirota¹, Koji Kameo¹, Masayuki Utsunomiya², Makoto Okada³ (1.Chiba University, 2.National Institute of Advanced Industrial Science and Technology, 3.Ibaraki University)

Keywords:Nannofossils, Pleistocene, Kazusa Group, Sea surface temperature

The northwestern Pacific Ocean is characterized by a warm Kuroshio Current and a cold Oyashio Current, and these currents are important to reconstruct the global paleoceanographic change (e.g., Gallagher et al., 2015). The Kuroshio Current meets the Oyashio Current around off Boso Peninsula, and the sea surface temperature (SST) drops significantly from the Kuroshio Current to the Oyashio Current (Locarnini et al., 2013). Therefore, the SST changes obtained from the Kazusa Group in the Boso Peninsula enable us to infer the past hydrographic change in the northwestern Pacific. In this study, the SST was reconstructed based on the Modern Analog Technique (MAT) of calcareous nannofossil assemblages obtained from the Kiwada Formation to the Kokumoto Formation of the Kazusa Group.
The reconstructed SSTs showed cyclic changes, which are interpreted to reflect fluctuations in the Kuroshio Current corresponding to glacial-interglacial cycles. The SSTs in the interglacial between MIS 37 to 19 indicated high temperatures (~26℃) than those during MIS 1 (Yamamoto et al., 2005). In the glacial periods, the SST was 24°C in MIS 32, while 22°C in MIS 20. This difference between MIS 32 and MIS 20 might reflect a global cooling, and future studies are needed to examine more detail from the Otadai to the Umegase Formation, including MIS 32 to MIS 20.

[References]
Gallagher et al., 2015, Progress in Earth and Planetary Science, 2:17.
Locarnini et al., 2013, World Ocean Atlas 2013, Volume 1: Temperature.
Yamamoto et al., 2005, Geophysical Research Letter, 32, 1–4.