[M-IS16] Paleoclimatology and paleoceanography

[MIS16-15] Reconstruction of Early Pleistocene sea-surface temperature in the Northwestern Pacific Ocean based on calcareous microfossils

*Daisuke Kuwano¹, Yuki Tsuchiya², Yuma Oura¹, Hiroki Hayashi³, Yoshimi Kubota⁴, Kanako Mantoku⁵, Koji Kameo¹ (1.Chiba University, 2.Nagoya University, 3.Shimane University, 4.National Museum of Nature and Science, 5.National Institute for Environmental Studies)

Keywords:Calcareous nannofossils, Planktonic foraminifera, Modern Analog Technique, Paleoceanography, Pleistocene, Kazusa Group

Planktonic foraminifera and calcareous nannofossils have been used to clarify past marine environments based on relationships between distributions of living taxa and sea-water conditions (e.g., Takemoto and Oda, 1997; Aizawa et al., 2004). In this study, we reconstruct the sea surface temperature (SST) based on the Modern Analog Technique (MAT) of calcareous microfossil assemblages. The MAT is a useful method for reconstructing SST by comparing the similarity between fossil and modern assemblages (e.g., Pflaumann et al., 1996). Around the Pacific coast of Japanese islands, many surface sediments have been obtained by grab sampler and piston corer, and the modern microfossil assemblages of those have been studied (e.g., Tanaka, 1991). We apply the MAT to 27 samples of the upper part of the Kiwada Formation, Kazusa Group, obtained by Kuwano et al. (in press). We estimated the SST by calculating the squared chord distance (SCD) between fossil and modern assemblages, subsequently taking the weighted temperature average of the top five samples with the highest similarity. The modern foraminiferal and nannofossil assemblage dataset were obtained from Takemoto and Oda (1997) and Tanaka (1991), respectively. The modern SST dataset was used in July from the Japan Oceanographic Data Center (2004).
The reconstructed SST tends to be high during interglacial, and the summer SST ranged between 23.4 and 27.7 ℃. On the other hand, during the glacial Marine Isotope Stage (MIS) 38, the SSTs temporarily dropped by 1–2 ℃. This sea-surface variation is similar to that of planktonic foraminiferal δ¹⁸O change although the nannofossil SSTs were sharp declines rather than planktonic δ¹⁸O changes in some horizons.

[Reference]
Aizawa et al., 2004, Marine Micropaleontology, 52, 277–297.
Japan Oceanographic Data Center, 2004, https://jdoss1.jodc.go.jp/vpage/bts_j.html
Kuwano et al., in press, Stratigraphy.
Pflaumann et al., 1996, Paleoceanography, 11, 15–35.
Takemoto and Oda, 1997, Paleontological research, 1, 291–310.
Tanaka, 1991, Sci. Rep., Tohoku Univ., 2nd ser. (Geol.), 61, 127-198.