Paleoenvironmental analysis from fossil ostracod assemblages of the Middle Pleistocene Naganuma Formation in the Sagami Group, central Japan

Abstract A high-resolution radiolarian record from 800 to 750 ka was examined from the Chiba composite section (CbCS) of the Kokumoto Formation, including the GSSP (Global Boundary Stratotype Section and Point) for the Lower–Middle Pleistocene boundary, on the Boso Peninsula, Pacific side of central Japan. Total radiolarian abundance was closely related to biological productivity in the sea-surface layer and was observed to increase and repeatedly decrease in the millennial-scale period. Summer SST (sea-surface temperature), which was estimated based on the radiolarian assemblage, was 19°C at the end of MIS-20 (790-793 ka) and fluctuated between 21 and 26°C during MIS-19, with the warm periods tending to be synchronous with high productivity. Recent observations have revealed that productivity increases with a northward shift of the Kuroshio along the Kuroshio-Oyashio boundary zone. Therefore, high productivity in the warmer and stratified conditions during MIS-19 can be interpreted as being closely related to millennial-scale oscillations of the Kuroshio Extension. Such millennial-scale climatic changes were also recognized in southern Europe and are likely related to shifts in climate systems such as AO (Arctic Oscillations).

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Millennial-scale changes in sea-surface temperature and productivity along the Kuroshio–Oyashio boundary during MIS-19 based on the radiolarian record from the Chiba composite section, central Japan

10.21203/rs.3.rs-24663/v1 ◽

2020 ◽

Author(s):

Takuya Itaki ◽

Sakura Utsuki ◽

Yuki Haneda ◽

Kentaro Izumi ◽

Yoshimi Kubota ◽

...

Keyword(s):

Surface Temperature ◽

Sea Surface Temperature ◽

Sea Surface ◽

Middle Pleistocene ◽

Central Japan ◽

High Productivity ◽

Pacific Side ◽

Composite Section ◽

The Kuroshio ◽

Millennial Scale

Abstract A high-resolution radiolarian record from 800 to 750 ka was examined from the Chiba composite section (CbCS) of the Kokumoto Formation, including the GSSP (Global Boundary Stratotype Section and Point) for the Lower–Middle Pleistocene boundary, on the Boso Peninsula, Pacific side of central Japan. Total radiolarian abundance was closely related to biological productivity in the surface layer and was observed to increase and repeatedly decrease in the millennial-scale period. Summer SST (sea-surface temperature), which was estimated based on the radiolarian assemblage, was 19°C at the end of MIS-20 (790-793 ka) and fluctuated between 21 and 26°C during MIS-19, with the warm periods tending to be synchronous with high productivity. Recent observations have revealed that productivity increases with a northward shift of the Kuroshio along the Kuroshio-Oyashio boundary zone. Therefore, high productivity in the warmer and stratified conditions during MIS-19 can be interpreted as being closely related to millennial-scale oscillations of the Kuroshio Extension. Such millennial-scale climatic changes were also recognized in southern Europe and are likely related to shifts in climate systems such as AO (Arctic Oscillations) and PDO (Pacific Decadal Oscillations).

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