[M-IS14] Paleoclimatology and paleoceanography

[MIS14-15] Change in deep-seawater [CO₃^2-] in the Southern Pacific during the last interglacial

★Invited Papers

*Shinya Iwasaki¹, Katsunori Kimoto², Lester Lembke-Jene³, Rika Horiuchi², Kana Nagashima², Frank Lamy³, Julia Rieke Hagemann³, Helge Arz⁴, Takuto Kasuya⁵, Kota Sakaoka¹, Tomohisa Irino¹, Naomi Harada⁶ (1.Graduate School of Environmental Science, Hokkaido University, 2.JAMSTEC, 3.AWI, 4.Leibniz Institute for Baltic Sea Research, 5.Kyushu University, 6.University of Tokyo)

Keywords:Planktonic foraminifera, carbonate dissolution, X-ray CT scan, ocean carbon cycle, Glacial and interglacial

Deep seawater upwells to the surface in the Pacific Southern Ocean, exchanges carbon with the atmosphere, and then sinks back into the deep ocean. Such a deep seawater circulation system significantly impacts the atmospheric CO₂ concentration. It has been suggested that carbon was released from this ocean area to the atmosphere, increasing the atmospheric CO₂ concentration during the last deglaciation (approx. 19–12 Ka). On the other hand, from the previous interglacial to the last glacial maximum (approx. 130 – 20 ka), the atmospheric CO₂ concentration gradually decreased, and the amount of carbon should have been stored in the deep ocean. However, the process and the amount of carbon stored in the deep ocean are poorly understood. In this study, the dissolution intensity of planktonic foraminiferal shells in the sediment cores, collected from five sites at different water depths between 1000 to 4000 m, was measured using X-ray micro-CT scanning to reconstruct the variations in deep seawater carbonate ion concentration in the Pacific Southern Ocean. The results show that a pronounced event of carbonate dissolution was identified in 80 ka at the site deeper than 3000 m, which indicates a decrease in carbonate ion concentration of 20 µmol kg^-1. Focusing on longer-tern variations, on the other hand, deep seawater carbonate ion concentration was higher during glacial and lower during interglacial periods, suggesting that the carbon-rich water masses may have been located at shallower water depth during the glacial periods.