[B-PT03] バイオミネラリゼーションと古環境プロキシー

[BPT03-P03] Calcification response of the planktic foraminifer during the Paleocene-Eocene thermal maximum

*久保田 好美¹、木元 克典²、山口 龍彦¹、木下 峻一¹、リチャード ノリス³ (1.国立科学博物館、2.海洋研究開発機構、3.カリフォルニア州立大学サンディエゴ校　スクリプス海洋研究所)

キーワード：海洋酸性化、有孔虫、暁新世・始新世境界温暖期、マイクロフォーカスX線CT、石灰化

Ocean acidification repeatedly occurs in geological time. It gives various impacts on marine organisms especially those with carbonate skeletons. Foraminifers are protozoa with calcium carbonate skeletons, living in the water column as plankton and on the seafloor as benthos. Studying fossil foraminifers contributes to understanding biotic responses to ocean acidification.
The Paleocene-Eocene thermal maximum (PETM; ~56 million years ago) is a rapid climatic warming event associated with ocean acidification. At the onset of the PETM, deep-sea benthic foraminifers and ostracodes went extinct and planktic foraminifers and calcareous nannofossils underwent origination.
Here we focus on the change in the shell density of fossil planktic foraminifers through the PETM event to elucidate how the planktic foraminifers adapted to the rapid environmental change. The micro-focus X-ray tomography of the planktic foraminifer Subbotina patagonica allows us to estimate the shell density of a foraminifer specimen, that is the intensity of calcification. The shell densities indicate considerable individual variability. The temporal change in the mean shell density has not coincided with changes in sea-surface pH, suggesting that no linear calcification response to ocean acidification.