[M-IS03] Evolution and variability of the Asian Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS03-10] Eccentricity control on the carbonate-organic matter “rain ratio” in the Pleistocene Indo-Pacific warm pool region

*山本 正伸¹ (1.北海道大学大学院地球環境科学研究院)

キーワード：レインレイショ、 炭素循環、円石藻、二酸化炭素

Coccolithophorids are a major carbonate producer in tropical oceans. Their produced carbonate and organic matter are efficiently exported to the deeper oceans, being sometimes assumed to influence global ocean carbon cycles potentially. The morphology of Noelaerhadaceae, dominant coccolithophores in the world oceans, responded to low-latitude insolation seasonality variation induced by the 405,000-year (405-ky) eccentricity cycle, suggesting that insolation seasonality directly forced marine ecology and marine carbon cycles. However, the proxy evidence of the influence on the carbon cycles is lacking. In this study, we applied our new proxy of the carbonate-organic matter “rain ratio,” the concentration ratio of alkenone K₃₇ to crenarcheol, [the K₃₇/Cren ratio] to reconstruct the Noelaerhadaceae export in Sites U1446 (the Bay of Bengal) and U1486 (the Bismarck Sea) to understand the role of Noelaerhadaceae in marine carbon cycles. The K₃₇/Cren ratio synchronized in Sites U1446 and U1486 over the past 1.5 million years, showing minima at ~1280 (MIS-37), 1100 (MIS-31), 800 (MIS-21), 400 (MIS-11), and 0 ka (MIS-1) when eccentricity was low. The minimum periods correspond to when the atmospheric CO₂ concentration peaked. The long-term variation of the K₃₇/Cren ratio resembles that of benthic foraminifera δ¹³C in the deep Pacific. This correspondence suggests that the insolation seasonality variation induced by the 405-ky eccentricity cycle influenced global marine carbon cycles via changes in Noelaerhadaceae production in tropical oceans.