[M-IS06] Evolution and variability of the Tropical Monsoon and Indo-Pacific climate during the Cenozoic Era

[MIS06-04] Pleistocene CO₂ variability inferred from the Bay of Bengal leaf wax carbon isotope records

*Masanobu Yamamoto¹, Tomohisa Irino¹, Renata Szarek¹, Osamu Seki³, Ayako Abe-Ouchi², Masakazu Yoshimori² (1.Faculty of Environmental Earth Science, Hokkaido University, 2.Atmospheric and Ocean Institute, University of Tokyo, 3.Institute of Low Temperature Science, Hokkaido University)

Keywords:CO2, proxy, marine core, Pleistocene

Atmospheric CO₂ and polar ice volume have been strongly coupled over the past 805,000 years. We have reconstructed the atmospheric CO₂ concentration throughout the Pleistocene since 2.6 million years ago (Ma) by exploiting the unique relationship between CO₂ concentration and leaf wax δ¹³C of IODP Sites U1445 and U1446 sediments, resulting from changes in the extent of C₃ and C₄ vegetation in eastern India. Notably, reconstructed interglacial CO₂ concentrations (CO₂^FA) in the early Pleistocene (Gelasian and Calabrian) were lower than pre-industrial levels, in agreement with recent results from Antarctic blue ice gas analysis. The CO₂^FA variation consistently covaries with benthic oxygen isotope variation throughout the Pleistocene, but more significantly after 1.6 Ma, indicating that the strong coupling between CO₂ and continental ice volume began at 1.6 Ma. The CO₂^FA variation shows the amplitude modulation on the ~400,000-year cycle; the amplitude is larger when the long-term eccentricity is lower. This variation is consistent with variations in the strength of the Antarctic Circumpolar Current and rain ratios (CaCO₃/OC, CaCO₃/opal, etc.) in the subpolar oceans. These results suggest that, in addition to the ice-CO₂ interaction, Southern Ocean upwelling and biological production regulated CO₂ variability during the Pleistocene.