Reconstructed CO2 variability over the entire Pleistocene inferred from sedimentary leaf wax carbon isotopes from the Bay of Bengal

Reconstructing past CO₂ concentrations is essential to understanding paleoclimates. However, the CO₂ record beyond the 805-ky ice core is insufficient to understand the relationship between CO₂ and climate. Results from new ice cores and blue ice samples are highly anticipated. Here, we present the proxy CO₂ record from the last 2.6 million years including the Mid-Pleistocene Transition, as determined by the δ¹³C values of sedimentary leaf waxes at IODP Site U1445, which reflect changes in the C₃/C₄ vegetation ratio in East Peninsular India. Our results show that interglacial CO₂ levels in the early Pleistocene were lower than preindustrial levels. Higher CO₂ levels occurred during super-interglacial periods. CO₂ covaries with benthic δ¹⁸O on the orbital timescale. A strong coupling continued throughout the Pleistocene. Interglacial CO₂ variation shows longer cycles averaging ~300 kyr, with several glacial cycles bunched together. A cycle begins with benthic δ¹⁸O and δ¹³C maxima in a glacial period, followed by an abrupt increase and subsequent decrease in interglacial CO₂ levels. This suggests that the collapse of large ice sheets triggered the release of accumulated ocean carbon into the atmosphere. The size of the glacial ice sheets and the accumulation of oceanic carbon controlled the extent of deglacial CO₂ release.