Increased interglacial atmospheric CO2 levels followed the mid-Pleistocene Transition

Abstract

Atmospheric CO2 and polar ice volume have been strongly coupled over the past 805,000 years. However, the prior extent of coupling, during times of lower-amplitude ice-volume variability, is unknown because continuous high-resolution CO2 records are lacking. We reconstructed the past 1,460,000 years of atmospheric CO2 (~1,700 year sample resolution) by taking advantage of the unique relationship between CO2 concentration and leaf-wax δ13C resulting from changes in the extent of C3 and C4 vegetation in East India. Notably, reconstructed interglacial CO2 concentrations were lower before the transition to large volume variability during the mid-Pleistocene Transition (900,000 years ago). Prior to the mid-Pleistocene Transition, CO2 exhibited a secular trend similar to that of deep-ocean carbon isotopes. At orbital time scales, phase analysis indicates that the CO2 lead relative to ice volume changed to a lag during the mid-Pleistocene Transition. Combined, these findings suggest that deep-ocean circulation controlled the long-term CO2 trend, and that interaction between CO2, continental ice and deep-ocean circulation was reorganized during the mid-Pleistocene Transition, involving a decrease in carbon storage in the deep Pacific.