Conflicting sets of hypotheses highlight either the role of ice sheets or atmospheric carbon dioxide (CO2) in causing the increase in duration and severity of ice age cycles ∼1 Mya during the Mid-Pleistocene Transition (MPT). We document early MPT CO2 cycles that were smaller than during recent ice age cycles. Using model simulations, we attribute this to post-MPT increase in glacial-stage dustiness and its effect on Southern Ocean productivity.

Global climate and the atmospheric partial pressure of carbon dioxide (pCO2atm ) are correlated over recent glacial cycles, with lower pCO2atm during ice ages, but the causes of the pCO2atm changes are unknown. The modern Southern Ocean releases deeply sequestered CO2 to the atmosphere.

Global climate and the atmospheric partial pressure of carbon dioxide (pCO2atm ) are correlated over recent glacial cycles, with lower pCO2atm during ice ages, but the causes of the pCO2atm changes are unknown. The modern Southern Ocean releases deeply sequestered CO2 to the atmosphere.