Southern Ocean upwelling, Earth’s obliquity, and glacial-interglacial atmospheric CO 2 change

Controlling atmospheric carbon dioxide The atmospheric concentration of carbon dioxide (CO 2 ) has varied substantially over the past million years in tandem with the glacial cycle. Although it is widely agreed that upwelling of Southern Ocean water is a key factor, the finer details about what caused these CO 2 variations are of great importance for understanding climate. Ai et al. identified three modes of change in Southern Ocean upwelling, adding a third to two previously recognized ones. This new mode can help explain better the relative timing of the glacial and CO 2 cycles. Science , this issue p. 1348