An 800-kyr record of global surface ocean δ18O and implications for ice volume-temperature coupling

a r t i c l e i n f o a b s t r a c t Keywords: marine oxygen isotope record glacial cycles Pleistocene ice volume global temperature The sequence of feedbacks that characterized 100-kyr glacial cycles of the past million years remains uncertain, hampering an understanding of the interconnections between insolation, ice sheets, greenhouse gas forcing, and climate. Critical to addressing this issue is an accurate interpretation of the marine δ 18 O record, the main template for the Ice Ages. This study uses a global compilation of 49 paired sea surface temperature-planktonic δ 18 O records to extract the mean δ 18 O of surface ocean seawater over the past 800 kyr, which we interpret to dominantly reflect global ice volume. The results indicate that global surface temperature, inferred deep ocean temperature, and atmospheric CO 2 decrease early during each glacial cycle in close association with one another, whereas major ice sheet growth occurs later in glacial cycles. These relationships suggest that ice volume may have exhibited a threshold response to global cooling, and that global deglaciations do not occur until after the growth of large ice sheets. This phase sequence also suggests that the ice sheets had relatively little feedback on global cooling. Simple modeling shows that the rate of ice volume change through time is largely determined by the combined influence of insolation, temperature, and ice sheet size, with possible implications for the evolution of glacial cycles over the past three million years.