Dynamics of ~100-kyr glacial cycles during the early Miocene

Abstract

Here, we present high-resolution stable isotope records from ODP Site 1264 in the South-Eastern Atlantic Ocean, which resolve the latest Oligocene to early Miocene (23.7–18.9 Ma) climate changes. Using an inverse modelling technique, we decom- posed the oxygen isotope record into temperature and ice volume and found that the Antarctic ice sheet expanded during distinct episodes (e.g., Mi zones) of low short-term (∼100-kyr) eccentricity forcing, which occur two to four long-term (400-kyr) eccentricity cycles apart. We argue that a non-linear mechanism, such as the merging of (several) large East Antarctic ice sheets, caused the build-up of a larger ice sheet. During the termination phases of these larger ice sheets, on the contrary, we find a more linear response of ice-sheet variability to orbital forcing and climate became highly sensitive to the ∼100-kyr eccentricity cycle. At the Oligocene-Miocene transition the model output indicates a decrease in Northern Hemisphere temperatures such that a small ice cap could develop on Greenland. This supports the hypothesis of a threshold response for the development of Northern Hemisphere land ice to decreasing pCO2.