Dynamics of ~100-kyr glacial cycles during the early Miocene
1Department of Earth Sciences, Faculty of Geosciences, Utrecht University. Budapestlaan 4, 3584 CD Utrecht, The Netherlands
2Department of Geological Sciences, University of Florida, 241 Williamson Hall, P.O. Box 112120, Gainesville, Florida 32611, USA
3Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
*now at: School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, European Way, Southampton SO14 3ZH, UK
**now at: Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
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 decomposed 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.