Deglacial ice sheet meltdown: orbital pacemaking and CO2 effects
- 1Earth and Environmental Systems Institute, Pennsylvania State University, University Park, USA
- 2International Pacific Research Center, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, USA
- 3Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, USA
- 4Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, USA
- 5Department of Integrated Climate Change Projection Research, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
- 6Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Japan
Abstract. One hundred thousand years of ice sheet buildup came to a rapid end ∼25–10 thousand years before present (ka BP), when ice sheets receded quickly and multi-proxy reconstructed global mean surface temperatures rose by ∼3–5 °C. It still remains unresolved whether insolation changes due to variations of earth's tilt and orbit were sufficient to terminate glacial conditions. Using a coupled three-dimensional climate–ice sheet model, we simulate the climate and Northern Hemisphere ice sheet evolution from 78 ka BP to 0 ka BP in good agreement with sea level and ice topography reconstructions. Based on this simulation and a series of deglacial sensitivity experiments with individually varying orbital parameters and prescribed CO2, we find that enhanced calving led to a slowdown of ice sheet growth as early as ∼8 ka prior to the Last Glacial Maximum (LGM). The glacial termination was then initiated by enhanced ablation due to increasing obliquity and precession, in agreement with the Milankovitch theory. However, our results also support the notion that the ∼100 ppmv rise of atmospheric CO2 after ∼18 ka BP was a key contributor to the deglaciation. Without it, the present-day ice volume would be comparable to that of the LGM and global mean temperatures would be about 3 °C lower than today. We further demonstrate that neither orbital forcing nor rising CO2 concentrations alone were sufficient to complete the deglaciation.