Millennial-scale Northern Hemisphere ice sheet growth controlled by stadial-versus-interstadial duration

Global sea-level changes are significantly associated with variations in Northern Hemisphere ice sheets (NHISs) during the last glacial cycle. However, their responses to glacial millennial-scale climate variability (also known as Dansgaard - Oeschger (DO) cycles), especially during the Marine Isotope Stage 3 (MIS3, ~30-65ka), remains poorly studied, in addition to the contrast lines of geological evidence regarding paleo-sea level changes. Instead of applying Glacial Index Method which overlooks potential tempo-spatial heterogeneity of temperature and precipitation in the northern high latitudes, in this study, we conducted transient PISM ice sheet modeling by imposing full climate forcing derived from fully coupled climate model experiments which are characterized by spontaneous millennial variability. Our results show that control factors of ice volume changes in Laurentide and Eurasian ice sheets are different due to spatially heterogenous climate forcing. During stadial periods, North American Ice sheets is growing because of increased precipitation especially along the margins of the ice sheets, despite spatially heterogenous but trivial changes in the surface air temperature. Meanwhile, dramatic cooling on the southern regions of Eurasian Ice sheets effectively reduces ice loss and hence promote the overall ice growth. In brief, NHIS ice volume grows during stadials while declines during interstadials. We hence propose that stadial-to-interstadial duration ratio is the key to the net change in NHIS volume in a signal DO cycle, providing dynamic understanding of accelerated sea level drop during 40-30ka.