Session: Glacial Climates (LGM, Last deglaciation, Ice sheet uncertainties, Glacial-interglacial cycles)
Author: Sam Sherriff-Tadano / firstname.lastname@example.org / Atmosphere and Ocean Research Institute, the University of Tokyo
Co-author: Ayako Abe-Ouchi, Atmosphere and Ocean Research Institute, the University of Tokyo;
It has been shown from ice core reconstructions that glacial periods experienced frequent climate shifts between interstadials and stadials. The duration of these climate modes varied during glacial periods, and both the interstadials and stadials were shorter during Marine Isotope Stage 3 (MIS3) compared to MIS5. Recent studies showed that the duration of the interstadials is controlled by the Antarctic temperature, which has an impact on the stability of the Atlantic Meridional Overturning Circulation (AMOC). However, a similar relation could not be found for the stadials, suggesting that another climate factor (e.g. differences in ice sheet size, greenhouse gases and insolation) may play a role. Thus, for a better understanding of the stability of the climate, it is very important to evaluate the impact of these climate factors on the duration of the stadials. In this study, we investigate the role of glacial ice sheets. For this purpose, freshwater hosing experiments are conducted with an atmosphere-ocean general circulation model MIROC4m under several ice sheet configurations computed in an ice sheet model Icies (Abe-Ouchi et al. 2013). The impact of glacial ice sheets on the duration of the stadials is evaluated by comparing the behavior of the weak AMOC after the freshwater forcing is reduced. All experiments show a drastic weakening of the AMOC in response to the freshwater hosing, accompanied by a cooling over the North Atlantic, a southward shift of the tropical rain belt and a warming over the Antarctic. We find that experiments with smaller ice sheets take longer to recover after the freshwater hosing is reduced. Sensitivity experiments with MIROC4m reveal that differences in surface winds are important in causing the shorter stadial with larger ice sheet configurations, while differences in the surface cooling have an opposite effect.