Equilibrium simulations of Marine Isotope Stage 3 climate
Abstract. An equilibrium simulation of Marine Isotope Stage 3 (MIS3) climate with boundary conditions characteristic of Greenland Interstadial 8 (GI-8; 38 ka BP) is carried out with the Norwegian Earth System Model (NorESM). A computationally efficient configuration of the model enables long integrations at relatively high resolution, with the simulations reaching a quasi-equilibrium state after 2500 years. We assess the characteristics of the simulated large-scale atmosphere and ocean circulation, precipitation, ocean hydrography, sea ice distribution, and internal variability. The simulated MIS3 interstadial near surface air temperature is 2.9 °C cooler than the pre-industrial (PI). The Atlantic Meridional Overturning Circulation (AMOC) is deeper and intensified (by ~ 13 %). There is a decrease in the volume of Antarctic Bottom Water (AABW) reaching the Atlantic. However, there is an increase in ventilation of the Southern Ocean, associated with a significant expansion of Antarctic sea ice and intensified brine rejection, invigorating ocean convection. In the central Arctic, sea ice is ~ 2 m thicker, with an expansion of sea ice in the Nordic Seas during winter. Simulated MIS3 inter-annual variability of the El Niño-Southern Oscillation (ENSO) and the Arctic Oscillation are weaker compared to the pre-industrial. Attempts at triggering a non-linear transition to a cold stadial climate state by varying atmospheric CO2 concentrations and Laurentide Ice Sheet height, suggest that the simulated MIS3 interstadial state in the NorESM is relatively stable, thus questioning the potential for unforced abrupt transitions in Greenland climate during the last glacial.