Modelling the Northern Hemisphere ice sheet evolution during the last deglaciation and MIS-11 with an ice sheet-ice shelf coupled model

Ice sheet models are essential tools for studying ice sheet dynamics in response to the climate evolution during the Quaternary glacial-interglacial cycles. Here, we develop a new version of the Northern Hemisphere ice sheet model (NHISM, Zweck and Huybrechts, 2005) by adding a user-friendly ice shelf module and other new characteristics, such as the configurable horizontal resolution and coupled sea level change. This new ice sheet-ice shelf coupled model is named NHISM1.1. The ice shelf module is based on the shallow shelf approximation, allowing simulation of ice stream advance into the ocean and the transformation between floating and grounded ice. NHISM1.1 is first used to conduct offline equilibrium ice-sheet simulations driven by observed present-day climate. It simulates a reasonable spatial distribution of the Northern Hemisphere ice sheets with a bias of less than 10% in the Greenland Ice Sheet volume compared to observation. We then use NHISM1.1 to perform offline transient ice sheet simulations for two distinct periods in the past, the Last Deglaciation and the entire MIS-11 period. In both cases, NHISM1.1 is driven by climate outputs of transient simulations performed with the LOVECLIM1.3 model. The performance of NHISM1.1 and the influence of various model configurations are evaluated by comparison with proxy reconstructions and other model simulations as well as sensitivity experiments. Our ice sheet simulations show that the NH ice sheets are largely consistent with geological evidence and that the incorporation of an ice shelf module is critical in properly reproducing glacial inception. By combining the analysis of climate simulations from LOVECLIM1.3 and offline ice sheet simulations from NHISM1.1, we propose that insolation plays a dominant role in driving the initial cooling of the Northern Hemisphere and the regrowth of its ice sheets during the MIS-11 glacial inception.