ENERGY MOISTURE BALANCE MODEL SIMULATIONS OF LAURENTIDE ICE SHEET MASS BALANCE RESPONSES TO EARLY HOLOCENE ENHANCED BOREAL SUMMER INSOLATION

Understanding the primary mechanisms and feedbacks responsible for past ice sheet retreat can provide information for determining the response of the Greenland Ice Sheet to future climate change. To first order, the fate of the ice sheets can be assessed by calculating the mass balance of the ice sheets, which neglects the higher-order responses such as ice deformation, ice dynamic feedbacks, basal sliding, and hard or soft bed conditions, which tend to expedite ice sheet decay. The most recent example of a large ice sheet occurred during the early Holocene, when the Laurentide Ice Sheet (LIS) containing a mass roughly equivalent to two-times that of Greenland, completely disappeared. We present new simulations of the LIS mass balance response to enhanced early Holocene boreal summer insolation and attendant climate warming using a physically based energy moisture balance model (EMBM) that improves on previous simplified estimates of the surface energy and mass balance of many ice sheet models. Forced with output from an Atmosphere-Ocean General Circulation Model simulation of 9 kyr BP climate, the EMBM simulates an LIS net mass balance of about -1.7 m/yr. This suggests that in order to match the geologic record of mass loss, two-thirds of the LIS mass was lost through enhanced ablation with the remaining mass removed by dynamic processes not accounted for in the model. These results imply that enhanced ablation may play a larger role in the future response of the Greenland Ice Sheet to global warming.