Modeled Greenland Ice Sheet evolution constrained by ice-core-derived Holocene elevation histories

Abstract. During the Holocene, the Greenland Ice Sheet (GrIS) experienced substantial thinning, with some regions losing up to 600 m of ice. Ice sheet reconstructions, paleoclimatic records, and geological evidence indicate that, during the Last Glacial Maximum, the GrIS extended far beyond its current boundaries and was connected with the Innuitian Ice Sheet (IIS) in the northwest. We investigate these long-term geometry changes and explore several possible factors driving those changes by using the Parallel Ice Sheet Model (PISM) to simulate the GrIS thinning throughout the Holocene period, from 11.7 ka ago to the present. We perform an ensemble study of 841 model simulations in which key model parameters are systematically varied to determine the parameter values that, with quantified uncertainties, best reproduce the 11.7 ka of surface-elevation records derived from ice cores, providing confidence in the modeled GrIS paleo evolution. We find that since the Holocene onset, 11.7 ka ago, the GrIS mass loss has contributed 5.3 ± 0.3 m to the mean global sea-level rise, which is consistent with the ice-core-derived thinning curves spanning the time when the GrIS and the Innuitian Ice Sheet were bridged. Our results suggest that the GrIS is still responding to these past changes, having raised the sea level by 23 ± 26 mm SLE ka−1 in the last 500 years. Our results have implications for future ice sheet evolution, which should account for this long-term transient trend.