Interannual Atmospheric Variability Affects Continental Ice Sheet Simulations on Millennial Time Scales

Abstract

To inform the ongoing development of earth system models that aim to incorporate interactive ice, the potential impact of interannual variability associated with synoptic variability and El Niño?Southern Oscillation (ENSO) at the Last Glacial Maximum (LGM) on the evolution of a large continental ice sheet is explored through a series of targeted numerical modeling experiments. Global and North American signatures of ENSO at the LGM are described based on a multidecadal paleoclimate simulation using an atmosphere?ocean general circulation model (AOGCM). Experiments in which a thermomechanical North American ice sheet model (ISM) was forced with persistent LGM ENSO composite anomaly maps derived from the AOGCM showed only modest ice sheet thickness sensitivity to ENSO teleconnections. In contrast, very high model sensitivity was found when North American climate variations were incorporated directly in the ISM as a looping interannual time series. Under this configuration, localized transient cold anomalies in the atmospheric record instigated substantial new ice formation through a dynamically mediated feedback at the ice sheet margin, altering the equilibrium geometry and resulting in a bulk 10% growth of the Laurentide ice sheet volume over 5 kyr.