Ice sheet influence on atmospheric circulation explains the patterns of Pleistocene alpine glacier records in North America

We explore the hypothesis that the relative size of Pleistocene ice sheets in North America modulated regional climate and alpine glaciation. We compare Pleistocene alpine glacier chronologies across North America with a comprehensive general circulation model using reconstructed ice sheet extents at peak glacial conditions during Marine Isotope Stage (MIS) 2 and MIS 4. The effect of continent-wide ice sheets on atmospheric circulation during MIS 2 led to warming in Beringia and cooling in the western US; less expansive ice sheets during MIS 4 resulted in weaker ice sheet modulation of atmospheric circulation. This led to preservation of MIS 4 moraines in Beringia due to limited MIS 2 glaciation (resulting in a MIS 2/4 moraine sequence) and overriding of MIS 4 moraines – for sites with existing chronologies – in the western United States during MIS 2 (resulting in a MIS 2/6 moraine sequence). Our results highlight how influential ice sheets are for regional climate conditions.