SPATIAL FINGERPRINTS AND MECHANISMS OF TEMPERATURE AND PRECIPITATION CHANGES DURING THE YOUNGER DRYAS IN EASTERN NORTH AMERICA

Recent temperature reconstructions based on a dense network of fossil-pollen and branched glycerol dialkyl glycerol tetraether records from across eastern North America demonstrate a complex response to Younger Dryas cooling in the North Atlantic. Sites north of 35°N cooled while south of 35°N the Younger Dryas was muted and sites in Florida experienced a thermal maximum. We aim to diagnose the spatial patterns and associated mechanisms of Younger Dryas climate change in eastern North America by comparing this network of temperature reconstructions and new precipitation reconstructions to three atmosphere-ocean general circulation models (AOGCM) with a freshwater forcing in the North Atlantic and the transient TraCE-21ka simulations. Reconstructed Younger Dryas precipitation changes present a coherent tripole pattern with wetting in the northeastern United States (US) and Florida, while a broad swath of drying is recorded from the Great Lakes Region to the Carolinas. These precipitation patterns contrast the reconstructed temperature dipole, but collectively indicate a warm/wet Younger Dryas in parts of the southeastern US. We quantitively compare these climate reconstructions to the AOGCMs using a spatially debiased metric of climate model skill. Of the AOGCM’s analyzed, the transient TraCE-21ka experiment most accurately simulates the reconstructed temperature and precipitation change in sign, magnitude, and spatial configuration, but lacks warming in Florida. The three hosing-only AOGCMs perform comparatively poorly, but all simulate regions of warming and wetting in eastern North America that is attributed to wind transport and mean sea level pressure anomalies shared among the three model simulations. These atmospheric changes over eastern North America are a response to an enhanced midlatitudinal jet onset from greater temperature gradients in the North Atlantic following a weakening of the Atlantic meridional overturning circulation.