Spatial Fingerprint of Younger Dryas Cooling and Warming in Eastern North America.

The Younger Dryas (YD, 12.9–11.7 ka) is the most recent, near‐global interval of abrupt climate change with rates similar to modern global warming. Understanding the causes and biodiversity effects of YD climate changes requires determining the spatial fingerprints of past temperature changes. Here we build pollen‐based and branched glycerol dialkyl glycerol tetraether‐based temperature reconstructions in eastern North America (ENA) to better understand deglacial temperature evolution. YD cooling was pronounced in the northeastern United States and muted in the north central United States. Florida sites warmed during the YD, while other southeastern sites maintained a relatively stable climate. This fingerprint is consistent with an intensified subtropical high during the YD and demonstrates that interhemispheric responses were more complex spatially in ENA than predicted by the bipolar seesaw model. Reduced‐amplitude or antiphased millennial‐scale temperature variability in the southeastern United States may support regional hotspots of biodiversity and endemism. Plain Language Summary: The Younger Dryas, circa 12,900 to 11,700 years ago, is a hemispheric abrupt climate change event that occurred at rates similar to those projected by the 21st century. Its cause has been linked to a reduction in northward oceanic heat transport in the Atlantic that led to Northern Hemispheric cooling and Southern Hemispheric warming. Here we present detailed reconstructions of Younger Dryas temperature variations in eastern North America that suggest a more complex spatial fingerprint than predicted by the standard global model. New England, Maritime Canada, and the Great Lakes Region all cooled, like Greenland and elsewhere in the Northern Hemisphere. However, regions south of Virginia experienced little temperature change and Florida warmed slightly. Possible mechanisms include atmospheric processes that enhanced advection from the subtropics and oceanic processes that transported heat northward from the equatorial Atlantic. These reconstructions also help explain the hotspot of biodiversity and endemic species in the southeastern United States, by showing that this region was buffered from past abrupt millennial‐scale climate reversals. Key Points: The spatial fingerprint of Younger Dryas (YD) temperature changes is reconstructed in eastern North America from brGDGTs and fossil pollenReconstructions demonstrate higher YD temperatures in Florida, no change south of 40°N, and cooling north of 40°NThese patterns are consistent with intensified subtropical highs during the YD and help explain high regional biodiversity [ABSTRACT FROM AUTHOR]