Response of North American ice sheets to the Younger Dryas cold reversal (12.9 to 11.7 ka)

The Younger Dryas (YD; 12.9 to 11.7 thousand years before present [ka]) was an abrupt cooling event in the North Atlantic region that interrupted the last deglaciation. This interval is an important analogue for ice inception and provides key insights into the impacts of millennial-scale climatic excursions on the broad Earth System. However, the effect of YD cooling on North American ice sheets – by far the largest ice masses in the Northern Hemisphere at that time – is poorly understood. Here, we document our current level of knowledge in ice margin behavior (stabilization, advance or continued retreat) that occurred to North American ice sheets during the YD interval. We assign a quality score for each segment of the YD ice margin that takes into account (i) our degree of confidence in the YD ice position (e.g. whether prominent moraines were formed) and (ii) the quality of chronological control on the ice position (e.g. assumed vs. directly dated). We divide the North American ice sheets into 11 regions and discuss changes in behavior during the YD interval. In some cases, our level of knowledge on the local YD ice margin behavior and chronological control is good (e.g. Ten Mile Lake moraine [Newfoundland], Collins Pond Phase [Atlantic Canada], Grand Marais I moraine, Dog Lake moraine, Hartman-Lac Seul moraine [all in the region of Lake Superior], and Cree Lake moraine [northern Saskatchewan]). In other cases, our knowledge is poor, and the ice margin behavior and age assignment are inferred or interpolated across the broad region. We also bring together paleoclimate data from 155 sites (largely lakes, ponds and peatlands) situated near the YD ice margin to provide additional context for any local or regional climate variations during that interval and to explore potential linkages between cooling and nearby ice margin behavior. We finish by discussing YD ice sheet response in other areas (ie. Greenland and Fennoscandia); outlining the possible mechanisms for YD cooling; delving into numerical modelling through the YD interval and suggesting future improvements in empirical and numerical approaches.