Rapid deglaciation of eastern Maine, northeastern North America, during Heinrich Stadial 1

Despite decades of research, we do not have a complete understanding of what causes ice-age terminations. Apparently contradictory climate records from the North Atlantic region during Heinrich Stadial 1 (HS1) have led to the concept of extreme seasonality, with warming summers and bitterly cold winters. Here, we assess the hypothesis of warming summer temperatures during HS1 from a record of ice-sheet behavior in eastern Maine, northeastern North America. Forty-five new ¹⁰Be cosmogenic exposure ages, along with previously published ¹⁰Be ages and numerous onshore and offshore radiocarbon dates, present an internally consistent picture of rapid ice retreat during HS1 from at least ∼17-15 ka. Exposure ages show deglaciation along a 160 km north-south transect in eastern Maine was centered on 15.3 ± 0.5 ka and occurred within the error of the dating method. Although we cannot rule out any marine influence (at least at the start of deglaciation), we attribute the primary underlying cause of this recession to warming summer temperatures, particularly once the ice margin became terrestrial. These results are consistent with the concept of strong seasonality during North Atlantic stadial events, such as HS1, that may have its origin in summertime meltwater from retreating ice sheets leading to the development of winter sea ice and concurrent frigid winter temperatures.