Geological evidence for modeled Younger Dryas ice expansion in northern Maine is assessed in conjunction with temperature and precipitation estimates from chironomids and pollen, and plant macrofossil and lake-level analyses from lake sediment. Pollen and chironomid temperature and precipitation transfer-function estimates for the Allerød warming period indicate colder winters, precipitation levels half that of modern times, and summer temperatures near modern levels. The combination of cold winters and low precipitation prevented forest establishment in northern Maine along the Maine/New Brunswick border. While winter temperatures and precipitation remained stable, summer temperatures decreased as much as 7.5 °C during the Younger Dryas stadial, forcing a shift from shrub-dominated to sedge-dominated tundra. Summer and winter temperatures, as well as annual precipitation, increased rapidly at the Holocene onset.
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