The onset of the Younger Dryas, a brief cold period in Western Europe 12,700 years ago, occurred over the course of a single year, reports a study published online this week in Nature Geoscience. The study suggests that the cold, stormy conditions were the result of an abrupt shift in atmospheric circulation over Europe.
Achim Brauer and colleagues studied varved sediments from a German crater lake. Each varve records a single year, allowing annual climate records from the region surrounding the lake to be reconstructed. The team found that from one year to the next, formation of an iron mineral in the sediments abruptly stopped. They link this to an increase in wind strength and storminess across Europe.
Today, westerly winds bring relatively warm moist air, heating Western Europe. The researchers conclude that during the Younger Dryas the westerlies instead brought cold air from the north, freezing the continent.