Letter abstract

The Younger Dryas event, which began approximately 12,900 years ago, was a period of rapid cooling in the Northern Hemisphere, driven by large-scale reorganizations of patterns of atmospheric and oceanic circulation^{1, 2, 3}. Environmental changes during this period have been documented by both proxy-based reconstructions³ and model simulations⁴, but there is currently no consensus on the exact mechanisms of onset, stabilization or termination of the Younger Dryas^{5, 6, 7, 8}. Here we present high-resolution records from two sediment cores obtained from Lake Kråkenes in western Norway and the Nordic seas. Multiple proxies from Lake Kråkenes are indicative of rapid alternations between glacial growth and melting during the later Younger Dryas. Meanwhile, reconstructed sea surface temperature and salinity from the Nordic seas show an alternation between sea-ice cover and the influx of warm, salty North Atlantic waters. We suggest that the influx of warm water enabled the westerly wind systems to drift northward, closer to their present-day positions. The winds thus brought relatively warm maritime air to Northern Europe, resulting in rising temperatures and the melting of glaciers. Subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice, which forced the westerly winds back to the south, cooling Northern Europe. We conclude that rapid alternations between these two states immediately preceded the termination of the Younger Dryas and the permanent transition to an interglacial state.