Prolonged Heavy Snowfall During the Younger Dryas

摘要

Snowfall is an important component of Earth's climate system; however, long, continuous high-resolution records of global snowfall are lacking because of the absence of suitable proxies. In this study, diatom record from the sediments of Yunlong Lake, in the southeastern Tibetan Plateau, was used to reconstruct snowfall during the Younger Dryas (YD). Variations in the abundance of low-light-tolerant diatoms and diatom flux indicate that the duration of lake ice cover during the YD was significantly longer than that during the colder Heinrich event 1; this suggests that heavy snowfall, rather than temperatures, was responsible for the greater duration of lake ice cover during the YD. Thus, we conclude that prolonged, heavy snowfall occurred in the southeastern Tibetan Plateau during the YD. In addition, this conclusion is supported by the results of a climate model simulation that also suggest that heavy snowfall occurred at high latitude in the Northern Hemisphere during the YD. We propose that the heavy snowfall intensified cooling in Northern Hemisphere by increasing the albedo and that it increased hydrological variability at low latitudes by increasing the duration of the southward migration of the Intertropical Convergence Zone and by delaying the onset of the Asian summer monsoon. The snowfall would have been a source of continuous freshwater that acted as a positive feedback and resulted in a prolonged weakened state of the Atlantic meridional overturning circulation, which lasted for more than 1,000years. Overall, our results emphasize the amplification and positive feedback function of heavy snowfall in triggering abrupt climate change.