Evidence for a variable and wet Younger Dryas in southern Alaska

Pollen, macro- and micro-fossils, and sedimentologic indicators in sediment cores from Discovery Pond (DP) in south-central Alaska indicate that the coldest interval of the last deglacation was coincident with the onset of the Younger Dryas (YD), around 12.8 cal ka. The multi-proxy record from DP together with a compilation of recently published YD records from southern Alaska and the adjacent northern Pacific Ocean shows that, during the course of the YD, temperatures increased, then reached a maximum sometime around 11 cal ka. At DP, a pronounced increase in the abundance of Isoëtes and Pediastrum, including species associated with oligotrophic lakes and known to respond to increased precipitation, combined with a reduction in wetland aquatics and an increase in the minerogenic component of the sediment, all indicate a shift from wetland to open-water conditions at around 12.2 cal ka. Similar to other evidence from southern Alaska, our proxy record from DP indicates an increase in temperature and effective moisture during the second half of the YD. An increase in winter precipitation might be associated with a deepening of the Aleutian low-pressure system and a northward shift in winter storm tracks, consistent with recent simulations by climate system models.