Enhanced storm activities triggered the North Pacific deep convection during the Younger Dryas event

The occurrence of deep convection could redistribute ocean heat and materials, and induce robust climate and biogeochemical changes. The convection in the North Pacific is quite shallow now (typically 300-m), but paleo records and model simulations suggest that it might reach 2000-3000 m during stadials in the last deglaciation, such as the Heinrich event 1 (H1: ~17.5-15 ka) and Younger Dryas event (YD: ~12.8-11.5 ka). The deep convection during H1 has been explained by increased North Pacific surface salinity due to evaporation and precipitation changes, but this explanation conflicts with many paleo records for YD. Here we collected published paleo records in the northwest Pacific and carried out simulations for the YD period. We show that due to the weakened Atlantic Meridional Overturning Circulation (MOC) during YD, the oceanic Meridional Heat Transport (MHT) weakened. According to the Bjerknes compensation, the atmospheric MHT strengthened. Because atmospheric MHT mainly occurs through baroclinic eddies in extratropics, storm activities strengthened. The strengthened wintertime storm activities induced more oceanic turbulent heat loss and triggered deep convections in the North Pacific, and further contributed to a seesaw pattern of MOC strengths between the North Pacific and North Atlantic. Our result not only provides a new explanation for the North Pacific deep convection during YD but also suggest that synoptic-scale atmospheric variations are capable of influencing low-frequency paleoclimate changes.