Northward Shifts in the Polar Front Preceded Bølling and Holocene Warming in Southwestern Scandinavia

The last deglaciation in northern Europe provides an opportunity to study the hydrologic component of abrupt climate shifts in a region with complex interactions between ice sheets and oceanic and atmospheric circulation. We use leaf wax hydrogen isotopes (δ2H) to reconstruct summer precipitation δ2H and aridity in southwestern Norway from 15.8 to 11.5 ka. We identify transitions to a more proximal moisture source before the ends of Heinrich Stadial 1 and the Younger Dryas, prior to local warming and increased primary productivity in both instances. We infer these changes in moisture delivery to southwestern Norway to be a response to northward shifts in the polar front caused by warm water intrusion into the North Atlantic, which preceded abrupt warming in the circum‐North Atlantic. These results suggest that moisture transport pathways shift northward as warm surface ocean water reaches higher latitudes in the North Atlantic. Plain Language Summary The end of the last glacial maximum (~22,000 to 11,600 years ago) in northern Europe contains two particularly abrupt warming events that occurred around 14,600 and 11,600 years ago. These past warming events provide an opportunity to study changes in precipitation and other aspects of hydrology during abrupt temperature increases. We use the ratio of stable isotopes of hydrogen in leaf waxes preserved in lake sediments to reconstruct changes in the transport path length of summer precipitation in southwestern Norway during the Lateglacial 15,800 to 11,600 years ago. We identify changes in precipitation hydrogen isotopes that indicate moisture started coming from sources closer to Norway before this region warmed at the entrance to the Bølling interstadial approximately 14,600 as well as the start of the Holocene 11,600 years ago. We infer these changes in moisture delivery to southwestern Norway to be a response to northward shifts in the polar front caused by sea ice retreat and warm water moving into the North Atlantic, which preceded abrupt terrestrial warming in the circum‐North Atlantic. These results suggest that moisture transport pathways shift northward as warmer surface water reaches higher latitudes in the North Atlantic. Key Point Changes in moisture transport path length to southwestern Scandinavia preceded local summer warming during deglaciation