Lateglacial Shifts in Seasonality Reconcile Conflicting North Atlantic Temperature Signals

The accelerating flux of glacial meltwater to the oceans due to global warming is a potential trigger for future climate disturbance. Past disruption of Atlantic Ocean circulation, driven by melting of land-based ice, is linked in models to reduced ocean-atmosphere heat transfer and abrupt cooling during stadial events. The most recent stadial, the Younger Dryas (YD), is traditionally viewed as a severe cooling centered on the North Atlantic but with hemispheric influence. However, indications of summer warmth question whether YD cooling was truly year-round or restricted to winter. Here, we present a beryllium-10-dated glacier record from the north-east North Atlantic, coupled with 2-D glacier-climate modeling, to reconstruct Lateglacial summer air temperature patterns. Our record reveals that, contrary to the prevailing model, the last glacial advance in Scotland did not occur during the YD but predated the stadial, while the YD itself was characterized by warming-driven deglaciation. We argue that these apparently paradoxical findings can be reconciled with regional and global climate events by invoking enhanced North Atlantic seasonality-with anomalously cold winters but warming summers-as an intrinsic response to globally increased poleward heat fluxes.