Gulf Stream drives Kuroshio behind the recent abnormal ocean warming

Abstract: Recent unprecedented ocean warming has produced coherent sea surface temperature (SST) anomalies across the Northern Hemisphere extratropics. Despite extensive research on inter-basin interactions, the causal mechanisms linking North Pacific and North Atlantic variability remain poorly understood. Here we show that internal SST variability in the Gulf Stream region accounts for 16% of internal SST variability in the Kuroshio region in climate model simulations, while no significant reverse influence is detected. Specifically, positive SST anomalies in the Gulf Stream excite a Northern Annular Mode (NAM)-like atmospheric circulation pattern, that weakens the Aleutian Low over the North Pacific. The resulting northward shift of the Kuroshio Extension enhances northward warm water transport and induces positive SST anomalies in the North Pacific. Climate models with higher oceanic spatial resolution capture this SST-NAM coupling substantially better than coarser-resolution models. These findings identify North Atlantic variability as a key pacemaker of Northern Hemisphere mid-latitude climate, with implications for understanding and predicting the accelerated ocean warming observed across the Northern Hemisphere in recent decades.