Gulf Stream contribution to recent North Pacific warming

Abstract

Recent unprecedented ocean warming has produced coherent sea surface temperature (SST) anomalies across the Northern Hemisphere extratropics. While the tropical Pacific is a natural source of North Pacific variability, the influence of the midlatitude North Atlantic has remained poorly understood. Here we show that Gulf Stream SST variability remotely modulates Kuroshio variability, explaining 13% of internal Kuroshio SST variance in climate model simulations, with no significant reverse influence. Positive Gulf Stream SST anomalies excite a Northern Annular Mode (NAM)-like atmospheric circulation response, weakening the Aleutian Low over the North Pacific. The resulting northward shift of the Kuroshio Extension enhances northward warm-water transport and favors positive SST anomalies in the western midlatitude North Pacific. We also show that a high-resolution ocean model is required to properly capture this SST-NAM coupling, suggesting the importance of representations of western boundary currents and associated SST fronts for this interbasin pathway. These findings reveal the Gulf Stream-Kuroshio linkage through which North Atlantic variability has measurably contributed to the recent exceptional North Pacific warming, implying a previously underrecognized source of decadal climate predictability.