Warming of the subpolar North Pacific accelerated by sea ice retreat and wind changes

Abstract

Climate models predict that the Pacific will become the foremost reservoir of human-induced heat in the 21st century among all oceans, with the subpolar North Pacific (SPNP) emerging as the critical region for heat uptake. Recent observations detect alarming warming rates across the Sea of Okhotsk, the Bering Sea, and the Gulf of Alaska. Yet, processes by which these seas absorb and store the heat remain unclear. Here, by combining observational datasets and model experiments, we reveal that the heat uptake in these SPNP seas has accelerated since the 1970s due to sea-ice retreat and shifts in large-scale winds. Specifically, a decline in winter sea ice growth in shelf regions of the SPNP amplifies surface atmospheric warming. The warming in surface air temperature suppresses sensible heat release in the SPNP interior, resulting in increased heat uptake. Furthermore, altered North Pacific winds spin up the subpolar circulation gyre, propelling increased heat transport from lower latitudes into the SPNP seas. The surface-intensified warming in the SPNP enhances stratification and shoals the mixed layer, triggering more marine heatwaves and disrupting biogeochemical cycles.