Freshwater‐Induced Surface Cooling of the Subpolar North Atlantic in a Large‐Ensemble, High‐Resolution, Coupled Model

Abstract

As a gateway between the Arctic and subtropics, the subpolar North Atlantic plays a key role in large‐scale climate variability. In recent decades, the region has experienced pronounced freshening. While much attention has been paid to the expected long‐term weakening of the Atlantic Meridional Overturning Circulation, the impact of freshwater on surface fluxes and seasonal to decadal air‐sea coupling remains poorly understood. Here, we explore the detailed mechanism by which the sea surface salinity in the subpolar gyre is linked to the local sea surface cooling with the CANARI Large Ensemble of the HadGEM3‐GC3.1 climate model. Our analyses suggest that freshwater fluxes modulate upper ocean dynamics, which enhance local cooling in winter and can explain the North Atlantic warming hole without the need to invoke large‐scale ocean circulation changes as a driver. Moreover, by shaping the local air‐sea heat fluxes, the freshening can have further‐reaching implications.