Rapid subsurface warming in the subpolar North Atlantic from freshening

Over recent decades, the Arctic has warmed four times faster than the global average, associated with a decline in sea ice and accelerating Greenland Ice Sheet mass loss, which has contributed to episodic freshening of the subpolar North Atlantic. Here, we show that a 0.05 Sv North Atlantic meltwater flux induces ~ 1°C subsurface warming within a decade in Baffin Bay, Hudson Strait, and along Greenland's southern and western coasts. This warming arises from enhanced stratification, weakened deep convection in the subpolar gyre, and a weaker Labrador Current. Freshening also alters horizontal density gradients, strengthening cyclonic circulation in the Nordic Seas and causing transient regional warming. The temperature response significantly depends on the location of deep-ocean convection, highlighting the need for simulations with accurate deep-ocean convection. This warming may create a positive feedback, accelerating Greenland and Arctic glacier melt with implications for ice-sheet stability and the strength of the Atlantic Meridional Overturning Circulation.