Strengthening of Labrador Sea overturning linked to subsurface freshening over recent decades

The Labrador Sea is a key formation site for dense waters that contribute to the lower limb of the Atlantic meridional overturning circulation (AMOC). Recent observations have revealed a distinctly weak overturning in this basin, attributed to compensating effects of temperature and salinity anomalies on density. However, it remains unclear whether these effects are consistent under varying hydrographic conditions and whether they subsequently impact overturning variability. By combining moored observations and historical hydrographic data, we demonstrate a coherent response of the Labrador Sea overturning to salinity anomalies over recent decades. Notably, a strengthened overturning in the late 2010s can be attributed to subsurface fresh anomalies advected into the basin by the boundary currents, which are linked to large-scale freshening that began in the late 2000s. Our findings underscore the necessity of continuously monitoring boundary salinity and temperature anomalies to capture ongoing changes in the Labrador Sea.