There has been a progressive deepening of winter convection in the Labrador Sea since 2012, with the individual profile maximum depth exceeding 1800 m since 2014 and reaching 2100 m in 2016. This increase, during repeated positive phases of the winter North Atlantic Oscillation (NAO), resembles that during the formation of the record depth (2500 m) Labrador Sea Water (LSW) class in 1987–1994, attributed to repeated positive NAO forcing having provided critical preconditioning. The 2012–2016 LSW class is one of the deepest and most persistent ever observed (back to 1938). Year-round observations from profiling Argo floats since 2002 complemented by annual surveys are providing novel information on the seasonal-to-decadal evolution of LSW, such as its variable density, the recent multiyear preconditioning, and its 2016 density being the highest since the mid-1990s. These findings should help international observation programs and numerical model studies investigating LSW influences on the subpolar North Atlantic and Atlantic Meridional Overturning Circulation.

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