Subsurface temperature maxima in the Labrador Sea and the subpolar North Atlantic

Deep and shallow subsurface temperature maxima (Tmax) in the Labrador Sea are found to be the result of anomalous freshwater input during past decades in particular during the early 1990s. The deep Tmax is associated with a specific water mass imported into the Labrador Sea. The shallow Tmax is of local origin and created by anomalous heat input in 1999, not eroded by surface buoyancy forcing in recent years. Both are associated with stability maxima: the deep Tmax is a barrier for maximum convection depth, the shallow Tmax separates the water in a layer ventilated by overturning and a layer modified through lateral fluxes only. The shallow Tmax is exported into the subpolar gyre. A complementary shallow Tmax in the Greenland Sea suggest a concerted response of deep convection regions to anomalous freshwater input: diminished vertical mixing and dominance of lateral heat/ salt fluxes underneath Tmax, shallow convection above it.