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Abstract The Subpolar North Atlantic is prone to recurrent extreme freshening events called Great Salinity Anomalies (GSAs). Here, we combine hydrographic ocean analyses and moored observations to document the arrival, spreading, and impacts of the most recent GSA in the Irminger Sea. This GSA is associated with a rapid freshening of the upper Irminger Sea between 2015 and 2020, culminating in annually averaged salinities as low as the freshest years of the 1990s and possibly since 1960. Upon the GSA propagation into the Irminger Sea over the Reykjanes Ridge, the boundary currents rapidly advected its signal around the basin within months while fresher waters slowly spread and accumulated into the interior. The anomalies in the interior freshened waters produced by deep convection during the 2017–2018 winter and actively contributed to the suppression of deep convection in the following two winters. 

Abstract The subpolar North Atlantic is a site of significant carbon dioxide, oxygen, and heat exchange with the atmosphere. This exchange, which regulates transient climate change and prevents large‐scale hypoxia throughout the North Atlantic, is thought to be mediated by vertical mixing in the ocean's surface mixed layer. Here we present observational evidence that waters deeper than the conventionally defined mixed layer are affected directly by atmospheric forcing in this region. When northerly winds blow along the Irminger Sea's western boundary current, the Ekman response pushes denser water over lighter water, potentially triggering slantwise convection. We estimate that this down‐front wind forcing is four times stronger than air–sea heat flux buoyancy forcing and can mix waters to several times the conventionally defined mixed layer depth. Slantwise convection is not included in most large‐scale ocean models, which likely limits their ability to accurately represent subpolar water mass transformations and deep ocean ventilation. 

Abstract The pathways and transports of Labrador Sea Water (LSW) within the southward‐flowing lower limb of the Atlantic Meridional Overturning Circulation are studied using 12 years of Argo profiles and subsurface Argo drift data. Consistent with previous studies, the results show clear evidence for interior pathways of LSW that separate from the western boundary near the Grand Banks and flow eastward and then southward around a large‐scale deep anticyclonic gyre in the northern subtropical Atlantic. Most of the LSW exported into the interior recirculates in the Newfoundland Basin (9.3 ± 3.5 Sv). However, approximately 3.2 ± 0.4 Sv cross the Mid‐Atlantic Ridge and flow southward east of the Azores. This branch feeds a westward quasi‐zonal pathway that recrosses the Ridge and returns to the western boundary around 30°N.