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Abstract Cross‐shelf exchange at Greenland's continental margins transports warm waters toward the glacier margins and freshwater offshore into the convective basins of the North Atlantic and Nordic Seas. Several studies have suggested that the exchange is enhanced by the presence of deep, glacial troughs, but observations from Greenland's troughs are scarce. This work presents data from a ship‐based survey at Narsaq Trough, a wide, branched trough in southwest Greenland, during the summer of 2022. We use Conductivity‐Temperature‐Depth‐Oxygen profiles, water samples for nutrient analysis, and underway current profiles to compare the water mass properties and distribution inside and outside the trough, describe the flow‐field in and around the trough, and estimate mixing in the trough. Narsaq Trough is found to provide a pathway for warm, salty Atlantic Water to intrude onto the continental shelf where these waters are mixed with the overlying cold, fresh Polar Water. As a result, waters in the trough are fresher, oxygen‐enriched, macronutrient‐depleted, and at times colder, relative to the unmodified Atlantic Water offshore. This trough‐modified water has the potential to freshen and oxygenate the flow on the shelf‐break and/or reduce the thermal forcing of waters in the adjacent fjord, limiting ice melt. 

Abstract Global climate change has impacted ocean biogeochemistry and physical dynamics, causing increases in acidity and temperature, among other phenomena. These changes can lead to deleterious effects on marine ecosystems and communities that rely on these ecosystems for their livelihoods. To better quantify these changes, an array of floats fitted with biogeochemical sensors (BGC‐Argo) is being deployed throughout the ocean. This paper presents an algorithm for deriving a deployment strategy that maximizes the information captured by each float. The process involves using a model solution as a proxy for the true ocean state and carrying out an iterative process to identify optimal float deployment locations for constraining the model variance. As an example, we use the algorithm to optimize the array for observing ocean surface dissolved carbon dioxide concentrations (pCO₂) in a region of strong air–sea gas exchange currently being targeted for BGC‐Argo float deployment. We conclude that 54% of the pCO₂variability in the analysis region could be sampled by an array of 50 Argo floats deployed in specified locations. This implies a relatively coarse average spacing, though we find the optimal spacing is nonuniform, with a denser sampling being required in the eastern equatorial Pacific. We also show that this method could be applied to determine the optimal float deployment along ship tracks, matching the logistics of real float deployment. We envision this software package to be a helpful resource in ocean observational design anywhere in the global oceans. 

Abstract Watermass transformation in the Irminger Sea, a key region for the Atlantic Meridional Overturning Circulation, is influenced by atmospheric and oceanic variability. Strong wintertime atmospheric forcing in 2015 resulted in enhanced convection and the densification of the Irminger Sea. Deep convection persisted until 2018, even though winters following 2015 were mild. We show that this behavior can be attributed to an initially slow convergence of buoyancy, followed by more rapid convergence of buoyancy. This two‐stage recovery, in turn, is consistent with restratification driven by baroclinic instability of the Irminger Current (IC), that flows around the basin. The initial, slow restratification resulted from the weak horizontal density gradients created by the widespread 2015 atmospheric heat loss. Faster restratification occurred once the IC recovered. This mechanism explains the delayed recovery of the Irminger Sea following a single extreme winter and has implications for the ventilation and overturning that occurs in the basin.