![]() ![]() Both the deoxygenation and temperature increase over the shelf as well as the freshening of the subpolar Atlantic, have been attributed to increased transport of Labrador Current Water within the subpolar North Atlantic, at the expense of the Slope Sea and the eastern American continental shelf 4, 11. From 2012 to 2016, the subpolar North Atlantic experienced a strong freshening 11, with potential impacts on the Atlantic meridional overturning circulation (AMOC) 11, 12. Lawrence Estuary 4, 5 and the Gulf of Maine 6, 7, with dire consequences on marine ecosystems 8, 9 and fisheries 7, 10. Over the last decades, the Slope Sea and northeastern American continental shelf have experienced an increase in water temperatures and a decrease in oxygen concentrations 1, 2, 3, including in connected bodies of water such as the St. A mechanistic understanding of the drivers of the Labrador Current retroflection should help predict changes in the water properties in both export regions, and anticipate their impacts on marine life and deep-water formation. Starting in 2008, a particularly strong northward shift of the Gulf Stream dominates the other drivers. ![]() Here, we develop a retroflection index based on the pathway of virtual Lagrangian particles and show that strong retroflection generally occurs when a large-scale circulation adjustment, related to the subpolar gyre, accelerates the Labrador Current and shifts the Gulf Stream northward, partly driven by a northward shift of the wind patterns in the western North Atlantic. The relative contribution of these waters to either region depends on the eastward retroflection of the Labrador Current at the Grand Banks of Newfoundland. The Labrador Current transports cold, relatively fresh, and well-oxygenated waters within the subpolar North Atlantic and towards the eastern American continental shelf. ![]()
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