The stability of the West Antarctic Ice Sheet (WAIS) depends on ocean heat transport toward its base and remains a source of uncertainty in sea level rise prediction. The Antarctic Slope Current (ASC), a major boundary current of the ocean's global circulation, serves as a dynamic gateway for heat transport toward Antarctica. Here, we use observations collected from the Bellingshausen Sea to propose a mechanistic explanation for the initiation of the westward‐flowing ASC. Waters modified throughout the Bellingshausen Sea by ocean‐sea‐ice and ocean‐ice‐shelf interactions are exported to the continental slope in a narrow, topographically steered western boundary current. This focused outflow produces a localized front at the shelf break that supports the emerging ASC. This mechanism emphasizes the importance of buoyancy forcing, integrated over the continental shelf, as opposed to local wind forcing, in the generation mechanism and suggests the potential for remote control of melt rates of WAIS' largest ice shelves.

Abstract. The Labrador Sea is one of a small number of deep convection sites in the North Atlantic that contribute to the meridional overturning circulation. Buoyancy is lost from surface waters during winter, allowing the formation of dense deep water. During the last few decades, mass loss from the Greenland ice sheet has accelerated, releasing freshwater into the high-latitude North Atlantic. This and the enhanced Arctic freshwater export in recent years have the potential to add buoyancy to surface waters, slowing or suppressing convection in the Labrador Sea. However, the impact of freshwater on convection is dependent on whether or not it can escape the shallow, topographically trapped boundary currents encircling the Labrador Sea. Previous studies have estimated the transport of freshwater into the central Labrador Sea by focusing on the role of eddies. Here, we use a Lagrangian approach by tracking particles in a global, eddy-permitting (1/12∘) ocean model to examine where and when freshwater in the surface 30 m enters the Labrador Sea basin. We find that 60 % of the total freshwater in the top 100 m enters the basin in the top 30 m along the eastern side. The year-to-year variability in freshwater transport from the shelves to the central Labrador Sea, as found by the model trajectories in the top 30 m, is dominated by wind-driven Ekman transport rather than eddies transporting freshwater into the basin along the northeast.

Oceanic processes in the Southern Ocean and along the Antarctic margins influence Earth's climate on a global scale. The upper Southern Ocean has persistently warmed over the last century (Gille, 2008), which has been accompanied by an increase in heat content of the West Antarctic continental shelf (Schmidtko et al., 2014) and by increased glacial melting (Cook et al., 2016;Pritchard et al., 2012). The thinning of floating ice shelves throughout West Antarctic coastal seas, which includes the Amundsen and Bellingshausen seas as well as the northern part of the West Antarctic Peninsula (WAP) (Figure 1), is one of the most

Tracer distribution over the Bellingshausen shelf is presented with data from a comprehensive hydrographic survey.• Meltwater is present from mid-depth to surface and is accumulated toward the western shelf, consistent with a cyclonic gyre circulation.• The inferred overturning circulation driven by ice-shelf melting is comparable to previous estimates made in the neighboring Amundsen Sea.

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