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Recent observational studies have provided detailed descriptions of double‐diffusive staircases in the Beaufort Sea, characterized by well‐mixed intrusions between high‐gradient interfaces. These structures result from double‐diffusive convection, occurring when cooler fresh water lies atop the warmer saltier Atlantic water layer. In the present study, we investigate the spatial structure of such layers, by analyzing combined high resolution data from a subsurface mooring, a ship‐towed profiling conductivity‐temperature‐depth/ADCP package, and a free‐falling microstructure profiler. At large scale, the modular microstructure profiler data suggest a horizontal "ragged edge" of the layered water masses near the basin boundary. At smaller scales, the mooring data indicate that, in the 300–400 m depth interval, regions of layers abruptly appear. This laterally sharp (of the order of 100 m) interface is advected southwards, as shown by the shallow water integrated mapping system survey conducted nearby. Neither disruption nor formation of layers is directly observed in our data, and we thus interpret our observations as the stable and possibly recent abutment of a layered and an unlayered water masses, now globally advected southwards by a large scale flow. Plain Language Summary: Double‐diffusive layers, that is, a vertical alternating of constant and varying density layers in the stratification, are seen in the Arctic, but their exact generation and destruction mechanisms are still unknown. Their study is of primary importance since they set heat transfer rates in the Arctic Ocean. Using high resolution measurements, we document a watermass boundary between a layered and an unlayered regions, drifting southwards past our site due to a large scale mean flow. The edges are laterally sharp and have complicated structure. Neither formation of layers nor active destruction is detected in our measurements, and the sharp boundary is constant on time scales of days–weeks while being advected. Key Points: High resolution measurements show a sharp boundary between regions with and without double diffusive staircases in southeast Canada BasinThe transition from regions with to without staircases occurs on length scales of order 100 mNeither formation of layers nor active disruption is directly observed at the interface [ABSTRACT FROM AUTHOR]