Evolution and dynamics of the flow through Herald Canyon in the western Chukchi Sea

The flow of summer and winter Pacific water masses through Herald Canyon is investigated using data from a high-resolution hydrographic/velocity survey conducted in summer 2004. The survey was part of the Russian-American Long Term Census of the Arctic (RUSALCA) program, and consisted of four cross-canyon transects occupied over a 2-day period. At the time of the survey dense winter water was entering the western side of the canyon from the Chukchi Sea, flowing alongside a poleward jet of summer water on the canyon’s eastern flank. As the dense water progressed northward it switched sides of the canyon and underwent a sudden increase in layer thickness. This coincided with vertical mixing near the interface of the winter and summer water, producing a new water mass mode exiting the canyon. All of these features are consistent with the notion of hydraulic activity occurring in the canyon. A three-layer hydraulic theory is applied to the flow, which suggests that it is supercritical and that hydraulic control is likely. A lock-exchange formulation accurately predicts the northward transport of the winter water. The origin of the winter water and the manner in which it drains into the canyon is investigated using satellite ice-concentration data, atmospheric re-analysis fields, historical in-situ data, and a simple circulation model. Finally, the fate of the Pacific water exiting the canyon, and its connection to the Chukchi shelfbreak current, is discussed.