Pathways, timing, and evolution of Pacific Winter Water through Barrow Canyon

Abstract

Observations from a ship-based campaign in July-August 2009, combined with idealized numerical simulations, are used to investigate the seasonal delivery of Pacific Winter Water to Barrow Canyon and the subsequent adjustment of the flow down the canyon. As the current advects dense water, it transitions from a nearly barotropic structure near the canyon head to a strongly baroclinic flow with a subsurface maximum near the canyon mouth. Both the data and model indicate that the transit times along the three Chukchi Shelf pathways feeding Barrow Canyon – a coastal pathway, a southern Hanna Shoal pathway, and a northern Hanna Shoal pathway – modulate the mode of winter water that occupies the canyon at a given time. In particular, remnant Pacific Winter Water carried along the rapid coastal pathway can precede the arrival of newly ventilated Pacific Winter Water carried along the two interior pathways. The observations and model indicate that the transition between water types draining from the canyon can occur rapidly over time scales of days to weeks. We also demonstrate that mixing along the path of the current is unlikely to result in the observed down-canyon transition from newly ventilated Pacific Winter Water to remnant winter water, further supporting the dominant role of advection. While the focus here is on the transition of winter water modes, the implication that seasonality within Barrow Canyon is tied to seasonality of the Bering Strait inflow, together with the relative transit times along advective pathways, should hold for other water types as well.