Shelfbreak downwelling in the Alaskan Beaufort Sea

Nicholas Foukal1, Robert S Pickart1, Kent Moore2 and Peigen Lin1, (1)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (2)Univ Toronto, Toronto, ON, Canada
Abstract:
The southern Beaufort Sea is characterized by frequent storms that redistribute sea ice and water masses along and across the continental shelf. Past studies have focused on upwelling-favorable storms, in which easterly winds transport surface waters offshore and bring water from the basin to the bottom of the shelf. In this presentation, the oceanographic response and atmospheric forcing associated with downwelling-favorable storms along the Alaskan Beaufort Sea shelf/slope will be described using in situ mooring data collected from August 2002 to September 2004, along with meteorological timeseries, reanalysis fields, and satellite ice concentration data. In total, 55 downwelling events occurred during the two-year period. The storms span all months of the year, with a peak in July and August. Downwelling is initiated by cyclonic low pressure systems displacing the Beaufort High and driving westerly winds over the region. The shelfbreak jet responds by accelerating to the east, followed by a depression of isopycnals along the outer-shelf and slope. The storms last 3.25 +/- 1.8 days, at which point conditions relax toward their mean state. For a given wind strength the largest response occurs during partial ice cover, while the most subdued response occurs in the fast ice season. During downwelling, the cold water fluxed off the shelf is able to ventilate the upper halocline of the Canada Basin. The storms approach the Beaufort Sea along three distinct pathways: a northerly route from the high Arctic, a westerly route from northern Siberia, and a southerly route from south of Bering Strait.