Beaufort shelf break eddies and shelf-basin exchange of Pacific summer water in the western Arctic Ocean detected by satellite and modeling analyses

Mesoscale eddies and shelf-basin exchange of Pacific summer water in the western Arctic Ocean are examined using satellite data sets and an eddy-resolving coupled sea ice-ocean model. Several surface eddy-like features along the Beaufort shelf break are detected by the Moderate-Resolution Imaging Spectroradiometer (MODIS) sea surface temperature and the Global Imager (GLI) radiance image. The QuikSCAT sea wind vectors indicate that summertime shelf-wide wind is an important factor for interannual variations in the eddy properties. A realistic numerical experiment reveals that the origin of shelf break warm eddies and timing of their generation can be classified into three types. Type I eddies are frequently produced in the vicinity of the Barrow Canyon throughout the summer season by a combination of outflow of Pacific summer water with a low potential vorticity from the Barrow Canyon and lateral velocity shear of the canyon jet. Surface wind variability modulates the timing of generation. Type II and Type III eddies originate from an eastward current along the Beaufort shelf break, although origin depth and background hydrographic structure differ between them. Type II eddies are spawned from the shelf slope at middepth during early summer. Type III eddies are generated from the surface isopycnal front over the shelf break during late summer. The shift from Type II eddies to Type III eddies is caused by surface buoyancy input in the upstream region. A sensitivity experiment using different atmospheric forcing data suggest that the mechanism controlling Pacific water transport from the Chukchi shelf to the Canada Basin differs depending on surface wind fields in the shelf region. The mesoscale eddies primarily induce the shelf-to-basin transport under weak or westerly wind conditions during summer, while wind-driven Ekman transport is a major driver in the easterly wind regime. Year 2003 (2007) corresponds to the former (latter) case.