Observations of a Kenai Eddy and a Sitka Eddy in the Northern Gulf of Alaska

Mesoscale eddies in the Gulf of Alaska are thought to contribute to the shelf-slope exchange of nutrients and plankton, enhancing biological production. We report on a study of two anticyclonic mesoscale eddies in this region observed through in situ sampling during August and September 2007. Both eddies exhibited in their cores q-S profiles with warmer, fresher water relative to the properties of the ambient basin water between 150-and 300-m depths. Hydrographic properties and satellite altimetry data were analyzed to identify likely formation regions for each feature. One eddy, sampled near Yakutat, Alaska, originated in the Sitka formation region (221-223 degrees E); the second eddy, sampled south of Kodiak Island, originated near the Kenai Peninsula, southeast of the Kennedy and Stevenson entrances to Cook Inlet, an area not previously studied as a formation region. Subsequent analysis of 16 years of satellite altimeter data (from 1992 to 2008) with an algorithm designed to identify and track eddies revealed approximately six Kenai eddies that have formed in this region. Although this number constitutes only 3.2% of the 188 eddies identified by the algorithm during this period, it represents 15.4% of the 39 eddies that formed in or propagated westward into the Alaskan Stream.