Zonal evolution of Alaskan Stream structure and transport quantified with Argo data. Issue 2 (1st February 2017)

• Record Type: Journal Article
• Authors: Logan, Paige D.; Johnson, Gregory C.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 2(2017)
• Page Start: 821
• Page End: 833
• Publication Date: 2017-02-01
• Subjects: Alaskan Stream -- Argo -- western boundary current -- pacific equatorial water -- volume transport; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/2016JC012302
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The Alaskan Stream (AS) flows west‐southwestward along the south side of Alaska and the Aleutian Island Arc; a western boundary current at the northern edge of the North Pacific subpolar gyre. The Argo float array has improved sampling of the Gulf of Alaska, allowing quantification of the AS's zonal evolution from 140°W to 175°W. Geostrophic alongshore transport of the AS in the upper 1000 dbar referenced to an assumed level of no motion at 1000 dbar shows little change from east to west. However, alongshore absolute geostrophic transports in the top 2000 dbar (obtained by combining mean absolute 1000‐dbar velocities from float displacements with the geostrophic velocity fields) generally increase to the west. We estimate full‐depth transports by fitting a barotropic and the first two baroclinic modes calculated from a climatology to the absolute geostrophic velocities in the upper 2000 dbar and applying the velocities from these fits from 2000 dbar to the seafloor. Flowing west from its formation region at 140°W–145°W the full‐depth AS becomes stronger, more barotropic, and also narrower once it reaches ∼160°W, with along‐shore transports increasing from −16.4 ± 4.9 Sv (1 Sv = 10 6 m 3 s −1 ) at 140°W to −32.6 ± 5.2 Sv at 175°W. Mean concentrations of relatively warm, salty, oxygen‐poor, and nutrient‐rich Pacific Equatorial Water (PEW) in the AS decrease from 17.8% ± 0.3% to 8.5% ± 0.5% between 140°W and 175°W. However, the volume transport of PEW by the AS exhibits little change over the PEW density range between these longitudes. Key Points: The Alaskan Stream strengthens as it flows westward with full‐depth volume transports increasing from 16 Sv at 140°W to 33 Sv at 175°W The high‐velocity core of the Alaskan Stream becomes more barotropic and narrower as it flows westward Pacific Equatorial Water (PEW) concentration in the Alaskan Stream decreases westward but its volume transport stays fairly constant