Water Mass Structure of Warm and Cold Anticyclonic Eddies in the Western Boundary Region of the Subarctic North Pacific

Vertical profile data of temperature and salinity from various sources were analyzed together with satellite altimeter data to investigate the water mass characteristics of warm and cold anticyclonic eddies in the western boundaryregionof the subarctic North Pacific.A densedistributionof anticyclonic eddieswith warm and saline core water occurred near the Kuroshio Extension, and the distribution extends northward‐ northeastward into the western subarctic gyre along the Japan and Kuril‐Kamchatka trenches. Eddies with cold and fresh core water are found mainly around the Oyashio southward intrusions and farther north near the Kuril Islands. Based on the heat content anomaly integrated over 50‐200 dbar, 85% of the anticyclonic eddies within the study area (358‐508N, 1408‐1558E) have a warm and saline core and 15% have a cold and fresh core. Warm and saline eddies around the Japan and Kuril‐Kamchatka trenches have a double-core structure, with a cold and freshwater mass located below the warm core. The northward propagation of these eddies along the trench line results in a large northward heat (salinity) transport in the upper 400 dbar (250 dbar) and a negative salinity transport below 350 dbar. The lower core water is colder and fresher on isopycnal surfaces at around 26.70sucompared with the climatology.Given that the 26.70su isopycnal surface does not outcrop in the open North Pacific, an alignment process is suggested to occur between the warm and saline and the cold and fresh anticyclonic eddies in the upper and intermediate layers, respectively.

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