Long-term hydrographic variability in the Northwest Pacific Ocean

[1] Hydrographic changes in the Northwest Pacific Ocean are examined using data for two time periods: 1945: 1975 and 1976:1998. The largest changes in T/S (2°C,0.2 psu) are within the interfrontal zone between the Kuroshio Extension (KE) and the subarctic (or Oyashio) front near the Shatsky Rise, and are consistent with a southward shift of the Kuroshio Bifurcation Front (KBF). Other major changes seen are a freshening of ∼0.04 psu of the newly formed North Pacific Intermediate Water (NPIW); a shoaling over time of the halocline in the center of the Western Subarctic Gyre (WSAG); and a southward shift of the subarctic front between the dateline and 150°W. Because long-term T/S changes near the Shatsky Rise are well-correlated, we have examined subsurface thermal data at 100 and 200-m depth in the region and found that shifts in front locations show a high degree of correlation with the PDO index on an interannual basis, and lagging it by ∼1 year at 200-m depth.