The Subsurface Boundary Between Subarctic Pacific Water and Pacific Equatorial, Water in the Transition Zone Off Southern California

Correlations of temperature with salinity and of temperature with oxygen demonstrated that in summer 1955, between southern California and Hawaii, there was an abrupt transition from Subarctic Pacific Water to a modified Pacific Equatorial at depths where thermosteric anomalies vary between 125 and 70 centiliters per metric ton. Between 125° and 140° W long the transition (a weak east‐west frontal zone) was well defined at about 26.5° N lat. East of 125° W, the front was not well defined. The oxygen minimum zones were found at different depths and at different thermosteric anomaly surfaces on either side of the transition. The oxygen minimum for Subarctic Pacific Water was about 200 m deeper than that of the water from the south. The two oxygen minimum zones were clearly separated by an “enriched” zone of dissolved oxygen which we take as evidence of vertical mixing. Vertical mixing was most strongly indicated nearshore in the vicinity of Point Conception. The boundary has a slope, with Subarctic Pacific Water overriding the southern water. The velocity difference across the boundary using the Margules‐Witte equation is 4 cm/sec cyclonically.