On the Pacific Ocean regime shift

The temporal variability of Pacific Ocean upper ocean heat content is exami ned for the 1948-1998 period using gridded, objectively analyzed temperatur e anomaly fields. Results indicate a "regime shift" in upper ocean temperat ure structure occurred in conjunction with the atmospheric shift in sea lev el pressure around 1975 leading to warming (cooling) in the eastern (wester n) equatorial Pacific. The shift is a basin-wide phenomenon affecting the t hermal structure from 60 degreesS to 70 degreesN. EOF analysis of the Pacif ic Ocean heat content (0-125 m.) shows a shift from a relatively cool to a warm state in the equatorial Pacific during the mid-1970s. Further analysis of the gridded temperature anomaly fields shows equatorial warming to be a s much as 1.5 degreesC and a cooling in the North Pacific of 1 degreesC, do wn to 250 meters, after the mid-1970s. Overall, the analysis indicates the "regime shift" continues through 1998 with no signs of returning to a coole r phase.