Freshwater and Heat Changes in the North and South Pacific Oceans between the 1960s and 1985–94

Abstract

Comparisons of hydrographic conditions in the North and South Pacific Oceans in the 1960s and 1985‐94 have been made along five World Ocean Circulation Experiment sections. Below the seasonal mixed layer, statistically significant temporal differences in salinity and temperature have been detected in the water masses that occur in the upper 2000 dbar of the water column. These water mass property differences have been used to estimate the freshwater and heat storage trends in the Pacific over the study period. Along 248N, 108N, and 178S, where either North Pacific Intermediate Water or Antarctic Intermediate Water is present, the upper waters have increased in salinity, while the intermediate and deep waters have decreased in salinity. Although the depthintegrated salinity changes observed along these sections are small, the regional redistribution of freshwater associated with the water mass changes is significant and implies significant redistribution of surface freshwater fluxes over the Pacific. Heat loss has occurred along 478N and 178S, but significant warming has occurred along 248 and 108N, giving the Pacific a net heat gain of 1.79 3 108 Jm 22. The resulting steric sea level change for the area in the Pacific between 608N and 31.58S over the roughly 20-yr study period is estimated to be a rise of 0.85 mm yr21, consistent with those in existing literature, but larger than that estimated from numerical models reported in the Intergovernmental Panel on Climate Change Second Assessment Report.