Decadal variations of the North Pacific Tropical Water at 137°E

Abstract

The decadal variations of the North Pacific Tropical Water (NPTW) at 137°E in the western North Pacific Ocean are investigated based on the repeated hydrographic observations along with two global gridded ocean products. The results indicate that the maximum salinity of NPTW experiences significant quasi-decadal variations, having maxima around 1979, 1987, 1995, 2004, and 2012, while minima around 1974, 1983, 1991, 1999, and 2008 during the period of interest. The NPTW area also shows similar quasi-decadal variation, expanding/shrinking as its maximum salinity increases/decreases at the 137°E section. These variations are induced mainly by changes in the mixed layer salinity in the source region and large-scale circulation in the northwestern tropical Pacific Ocean, both of which are related to the Pacific Decadal Oscillation. The underlying processes at work are further confirmed through conducting the subsurface salinity budget analysis. Besides, short-term processes are also at work through nonlinear interactions, especially after 2000.