Transition of low-salinity water in the Western Pacific Warm Pool recorded in the nitrogen isotopic ratios of settling particles

Abstract

We analyzed nitrogen isotopic ratio (δ15N) of settling particles at four sites in the western and central equatorial Pacific from January to November 1999, together with the δ15N of nitrate above 200 in depth in December 1999. The δ 15N values of settling particles at the two western sites (station 1 and 2) were about 3.0 %o more depleted than that at the most eastern site (station 9). In March 1999, the δ15N values rose from 3.7 ‰ to 7.2 ‰ at station 3 located at 0°N 145°E. During this month, the salinity at this site also increased by 0.4 psu, suggesting that low-salinity water had shifted to the west. The relationship between salinity and δ15N of nitrate in surface water suggested that the depleted δ 15N reflects river discharge, atmospheric deposition and/or nitrogen fixation. Thus, we were able to reconstruct the transition of low-salinity water in the WPWP based on the δ 15N values of settling particles. Copyright 2005 by the American Geophysical Union.