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

We analyzed nitrogen isotopic ratio (delta N-15) of settling particles at four sites in the western and central equatorial Pacific from January to November 1999, together with the delta N-15 of nitrate above 200 m depth in December 1999. The delta N-15 values of settling particles at the two western sites (station 1 and 2) were about 3.0 parts per thousand more depleted than that at the most eastern site (station 9). In March 1999, the delta N-15 values rose from 3.7 parts per thousand to 7.2 parts per thousand at station 3 located at 0 degrees N 145 degrees 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 delta N-15 of nitrate in surface water suggested that the depleted delta N-15 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 delta N-15 values of settling particles.