Determination Mechanisms of Oxygen Isotope Distribution in the Western Pacific and oxygen isotope ratio as potential water mass tracers

Abstract

In this study, oxygen isotope ratio (d¹⁸O_sw, n = 236) data, collected in the western Pacific Ocean in summer 2022 during the La Niña event, were used to elucidate the mechanism of determining d¹⁸O_sw distribution in the western Pacific Ocean and to examine the potential of d¹⁸O_sw data as a water mass tracer. In the 2022 La Niña event, the Intertropical Convergence Zone (ITCZ) existed between 5 and 10ºN latitude, and precipitation lowered d¹⁸O_sw. The salinity-d¹⁸O_sw relationship in the western equatorial Pacific south of 20ºN , including the ITCZ, has a larger slope and a smaller intercept (-9.56 permille) than that of the Global Seawater Oxygen-18 Database (LeGrande and Schmidt , 2006), which may reflect the atmospheric and oceanic conditions during the La Niña event. In the subtropical high-pressure zone around 20ºN and 160ºE in the western Pacific during the La Niña event, evaporation was preferential and d¹⁸O_sw was high, while the influence of high-latitude rivers was strong and d¹⁸O_sw was low in the region influenced by the Oyashio Current north of 30ºN. The d¹⁸O_sw data for the vertical samples showed that the North Pacific Intermediate Water (NPIW) is marked by d¹⁸O_sw values of -0.3 ~ -0.1 permille and can be traced to 23ºN.