This study presents a new set of paired d18Osw and salinity data (n = 83) from a large region of the western Pacific (mainly the western south Pacific) collected during the 2014–2015 El Niño period. We determined regional salinity–d18Osw relationships for three ocean regions (40º–20ºN, 20ºN–30ºS, and 30º–66ºS) and found that all three regions exhibited highly linear relationships between d18Osw and salinity. The 40º–20ºN and 20ºN–30ºS regions had relatively low slopes (0.33 and 0.37 ‰ psu-1, respectively), while the 30º–66ºS region had a relatively high slope (0.54 ‰ psu-1). Each regional regression was statistically different from those of the GEOSECS (1973–1974 La Niña) data, indicating that inter-annual ENSO variability has an impact on salinity–d18Osw relationships over a wide area of the western Pacific.

Oxygen isotopes were measured at University of Toyama. Temperature and salinity were obtained by a thermosalinograph. The salinity data were corrected by an onboard Autosal salinometer (Model 8400B, Guildline Instruments Ltd.). See paper for more information.