This dataset contains underway surface seawater observations of O₂/Ar in the western North Pacific subtropical gyre, collected during two research cruises aboard R/V Isabu in September 2020 and September 2022. Measurements were conducted using an equilibrator inlet mass spectrometer system, with surface seawater (~7 m depth) continuously supplied via the ship's underway intake. ΔO₂/Ar anomalies were calculated as the percent deviation of the measured seawater O₂/Ar ratio from the atmospheric equilibrium ratio, indicating the degree of biological supersaturation. The dataset includes UTC, latitude, longitude, sea surface temperature (SST), salinity (SSS), and O₂/Ar (%) anomalies. These data support investigations into the interannual variability of biological productivity in oligotrophic subtropical gyres and include only surface measurements collected south of 25°N. The dataset was produced and compiled by the Hahm Laboratory at Pusan National University, South Korea. Users of this dataset are kindly requested to cite the dataset DOI and acknowledge the data authors.

This dataset has been carefully reviewed and curated in accordance with PANGAEA's exceptionally high quality standards. However, due to discontinued communication from the authors' side, it did not receive the usual formal approval by the authors and therefore lacks final scientific validation.