The Southern Ocean plays a critical role in regulating the global biogeochemical cycle and the atmospheric CO₂ level. The influx of CO₂ into the deep ocean is enhanced by the biological pump through photosynthesis, which also produces organic matters sinking to the deep ocean for carbon storage on a longer time scale. The primary productivity or biological oxygen production of the Southern Ocean is mainly controlled by the availability of iron. Previous studies observed a decreasing trend of oxygen productions from low latitude to high latitude towards Antarctica. This is caused by the decreasing fluxes of iron from land to the Southern Ocean. In this study, we estimate the net and gross oxygen production rate of the Cosmonaut Sea based on O₂/Ar ratios and a triple oxygen isotope approach (δ¹⁸O, ¹⁷Δ). We analyzed the O₂/Ar ratios and triple oxygen isotope compositions of dissolved oxygen collected from the Cosmonaut sea in January, 2021. Averaged net and gross O₂ production rate are 12.9 and 133 mmol O₂ m^-2 day^-1, respectively. Not a latitudinal trend, but a longitudinal increasing trend in O₂ production rate from west to east was observed. This trend is associated with the strength of the iron-rich Upper Circumpolar Deep Water (UCDW). We identified the UCDW by the maximum temperature of the water column (T_max) and observed increasing O₂ production rate with increasing T_max. Our observation indicates that the vertical mixing and upwelling of UCDW enhances primary productivity in the Cosmonaut Sea.
 

gross primary productivity, Southern Ocean, triple oxygen isotope, dissolved oxygen