Presentation Information
[AAS08-P25]Spatiotemporal variations of the atmospheric O2 and CO2 over the Southern Ocean observed onboard R/V Shirase
*Daisuke Goto1, Shinji Morimoto2, Shigeyuki Ishidoya3 (1.National Institute of Polar Research, 2.Graduate School of Science, Tohoku University, 3.National Institute of Advanced Industrial Science and Technology)
Keywords:
Atmospheric oxygen,O2/N2 ratio,Southern Ocean
The atmospheric O2/N2 ratio (δ(O2/N2)) has been measured by several laboratories since the early 1990s to estimate terrestrial biospheric and oceanic CO2 uptake. These data can also provide information on air–sea O2 exchange. However, most observation sites are located on land in the Northern Hemisphere, and our understanding of the spatiotemporal variability remains limited. To improve our understanding of the spatiotemporal variations of atmospheric δ(O2/N2), we initiated continuous measurements of atmospheric δ(O2/N2) and CO2 in 2017 using the R/V Shirase, which sails between Australia and Syowa Station, Antarctica (69.00°S, 39.58°E) across the Indian Ocean sector of the Southern Ocean (Morimoto et al., 2021) where has been a data-sparse region. Observations have been conducted during the austral summers of 2017–2020, 2021–2022, and 2024–2025. During the southbound voyage in December and the northbound voyage in March, we successfully captured a latitudinal gradient in which δ(O2/N2) decreases and increases toward higher latitudes, respectively. This pattern likely reflects the seasonality of air-sea O2 exchange driven by changes in the solubility of O2 in seawater and marine biological productivity across different latitudinal zones of the Southern Ocean. In addition, elevated atmospheric δ(O2/N2) relative to the mean latitudinal distribution was observed around 50–55°S, suggesting the influence of O2 release from the ocean associated with marine biological productivity. No clear longitudinal gradient was detected during either the westbound or eastbound voyages during February–March. Such latitudinal and longitudinal δ(O2/N2) distribution data obtained over the Southern Ocean are unique, and they are expected to contribute to improvements in atmospheric transport models, ocean circulation models, and the quantification of marine biological productivity. In this presentation, we will also report the latest results obtained during the austral summer of 2025-2026.