Oral or Poster

IAPSO

JPM02 - Ocean dynamics and climate variability in the North Pacific

Interannual variabilities of temperature and salinity in the southwestern Okhotsk Sea with its relation to the Japan Sea over the past 40 years

The Soya Warm Current (SWC) is part of the Japan Sea Throughflow (JSTF) and flows into the Okhotsk Sea through the Soya Strait. The SWC is driven by the sea level difference between the Japan Sea and the Okhotsk Sea. The current speed and volume transport of the SWC are strong in summer and weak in winter. The SWC supplies heat and salt into the Sea of Okhotsk and affects the coastal environment and biological productivity. Hydrological climatology in this region has been established in previous studies (Itoh and Ohshima, 2000; Ohshima et al., 2017). However, the interannual variations of temperature and salinity in the SWC region have not been examined. In this study, we created the updated monthly climatology of temperature and salinity based on accumulated observational data and a new mapping method by Mensah and Ohshima (2023). This method reflects that the current flows along isobaths under the conservation of potential vorticity, which is suitable for the coastally trapped SWC. Using this climatology, we estimated the interannual variabilities of temperature and salinity in the southwestern part of the Okhotsk Sea, influenced both by the SWC and sea ice. We defined the SWC region as the coastal area whose bottom depth is shallower than 120 m. According to the timeseries of the anomalies, the temperature, salinity, and volume transport have strong correlation with each other, suggesting that these variations originate from the inflow of the SWC. Regarding the long-term variations, the significant warming trend of 1.5 �� is identified in the SWC region over the period of 1980-2023. This warming trend was most pronounced at 30 m depth, which suggests that the warming is not due to local interaction with atmosphere but due to the change in the origin water from the Japan Sea. To investigate the relationships between the SWC and the JSTF, we conducted the correlation analysis by incorporating additional datasets of the atmospheric conditions. The results indicate that the timeseries of temperature in the SWC region exhibits a positive correlation with the sea surface temperature in the coastal area of the Japan Sea. Apart from the warming trend in the SWC region, surface layer salinity just offshore of the SWC has decreased mainly in autumn. This salinity decrease suggests changes in the discharge of the Amur River and in the southward current along the Sakhalin shelf.