Habitable Japan Sustainability of atmospheric and oceanic environment as a survival basis of island country Japan Grant-in-Aid for Transformative Research Areas (A) (2024–2028)

In the Sea of Japan, water temperatures had increased rapidly and maintained their high temperature after 2019. During the same period, poor catches of Japanese common squid and non-appearance of large jellyfish have continued, while an increase of snow crab stocks has been reported. Although it is speculated that the distribution of fishery resources in the Japan Sea has changed drastically along with the drastic changes in the marine environment, no clear answer has been provided at all.

On the other hand, after 2019, a warm water area had generated (1 in the figure) east of Oki Islands in 2019 and lasted for until 2023. This warm water area is suggested to shift the main axis of the Tsushima Warm Current flowing in the vicinity offshore; it is highly likely that the offshore shift of the Tsushima Warm Current (TWC) occurred after 2019.

This study is attempting to show following processes: an offshore shift of the TWC due to the warm eddy (2 in the figure) which created a stagnation zone in the coastal area of Honshu in the Japan Sea; this situation preventing the entry of marine resource recruitment originating outside the stagnation zone and possibly retaining marine resources originating inside the stagnation zone (3 in the figure) In addition, we discuss the relationship between the generation of the warm water eddy off the east coast of Oki, volume transport fluctuation of the TWC and large meander of Kuroshio(0 and -1 in the figure). The possibility that the simultaneous occurrence of the TWC and Kuroshio meandering may cause a drastic change in the distribution of fishery resources around Japan is also explored.