[A-CG44] Kuroshio Large Meander

[ACG44-P03] Transition of the Kuroshio Large Meander Path and its Impact on the Seto Inland Sea

*Toru Miyama¹, Yasumasa Miyazawa¹, Naoki Yoshie², Xinyu Guo² (1.Japan Agency for Marine-Earth Science and Technology, Application Laboratory, 2.Ehime University)

Keywords:Kuroshio Large Meander, Seto Island Sea, Bungo Channel

Kuroshio Large Meander, which significantly changes the flow path of the Kuroshio Current, alters the distribution of flow velocity, temperature, nutrients, etc., and has a significant impact on the ecosystem of Japan's southern coast. The Kuroshio Large Meander, which began in 2017 and has lasted more than six and half years, requires understanding its impacts. The Kuroshio Large Meander since 2017 has been characterized, starting around 2019, by an untypical path (based on the earlier period and the 2004-2005 period), the cold-water eddy shifted westward. During a typical Kuroshio meander, the flow path of the Kuroshio approaches Cape Ashizuri and leaves at the Kii Peninsula, which is thought to increase the flow through the Seto Inland Sea, which flows in from the Bungo Channel and exits the Kii Channel (Komai et al. 2008, Hayashida et al. 2023). However, during the Kuroshio Large Meander beginning around 2019, the cold-water eddy often increased its separation from Cape Ashizuri due to its westward shift, resulting in a different impact on the Seto Inland Sea than it had before. Such a flow path is a unique situation observed only during the period 1975-1980 in other large meander period (Miyama et al. 2023). To investigate the effects of the Kuroshio meander on flow path changes, we used JCOPE2M reanalysis data from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), which has daily average data with a horizontal resolution of 1/12 degree around Japan from 1993 to the present. Using this data as a monthly average, we analyzed the time series of inflow into the Bungo Channel, which revealed a decrease in inflow into the Bungo Channel beginning around 2019, which was not seen before that time. According to the observation-based data, the Kuroshio has been leaving at Cape Ashizuri more frequently after 2019 than before, and the change in inflow is closely related to the change in the Kuroshio's flow path. This decrease in inflow has the potential to affect the ecosystem of the Seto Inland Sea. For example, it has been pointed out that the occurrence of the red tide in the Bungo Channel in 2020 was the slowest in recorded history and did not occur until autumn, possibly because the Kuroshio left the Bungo Channel, weakening the inflow and preventing a rise in water temperature.