9 May 2022
The Oyashio transport off Hokkaido decreased remarkably during the past decades (1993– 2011), caused by the frequent appearance of clockwise warm eddies originating in the Kuroshio, and the decrease was probably linked with the recent northward shift of the gyre boundary associated with the interdecadal weakening of the Aleutian Low (Kuroda et al. [...] Monitoring the changes in the physical and biogeochemical variables such as O2 for the extended period is a key to understand the linkage between decadal to longer-term variations in the circulations of the atmosphere and the ocean and their impacts on the O2 content of the ocean. [...] Clarifying the changes in O2 in the OSMW and in the WSAW, respectively, are also very important to understand the cause of long-term O2 decrease in the Oyashio and the subarctic North Pacific in more detail. [...] From January to March, the Cold winter- spring community appears in the northern areas and the Transition community appears in the southern areas, and the Warm community appears in the most southern areas. [...] In May, the Cold spring-summer community mainly appeared in the northern areas, the Transition community appears in the southern areas, and the Warm community appears in the most southern areas.