Shrink of an ocean gyre in the Pacific Arctic and Atlantification open a door of shadow zone

Abstract The Arctic Ocean is now facing dramatic environmental and ecosystem changes. In this context, an international multiship survey project was undertaken in 2020 to obtain current baseline data. For the first time, extremely low dissolved oxygen and acidified water were found in a fishable area of the western Arctic Ocean. The data suggested that the Beaufort Gyre shrank to the east of an ocean ridge and formed a front between the water within the gyre and the water expanded from the eastern Arctic. That phenomenon triggered a frontal northward flow that was 2–3 times faster than before. This flow could transport the low oxygen and acidified water, which had ever appeared only in the shelf-slope of the East Siberian Sea, toward the fishable area.