Rapid decline of nutrients in the subsurface of the East Sea (Japan Sea) over the past 28 years

Abstract

A previous study suggested that the Northwest Pacific Ocean has experienced an approximately 25 % decline in nutrients in the subsurface (100–850 m), leading to a 50 % decline in the surface (0–100 m) over the past four decades (Kim et al., 2022). In this study, we observed a comparable 20 % decrease in nutrients in the East/Japan Sea (EJS) subsurface (200–500 m) from 1995 to 2022, despite its limited connection to the Northwest Pacific through shallow sills (<130 m). This subsurface trend appears to contribute to a 70 % decline in nutrients in the mixed layer (0–50 m) of the eastern EJS. In contrast, complex nutrient trends were observed in the western EJS surface (0–200 m), likely influenced by anthropogenic inputs. The significant nutrient decline in the EJS, which may alter its biological production and carbon cycle, provides further evidence of regional climate regime-shift feedbacks occurring in the North Pacific and other major subtropical gyres.