Persistent Carbon Sink at the Ieodo Ocean Research Station in the East China Sea

 Unlike major ocean basins, the role of coastal and marginal seas as an anthropogenic CO₂ reservoir has been less studied. Using discrete surface measurements between Ieodo and Jeju Island (2015–2023) and continuous measurements at Ieodo (seasonal coverage for 2017–2019 and the year-round coverage for 2020–2023), we concluded that an increase in phytoplankton biomass from April to mid-August equalized much of the temperature-driven increase in the surface pCO₂ and thus made the Ieodo Ocean Research Station a moderate sink of CO₂. From November to March, both a large pCO₂ reduction driven by a temperature reduction and a high air–sea CO₂ exchange rate because of high windspeeds transformed the basin into a substantial CO₂ sink, yielding an annual net C uptake of 61.7 g C m^–2 yr^–1. The present study provides observational evidence for confirming a mechanism in the shallow waters of the continental shelves accumulating a significant amount of CO₂, via reinforced cooling and promoted biological CO₂ uptake, to be transported from surface waters of the basin to the interior of the adjacent East Sea deep ocean.