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.