CO2 uptake in the East China Sea relying on Changjiang runoff is prone to change

Limited knowledge exists concerning the unusually large CO2 uptake capacity in the East China Sea (ECS), which is the eminent continental shelf pump for efficient transfer of atmospheric CO2 to the deep ocean. Here we show evidence of strong control of river runoff on the CO2uptake capacity of the ECS. From 8‐years of observations in the productive ECS shelf, we present the first dataset to show the complete seasonal cycle of CO2 flux, which gives an annual flux of 2.3 ± 0.4 mol C m−2 y−1 as a net sink of atmospheric CO2. Further, we found biological sequestration of CO2 taking place in the highly productive Changjiang river plume in warm seasons due to the riverine nutrient enrichment. Consequently, changes in the plume area due to changes in the Changjiang River Discharge (referred to as the Discharge hereafter) strongly affect the CO2 uptake capacity. As the Discharge may decrease due to the Three Gorges Dam operation, the Changjiang plume will probably also decrease, resulting in reduction in CO2 uptake capacity and even a shift from a CO2 sink to a source. Key Points Strong control of river runoff on the CO2 uptake capacity change in ECS The threat of the ECS shifting from a sink of atmospheric CO2 to a source Changjiang discharge decreases, resulting in the ECS CO2 uptake reduction