pCO2 distribution and CO2 flux on the inner continental shelf of the East China Sea during summer 2011

Measurements of pH, total alkalinity (TA), partial pressure of CO₂ (pCO₂) and air-sea CO₂ flux (FCO₂) were conducted for the inner continental shelf of the East China Sea (ECS) during August 2011. Variations in pCO₂ distribution and FCO₂ magnitude during the construction of the Three Gorges Dam (TGD) (2003–2009), and the potential effects of the TGD on the air-sea CO₂ exchange were examined. Results showed that the ECS acts as an overall CO₂ sink during summer, with pCO₂ ranging from 107 to 585 μatm and an average FCO₂ of ?6.39 mmol/(m² ·d). Low pCO₂ (<350 μatm) levels were observed at the central shelf (28°-32°N, 123°-125.5°E) where most CO₂-absorption occurred. High pCO₂ (>420 μatm) levels were found in the Changjiang estuary and Hangzhou Bay which acted as the main CO₂ source. A negative relationship between pCO₂ and salinity (R ²=0.722 0) in the estuary zone indicated the predominant effect of the Changjiang Diluted Water (CDW) on the seawater CO₂ system, whereas a positive relationship (R ²=0.744 8) in the offshore zone revealed the influence of the Taiwan Current Warm Water (TCWW). Together with the historical data, our results indicated that the CO₂ sink has shown a shift southwest while FCO₂ exhibited dramatic fluctuation during the construction of the TGD, which is located in the middle reaches of the Changjiang. These variations probably reflect fluctuation in the Changjiang runoff, nutrient import, phytoplankton productivity, and sediment input, which are likely to have been caused by the operations of the TGD. Nevertheless, the potential influence of the TGD on the CO₂ flux in the ECS is worthy of further study.