Contribution of Changjiang River discharge to CO2 uptake capacity of the northern East China Sea in August 2016

Abstract

Despite the known significant effect of the Changjiang River on the surface fugacity of CO2 (fCO2) in the northern East China Sea (ECS) during summer, the influence of the river on CO2 uptake capacity has yet to be quantified. In this study, spatial variation in surface fCO2 was studied in the northern ECS in August 2016. The controlling factors on surface fCO2 were identified and quantified. Surface fCO2, as influenced by the Changjiang River, was up to 250 μatm lower than that of oceanic surface water. Biological activity in the river-influenced region lowered surface fCO2 150 μatm–300 μatm below the physical mixing line of oceanic water with low-salinity and high-CO2 Changjiang River water and contributed to CO2 drawdown. The northern ECS was a CO2 sink for the atmosphere, with an average CO2 flux of −6.74 ± 2.89 mmol C m−2 d−1. The CO2 uptake capacity was correlated with salinity, implying an importance of northeastward extension of Changjiang River plume, not the amount of the discharge.