Distribution characteristics of pCO2 at the air-sea in the East China Sea and changes over the last 20 years

Abstract According to the carbon dioxide (pCO2), temperature (T), salinity (S) and pH of the surface seawater obtained from a survey of carbon dioxide (CO2) in the East China Sea(ECS) region from 2004 to 2023, the seasonal distribution characteristics of pCO2 in the ECS were analyzed and discussed. The results show that the overall trend of pCO2 in the ECS region indicated a slow increase followed by a decrease over the past 20 years, with the highest peak reached in 2016. The overall carbon sequestration capacity of the ECS shows a trend of first decreasing and then increasing. This is most likely related to China's adoption of more effective policies and measures in achieving carbon peak and carbon neutrality. In terms of seasonal changes, the distribution of pCO2 in the East Sea area roughly shows the differences among the offshore area. The annual seasonal changes are almost similar betweenthe continental shelf area and the outer sea area. In terms of the average distribution of pCO2 in surface seawater of the investigated area, pCO2 in autumn and summer is higher than that in winter and spring, while atmospheric pCO2 levelin spring and autumn is higher than that in summer and winter, and the seasons are all represented by the exchange of atmospheric CO2. The water system in the East Sea area is complicated, and the distribution of pCO2 in surface seawater is mainly affected by tfour major water systems: the Yangtze River, the continental shelf water, the Kuroshio water, and the coastal current of the Yellow Sea. It is generally affected by vertical mixing of water in winter and late autumn and biological activities in summer, late spring, and early autumn.