Surface distributions of carbon chemistry parameters in the East China Sea in summer 2007

Abstract

Comprehensive carbon chemistry data including total alkalinity (TA), dissolved inorganic carbon (DIC), pH, fugacity of CO2, and other pertinent data (i.e., temperature, salinity, and levels of nitrate and chlorophyll a) were measured in surface waters of the East China Sea (ECS) shelf in July 2007. The results show that spatial variations in these parameters closely correspond to the distributions of various water types. The Changjiang Diluted Water (CDW) and Yellow Sea Water (YSW) areas are the two major sinks of atmospheric CO2; the Coastal Upwelling Water (CUW) area is the most important CO2 source, whereas the Kuroshio Water and Taiwan Current Warm Water areas are weak sources. The entire ECS acted as a sink for atmospheric CO2, with a flux of −2.4 to −4.3 mmol C m−2 d−1 during the study period. Identification of the CUW source area suggests that previous studies might have overestimated CO2 uptake by the ECS in summer. Our results further suggest that high biological production might be responsible for the strong sink in the CDW area but that high input of TA from the Huanghe River, which led to an elevated TA/DIC ratio, could have resulted in formation of a significant CO2 sink in the YSW area. The present data set represents the most comprehensive CO2 survey in the ECS to date and can thus be used as a baseline for monitoring future changes in the CO2 system arising from the construction of the Three Gorges Dam in the middle stretch of the Changjiang River.