The carbonate system in the East China Sea in winter

Abstract

Measurements of dissolved inorganic carbon (DIC), pH, total alkalinity (TA), and partial pressure of CO 2 (pCO 2) were conducted at a total of 25 stations along four cross shelf transects in the East China Sea (ECS) in January 2008. Results showed that their distributions in the surface water corresponded well to the general circulation pattern in the ECS. Low DIC and pCO 2 and high pH were found in the warm and saline Kuroshio Current water flowing northeastward along the shelf break, whereas high DIC and pCO 2 and low pH were mainly observed in the cold and less saline China Coastal Current water flowing southward along the coast of Mainland China. Difference between surface water and atmospheric pCO 2 (ΔpCO 2), ranging from ~ 0 to − 111 μatm, indicated that the entire ECS shelf acted as a CO 2 sink during winter with an average flux of CO 2 of −13.7 ± 5.7 (mmol C m − 2 day − 1 ), and is consistent with previous studies. However, pCO 2 was negatively correlated with temperature for surface waters lower than 20 °C, in contrast to the positive correlation found in the 1990s. Moreover, the wintertime ΔpCO 2 in the inner shelf near the Changjiang River estuary has appreciably decreased since the early 1990s, suggesting a decline of CO 2 sequestration capacity in this region. However, the actual causes for the observed relationship between these decadal changes and the increased eutrophication over recent decades are worth further study.