Surface partial pressure of CO2 and air–sea exchange in the northern Yellow Sea

Abstract

We report sea surface partial pressure of CO2 (pCO2) and air–sea exchange in the northern Yellow Sea (NYS, 37–40°N to 121–124°E) for the first time, based on data collected during four cruises covering all seasons from 2006 to 2007. Sea surface pCO2 showed large seasonal and spatial variations, with the highest values observed in summer and the lowest in winter. During summer and winter, the pCO2 distribution in most parts of the study area was strongly influenced by sea surface temperature, while biological processes played an important role during fall and spring. In addition, other processes also contributed to the pCO2 variations, such as the seasonally varying vertical structure of the water column (vertical mixing and stratification), intrusion of the Yellow Sea Warm Current during winter, river inputs, upwelling of cold bottom waters, and resuspension of sediments from the Huanghe (a.k.a., Yellow River). However, sea surface temperature generally played a more important role in the annual cycle of pCO2 than biological processes in most parts of the study area. Air–sea CO2 flux computations indicated that the NYS acted as a net CO2 source with respect to the atmosphere in each season, annually releasing 0.63±0.10molCm−2 to the atmosphere. In combination with the CO2 efflux rate (1.68±0.33molCm−2yr−1) reported in the southern Yellow Sea (SYS), we estimate that the entire Yellow Sea, including both the NYS and the SYS, was a net CO2 source at a rate of ~1.49molCm−2yr−1, annually releasing ~6.78Tg C to the atmosphere (1Tg=1012g).