Monthly and seasonal variations in the surface carbonate system and air-sea CO(2 )flux of the Yellow Sea

Abstract

Surface carbonate chemistry in the Yellow Sea was investigated based on discrete seawater samples collected from 2017 to 2020 at the Socheongcho Ocean Research Station (S-ORS; 37.423 degrees N, 124.738 degrees E). Records of carbon parameters, including seawater CO2 partial pressure (pCO2), revealed considerable seasonal variations, with amplitudes comparable to those observed across the western part of the Yellow Sea. The study site acted as a modest sink (-0.13 mol C m- 2 yr- 1) for atmospheric CO2. Biological processes (primary production and respiration) and physical conditions (temperature and degree of stratification) determined seawater pCO2, which fluctuated on an intraseasonal timescale between oversaturated and undersaturated with respect to atmospheric pCO2. Variation in pCO2 was significant in summer, depending on the biological carbon drawdown and tidal mixing-induced upwelling (increased pCO2 up to -1000 mu atm). The intraseasonal variability in seawater pCO2 may bias estimated air-sea CO2 fluxes, if measurements with a coarser (seasonal) time resolution are used.