资源环境科技发展态势分析平台

Air-sea carbon dioxide (CO₂) flux is generally estimated by the bulk method using upper ocean CO₂ fugacity measurements. In the summertime Arctic, sea-ice melt results in stratification within the upper ocean (top ∼10 m), which can bias bulk CO₂ flux estimates when the seawater CO₂ fugacity is taken from a ship’s seawater inlet at ∼6 m depth (fCO_{2w_bulk}). Direct flux measurements by eddy covariance are unaffected by near-surface stratification. We use eddy covariance CO₂ flux measurements to infer sea surface CO₂ fugacity (fCO_{2w_surface}) in the Arctic Ocean. In sea-ice melt regions, fCO_{2w_surface} values are consistently lower than fCO_{2w_bulk} by an average of 39 µatm. Lower fCO_{2w_surface} can be partially accounted for by fresher (≥ 27%) and colder (17%) melt waters. A back-of-the-envelope calculation shows that neglecting the summertime sea-ice melt could lead to a 6–17% underestimate of the annual Arctic Ocean CO₂ uptake.