Near‐Surface Stratification Due to Ice Melt Biases Arctic Air‐Sea CO 2 Flux Estimates

• Published in: Geophysical Research Letters
• Main Authors: Dong, Y, Yang, M, Bakker, DCE, Liss, PS, Kitidis, V, Brown, IJ, Chierici, M, Fransson, A, Bell, TG
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU 2021
• Subjects: Arctic; Arctic Ocean; Sea ice
• Online Access: http://plymsea.ac.uk/id/eprint/9484/; http://plymsea.ac.uk/id/eprint/9484/1/2021GL095266.pdf; https://doi.org/10.1029/2021GL095266

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 (fCO2w_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 (fCO2w_surface) in the Arctic Ocean. In sea-ice melt regions, fCO2w_surface values are consistently lower than fCO2w_bulk by an average of 39 μatm. Lower fCO2w_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.