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

Dong, Y, Yang, M, Bakker, DCE, Liss, PS, Kitidis, V, Brown, IJ, Chierici, M, Fransson, A and Bell, TG 2021 Near‐Surface Stratification Due to Ice Melt Biases Arctic Air‐Sea CO 2 Flux Estimates. Geophysical Research Letters, 48 (22).

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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.

Item Type: Publication - Article
Additional Keywords: Seawater CO2 fugacity (fCO2w) vertical gradients are generated by fresh and cold sea-ice melt water, which lowers surface fCO2w • Air-sea CO2 fluxes are biased when estimated using fCO2w observations from the sub-surface (6 m depth) in sea-ice melt areas • Summertime sea-ice melt potentially results in a 6%–17% (with high uncertainty) underestimate of annual Arctic Ocean CO2 uptake
Divisions: Plymouth Marine Laboratory > National Capability categories > Long-term Multi-Centre ORCHESTRA
Plymouth Marine Laboratory > Science Areas > Marine Biochemistry and Observations
Depositing User: S Hawkins
Date made live: 14 Dec 2021 11:36
Last Modified: 14 Dec 2021 11:36

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