Near-surface stratification due to ice melt biases Arctic air-sea CO2 flux estimates
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...
Published in: | Geophysical Research Letters |
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Main Authors: | , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
2021
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Subjects: | |
Online Access: | https://ueaeprints.uea.ac.uk/id/eprint/82091/ https://ueaeprints.uea.ac.uk/id/eprint/82091/1/Accepted_Manuscript.pdf https://doi.org/10.1029/2021GL095266 |
Summary: | 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. |
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