Sea ice melt drives vertical pCO2 variability modulating air–sea gas exchange

Abstract:

Strong spatial and temporal gradients in salinity, temperature, and carbonate chemistry in Arctic coastal surface waters complicate the estimation of air-sea carbon dioxide (CO2) exchange, particularly during sea ice breakup. The present study evaluates the applicability of the widely used bulk flux model under such conditions. This approach assumes homogeneous surface conditions and no vertical pCO2 gradients in the bulk seawater. However, our observations in a stratified Arctic fjord reveal pronounced vertical variability in pCO2 within the upper water column, including non-linear gradients near the air-sea interface. This results in, widely varying flux estimates depending upon the depth of the pCO2 measurement used to establish air-sea disequilibrium. Importantly, similarly structured nonlinear pCO2 profiles were observed across distinct fjord systems and years, suggesting that this vertical heterogeneity may be a characteristic feature of Arctic stratification during sea ice breakup. We recommend incorporating both micrometeorological techniques and high-resolution vertical profiling in Arctic fjords to improve flux estimates of CO2 in this rapidly changing region.

https://doi.org/10.5194/os-22-1781-2026