Figure 3.

Conceptual figure for potential effect of chemical reactivity and degradation processes in the surface microlayer on concentration gradients of CO₂ (blue dashed line) in relation to assumed concentration gradients for CO₂ or CH₄ without CO₂ reactivity (solid lines in blue and red, respectively) in waters supersaturated with both CO₂ and CH₄. Please note that our intention with the figure is to present processes that contributes to the increase of apparent k₆₀₀ for CO₂ relative to CH₄, hence relating to the findings from our empirical measurements. Therefore, we chose not to include processes in the figure that have the opposite effect, i.e., enhancing apparent k₆₀₀ for CH₄, e.g., by the contribution of microbubbles or other processes that may be the result of sampling bias.