Parameterizing air–sea CO ₂ transfer in a macroalgal habitat and assessing its role in marine carbon dioxide removal accounting

Accurately quantifying air–sea CO 2 exchange remains a central challenge for the measurement, reporting, and verification (MRV) of marine carbon dioxide removal. I apply direct eddy covariance measurements of CO 2 fluxes at a macroalgae‐dominated coast to compile the first gas transfer velocity ( k 660 ) parameterization for such a habitat. k 660 exhibited a quadratic dependence on wind speed of the form: . Random forest analysis showed that wind speed and wind‐wave interaction control k 660 at high wind speed, and a suite of drivers enhance k 660 under calm conditions, generating a non‐zero intercept with significant impacts for CO 2 flux modelling. A simulated macroalgal marine carbon dioxide removal intervention demonstrated the sensitivity of removals to k 660 uncertainty, via its effect on CO 2 equilibration timescale, with variation across k 660 models causing shifts comparable to those by operational emissions. Finally, a new framework embedding site‐specific equilibration dynamics into marine carbon dioxide removal accounting is presented, offering an understandable and defensible tool for measurement, reporting, and verification.