Macroalgal beds are among the vegetated coastal ecosystems that take up atmospheric CO₂. We investigated the relationships between macroalgal metabolism and inorganic and organic carbon fluxes in a temperate macroalgal bed during the productive time of year. The macroalgal metabolism formed water with low CO₂ and high dissolved organic carbon concentrations that was then exported offshore. This export process potentially enhances CO₂ uptake in and around macroalgal beds.