Figure 2.

A, Sample data showing increases in CO₂ concentrations upon illumination in an assay chamber containing Prochlorococcus spp. MED4 and 2 mm C_i. That the CO₂ concentration exceeds equilibrium with HCO₃⁻ is illustrated by the addition of bovine CA just after 9 min (dashed line), which establishes equilibrium between CO₂ and HCO₃⁻. Oxygen data show that photosynthesis was not affected by the addition of bovine CA. B, A light/dark cycle with 2 mm ¹³C¹⁸O-labeled C_i added to the assay chamber (darkness = gray background; illumination at 250 μmol photons m⁻² s⁻¹ = white background).