Oxygen isotope fractionation in the ocean surface and ¹⁸O/ ¹⁶O of atmospheric O ₂

We have recently published a new evaluation of Earth's Dole effect, which was based, in part, on measurements of δO ₂/Ar, δ ¹⁷O and δ ¹⁸O of dissolved argon and oxygen in the ocean surface. In calculations of the oxygen isotope effect due to photosynthesis and respiration (ε _up), gross O ₂ production (G) was an important factor. However, our estimates of G were based on an approximate equation, and in a recent publication it has been suggested that G obtained with this equation could be underestimated by about 33%. If true, such underestimation of G might lead to different ε _up values. To test this possibility, we have used a new rigorous equation with relevant information on isotopic composition of photosynthetic O ₂ and recalculated ε _up. Given the uncertainties, the new values do not differ from the previous ones, and therefore, the implications of the strong fractionation in the upper ocean (∼25%) to the global Dole effect remain as in our original publication.