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

We have recently published a new evaluation of Earth's Dole effect, which was based, in part, on measurements of δ O 2 /Ar, δ 17 O and δ 18 O of dissolved argon and oxygen in the ocean surface. In calculations of the oxygen isotope effect due to photosynthesis and respiration (ɛ 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 ɛ 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 ɛ 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.