The isotopic ratio 18 O/ 16 O of dissolved O 2 in aquatic systems is affected by the preferential biological uptake of 16 O ( ε ). Studies over the past six decades reveal that during incubation experiments, the isotopic effect of microorganism respiration ( ε organism ) varies in the range of −18‰ to −22‰. In contrast, natural variations in the deep‐ocean O 2 concentration and δ 18 O levels show a considerably weaker effect (...

The isotopic composition of dissolved O 2 (δ 18 O) in aquatic environments is strongly affected by the preferential uptake of the lighter isotopologue during biological consumption processes. Numerous studies have shown that during incubation experiments, the isotopic effect of microorganism respiration ( ε organism ) is on the order of −20‰. However, studies of the co‐variations of O 2 and δ 18 O in natural environments show...