The crucial contribution of mixing to present and future ocean oxygen distribution

The oxygen content of the ocean interior largely results from a balance between respiration and advective ventilation, with only a small contribution from mixing processes. However, two important characteristics, which are key to future oxygen distribution in the ocean, primarily depend on the strength of ocean mixing. The first relates to the oxygen minimum zones (OMZ), which are wide O₂-deficient mesopelagic layers inhospitable to most marine macro-fauna. We illustrate how mixing intensity controls the volume of all major OMZs. The second relates to one of the most worrying responses of the ocean to climate change: deoxygenation, including in OMZs. Several observational and model studies show that reduction in oxygen mixing plays a dominant role in global deoxygenation. Uncertainties in the representation of mixing in Earth system models and difficulties to measure mixing rates in the field hinder our ability to project the future evolution of OMZs.