Ocean mixing is key to distribute heat and nutrients in the world oceans. Despite it’s great importance, it is mainly unconstrained even in ocean models, where numerical effects add to the deliberate parameter settings. Our novel study proposes to use the saturation state of the noble gas Argon to diagnose mixing in ocean models. We test this approach in a suite of model versions of the North Atlantic Ocean off Mauritania https://bg.copernicus.org/articles/22/1215/2025/