Oxygen is fundamental to ocean biogeochemical processes, with deoxygenation potentially reducing biodiversity, and disrupting biogeochemical cycles. This paper develops and implements a new inverse method to decompose oxygen change into its constituent parts by linking each process to concomitant changes in temperature and dissolved inorganic carbon (DIC). They apply this method to a GO-SHIP repeated section of the North Atlantic Ocean. They find that alterations in remineralisation, either local or upstream, are responsible for up to half of the total oxygen decrease seen in the upper 2000 m between 1992 and 2015. This method could be repeated on any dataset, observations or model, that includes temperature, DIC, and oxygen concentration data.