Abstract

In recent decades, the global ocean oxygen concentration has been declining, but this decline is underestimated in numerical ocean models by as much as 50%. Several mechanisms are responsible for this deoxygenation, including solubility-driven changes in surface fluxes and biological processes; however, the importance of each mechanism is unclear. By linking changes in the different processes to those driving change in temperature and dissolved inorganic carbon,  we can determine the magnitude of each driver of oxygen change. We show that a consistent oxygen decrease in the surface ocean of the North Atlantic has been dominated by an increase in biological oxygen consumption due to increased remineralisation. At its peak, biological consumption is responsible for more than 50% of the total deoxygenation and may be a cause of the mismatch between modelled and observed deoxygenation. Although the direct impact of warming is lower, deoxygenation due to solubility change has trebled in the past twenty years, suggesting it will become an increasingly significant driver of ocean deoxygenation with future warming.