A committed fourfold increase in ocean oxygen loss

Less than a quarter of ocean deoxygenation that will ultimately be caused by historical CO₂ emissions is already realized, according to millennial-scale model simulations that assume zero CO₂ emissions from year 2021 onwards. About 80% of the committed oxygen loss occurs below 2000 m depth, where a more sluggish overturning circulation will increase water residence times and accumulation of respiratory oxygen demand. According to the model results, the deep ocean will thereby lose more than 10% of its pre-industrial oxygen content even if CO₂ emissions and thus global warming were stopped today. In the surface layer, however, the ongoing deoxygenation will largely stop once CO₂ emissions are stopped. Accounting for the joint effects of committed oxygen loss and ocean warming, metabolic viability representative for marine animals declines by up to 25% over large regions of the deep ocean, posing an unavoidable escalation of anthropogenic pressure on deep-ocean ecosystems.