Anthropogenic carbon dioxide emissions could strip tropical oceans of oxygen and drastically expand the region's 'dead zones' by the end of this century. Large portions of the tropical oceans are oxygen-depleted and hostile to marine life. Although these poorly ventilated zones are known to be highly sensitive to climate change, it's not clear how they will fare over the next century.
Andreas Oschlies at the University of Kiel, Germany, and colleagues used a global biogeochemical model to examine the effect of rising atmospheric carbon dioxide concentrations on the oxygen content of the world's oceans. They found that emissions-stimulated increases in the carbon content of marine biological matter might deplete oxygen in tropical oceans, with the greatest oxygen losses — of up to 70 per cent by 2100 — occurring on the margins of existing dead zones. Overall, the model predicts a 50 per cent increase in the volume of oxygen-depleted water in the tropical oceans by the end of the century.
The researchers attribute the spreading tropical dead zones to greater bacterial activity, which consumes oxygen, in a high-carbon world where organic carbon — the fodder of marine life — is in plentiful supply.