Global Warming

Global warming could enlarge world’s largest ocean dead zone

Climate modelling experts ran computer experiments to predict how the world’s largest oxygen minimum zone (OMZ), situated in the Arabian Sea, will react to future warming scenarios.1 First documented in the 1960s, the dimensions of the Arabian Sea’s dead zone, an area the size of Scotland, were only formally established a year ago by marine biologists who dispatched underwater robots.

The most recent simulation, led by Zouhair Lachkar from New York University Abu Dhabi’s Center for Prototype Climate Modelling, showed that an additional warming of 2°C to 4°C is bound to intensify the OMZ. This will further reduce marine habitats for fish species intolerant to hypoxic conditions, strain commercially important fisheries, and accelerate the release of toxic heat-trapping gas into the atmosphere.

Naturally occurring oxygen minimum zones exist in three other locations worldwide. They result from an imbalance between oxygen supply and loss. In any water body, atmospheric oxygen is injected and mixed by waves and eddies, and consumed by bacteria feeding on sinking and decomposing organic matter. Because the Arabian Sea is one of the most productive marine ecosystems, it generates large amounts of organic matter that is decomposed by bacteria, tipping the fragile oxygen balance towards anoxia.

The intensification of the oxygen minimum zone, especially nearer the surface, has huge impacts for local communities. When the low oxygen boundary gets shallower, fish communities are squeezed into a thinner layer. This puts a lot of stress on fisheries.