Growing ‘dead zone’ in Gulf of Oman

Dr Queste said, “Dead zones are areas devoid of oxygen. In the ocean, these are also known as ‘oxygen minimum zones’ and they are naturally occurring between 200 and 800 metres deep in some parts of the world.

“They are a disaster waiting to happen — made worse by climate change, as warmer waters hold less oxygen, and by fertiliser and sewage running off the land into the seas.

“The Arabian Sea is the largest and thickest dead zone in the world. But until now, no one really knew how bad the situation was because piracy and conflicts in the area have made it too dangerous to collect data.

“We barely have any data collected for almost half a century because of how difficult it is to send ships there. Our research shows that the situation is actually worse than feared — and that the area of dead zone is vast and growing. The ocean is suffocating.

“Of course all fish, marine plants and other animals need oxygen, so they can’t survive there. It’s a real environmental problem, with dire consequences for humans too who rely on the oceans for food and employment.

“Another problem is that when oxygen is absent, the chemical cycling of nitrogen — a key nutrient for plant growth — changes dramatically. Nitrous oxide, a greenhouse gas 300 times more potent than CO2 is produced,” he added.

Computer simulations of ocean oxygen show a decrease in oxygen over the next century and growing oxygen minimum zones.

However, these simulations have a difficult time representing small but very important features such as eddies which impact how oxygen is transported.

The team combined their Seaglider data with a very highresolution computer simulation to determine how oxygen is spread around the north-western Arabian Sea throughout different seasons and the monsoons.

They found that the dead zone moves up and down between seasons, causing fish to be squeezed in a thin layer near the surface.

“Management of the fisheries and ecosystems of the western Indian Ocean over the coming decades will depend on better understanding and forecasting of oxygen levels in key areas such as the Gulf of Oman,” added Dr Queste.