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Wednesday, May 2, 2018

Dead zone the size of Scotland extends into the Gulf of Oman

Por Rory

New research from the University of East Anglia (UEA) in Norwich, Norfolk, England, has confirmed a dramatic decrease in oxygen in the Gulf of Oman in the Arabian Sea, but the environmental disaster is worse than expected. The 'dead zone' was confirmed by underwater robots called Seagliders, which were able to collect data in previously inaccessible water areas due to piracy and geopolitical tensions.

The robots are about the same size as a small human diver, but can reach depths of 1,000 meters and travel the ocean for months, covering thousands of kilometers. Two gliders deployed in the Gulf of Oman for eight months and communicated via satellite to build an underwater image of oxygen levels and the oceanic mechanisms that transport oxygen from one area to another. Where they expected some oxygen, they found an area larger than Scotland with almost no oxygen. "The dead zones are areas devoid of oxygen, in the ocean, these are also known as 'minimum oxygen zones' and are naturally between 200 and 800 meters deep in some parts of the world," explains the director of the research, Dr. Bastien Queste, from the Faculty of Environmental Sciences of the UEA.

"They are a disaster waiting to happen, worsened by climate change, as the warmer waters contain less oxygen and fertilizers and wastewater leave the land to the seas," adds this expert, who conducted the study in collaboration with the Sultan Qaboos University of Oman. And he stresses: "The Arabian Sea is the largest and most extensive 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 hardly have data collected for almost half a century because of how difficult it is to send ships there. Our research shows that the situation is worse than feared, and that the area of the dead zone is extensive and growing. Of course, all fish, marine plants and other animals need oxygen, so they cannot survive there, it's a real environmental problem, with dire consequences for humans who depend on the oceans for food and employment," he explains.

And continues: "Another problem is that when there is no oxygen, the chemical cycle of nitrogen, a key nutrient for plant growth, changes dramatically, producing nitrous oxide, a greenhouse gas 300 times more powerful than CO2." Computer simulations of ocean oxygen show a decrease in oxygen over the next century and the growth of minimal oxygen zones. However, these simulations have difficulty representing small but very important features, such as whirlpools, that affect the way oxygen is transported. The team combined its Seaglider data with a very high resolution computer simulation to determine how oxygen is distributed in the northwestern Arabian Sea throughout the different seasons and monsoons and found that the dead zone moves up and down between seasons, which cause the fish to squeeze into a thin layer near the surface. "The management of fisheries and ecosystems of the western Indian Ocean over the next few decades will depend on a better understanding and forecast of oxygen levels in key areas such as the Gulf of Oman," Queste says. The next step of the experts is to perform a deeper dive to better determine the causes of the growth of dead zones.