Oceanographers from the University of East Anglia (UEA) came across their finding after deploying a team of robot submarines in the Gulf of Oman.
Their collected data found a monstrous dead zone the size of the US state of Florida – and the area is unfortunately spreading.
Dead zones, or Oxygen Minimum Zones, are areas with extremely low levels of oxygen in bodies of water such as oceans and large lakes.
Dr Bastien Queste from UEA’s School of Environmental Sciences 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 meters 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.”
The scientist stressed the situation is far “worse than feared” and the zone is expanding beyond the boundaries of the Gulf of Oman.
GETTYClimate change: Scientists have warned of rapidly growing ocean dead zones
Because of the lack of oxygen all marine life in the area stands no chance of survival, leading to a catastrophic environmental disaster.
The ocean is suffocating
Dr Bastien Queste, University of East Anglia
The lack of plant life also compounds the problem by removing a crucial element in the chemical cycling of nitrogen, Dr Queste added.
The result is the increased production of nitrous oxide – a greenhouse gas 300 times more powerful than carbon dioxide.
Dr Queste said: “The ocean is suffocating.”
The researchers studied the dead zone for eight months with the help of remotely controlled underwater robots known as Seagliders.
Robot submarines were used to traverse parts of the Gulf previously inaccessible to human crews due to piracy and other geopolitical tensions.
The researchers concluded the Gulf of Oman dead zone is the largest in the world, extending almost throughout the entirety of the 165,000 square kilometres (63,700 square miles) oceanic region.
The region is home to “several high-biomass species” and as such the varying degrees of oxygen levels across the waters could have a major impact on local fisheries.
GETTYThe Gulf of Oman is currently the world's largest dead zone
GETTYDead zones are bodies of water devoid of marine life and oxygen
In their study, the scientists wrote: “Management of the fisheries and ecosystems of the western Indian Ocean over coming decades will depend crucially on better understanding and forecasting of the oxygen budget of the Gulf of Oman.”
Oceanographers first began noticing the emergence of these inhospitable zones in the 1970s, typically along coastlines where aquatic life is found in dense concentrations.
The growing problem was acknowledged by the UN Environment Programme (UNEP) in March 2004, when the first Global Environment Outlook Year Book was published.
The document concluded a total of 146 dead zones with depleted oxygen levels were spread around the world.
Klaus Toepfer, UNEP’s Executive Director, recognised the growing threat as a danger to the world’s fisheries.
He said at the time: “Some of these so-called dead zones or oxygen-starved areas are relatively small, less than one square kilometre in size, whereas others are far larger at up to 70,000 square kilometres.
“What is clear is, that unless urgent action is taken to tackle the sources of the problem, it is likely to escalate rapidly.”
A January 5, 2018, report published in the journal Science, found ocean dead zones have quadrupled in size since the 1950s.