World's largest 'dead zone' in Gulf of Oman has dramatically grown - but the tide can still be turned
'It’s an insidious process and you don’t notice it until it’s too late' says Dr Bastien Queste, who warns fish and marine life cannot survive in such conditions
Action could still help to prevent potentially “catastrophic” harm to the seas in the Gulf region, a researcher has said after releasing a study indicating that a local oceanic “dead zone” has dramatically increased in size.
Data from unmanned vehicles deployed in the Gulf of Oman has found that the Arabian Sea oxygen minimum zone (OMZ) has grown significantly as a result of climate change and, possibly, pollution.
The study is the first in decades to comprehensively measure oxygen levels in the Gulf of Oman, which sits between the Arabian Sea and the Strait of Hormuz.
“The take-home message is that standing on the beach looking out, the sea will look identical. You’re not going to notice the impact straight away, but things are changing incredibly rapidly and dangerously,” the study’s lead author, Dr Bastien Queste, a research fellow in the School of Environmental Sciences at the University of East Anglia in Norwich, told The National on Thursday.
“It’s an insidious process and you don’t notice it until it’s too late. In the same way we have to think about climate change, we have to be conscious of what we do and reduce waste and pollution as much as possible and, if we can, reverse it.
“Especially for the countries like the Gulf states that depend on the sea for desalination or tourism, it’s an incredibly valuable and precious resource and spoiling it would be catastrophic.”
Climate change is thought to be the key reason behind the expansion of the Arabian Sea OMZ.
Warmer temperatures cause bacteria to respire more, depleting oxygen supplies, while warmer surface layers reduce the vertical mixing of the water, cutting the amount of oxygen that gets absorbed. The effect of climate change on wind patterns, which also affect mixing, may also play a role.
Another factor may be pollution, as it increases the levels of certain nutrients, which causes more algal growth and, in turn, increases the amount of bacterial activity.
The area that had been expected to contain oxygen, but which was found to be almost totally depleted of it, is larger than Scotland.
The low levels of oxygen make it impossible for many types of creature to survive, potentially having knock-on effects up the food chain. At certain times of the year, fish can be stuck in a narrower layer near the surface.
The Arabian Sea OMZ is the largest and thickest of a number of naturally occurring OMZs around the world. They are caused by the upwelling of nutrient-rich waters that cause microscopic plants called phytoplankton to grow. When this organic matter decays, a process called remineralisation uses up the water’s oxygen.
Dr Queste said that each OMZ exists in a delicate balance, so that modest changes can have significant impacts. In the Gulf of Oman’s case, the margins around the OMZ are experiencing what Dr Queste described as “very severe deoxygenation”.
The oxygen levels were measured by underwater robots called Seagliders, which weigh 55kg and cost about £200,000 (Dh998,695) each. First developed about two decades ago and initially employed for naval use, these vehicles can be used in areas that may be dangerous because of political tensions or piracy. Because they use little energy, they can be sent out for months at a time, transmitting data back to the researchers via satellite at the end of each dive.
Manipulating an oil bladder within the Seaglider changes how heavy the vehicle is relative to the water around it, which determines whether is sinks or floats, while moving a large internal battery alters the centre of gravity and can be used to make the Seaglider tilt in any direction. It then glides through the water thanks to wings attached to the sides.
Dr Queste himself made at least eight trips to the area and travelled out to sea in a small dive boat provided by Sultan Qaboos University in Muscat, Oman, which played a key part in the research.
“We would sail out from Muscat and go about five nautical miles offshore,” he said.
The vehicles were deployed in about 200 metres of water at the edge of a shelf before the ocean floor falls away steeply and the water becomes much deeper, an area where, as Dr Queste put it, “the interesting stuff happens”.
The Seagliders were originally deployed in the Gulf of Oman to study bioluminescent algae, and it was only when oxygen levels were found to be much lower than expected that the research developed a new focus.
The study was recently published in the journal Geophysical Research Letters. The other authors are Dr Clément Vic, a postdoctoral research fellow in the National Oceanography Centre Southampton at the University of Southampton, United Kingdom, Professor Karen Heywood of the School of Environmental Sciences at the University of East Anglia, and Dr Sergey Piontkovski of the College of Agricultural and Marine Sciences at Sultan Qaboos University.
Dr Queste is now teaming up with a senior scientist at New York University Abu Dhabi, Dr Zouhair Lachkar, to carry out modelling that will offer a better view of what will happen to the Arabian Sea OMZ in future. As climate change and other factors continue to impact the natural systems across the planet, the researchers hope to be able to forecast how the local oceans will be affected.
Updated: May 4, 2018 01:35 PM