Piracy and political tensions in the Arabian Sea and its surrounding waters have long made it difficult for scientists to study the Gulf of Oman, a narrow stretch of water bordering Iran, Oman, Pakistan and the United Arab Emirates that connects the sea to the Persian Gulf.
But now that robots have gone where researchers have hesitated, they’ve helped discover that a major “dead zone” of oxygen-depleted waters in the area is bigger and growing more quickly than previously thought.
Militaries have developed the use of various crewless vehicles to surveil contested or dangerous waters, but, increasingly, remotely controlled robots called gliders and other autonomous underwater vehicles are also being deployed by scientists to study the ocean’s health in treacherous geopolitical conditions.
As reported in a recent study in the journal Geophysical Research Letters, researchers dispatched two Seagliders in 2015 and 2016 over eight months in the Gulf of Oman, which the United States defines as a “high-risk area” at significant risk for piracy. In their study, the scientists write that since the 1990s, threats of piracy – as well as political and logistical difficulties – have hampered observational programs in the Arabian Sea region. But the gliders were able to communicate by satellite to scientists stationed out of harm’s way.
Seagliders are no larger than a human diver, but they traverse large areas of ocean using little energy. As a result, they can travel for months, covering thousands of kilometers and diving from the surface to depths of as much as 1,000m (3,280ft). The gliders can be directed from shore through a satellite connection when they surface, as well as send data back. For the Gulf of Oman study, the robots were outfitted with sensors to collect a variety of data, including oxygen concentrations, and repeatedly surveyed a 76km (47-mile) stretch of water, making more than 1,000 dives each.
Bastien Queste, a marine biogeochemist at the University of East Anglia in the United Kingdom and the study’s lead author, said that without the gliders the researchers would have needed to go out with a ship and drop a device over the side to gather samples and data every 10–15m (30–50ft).
That would have been risky, he said, because the scientists would have had to spend more time in contentious waters. (These fears have been warranted in the past. In 2001, a research ship was pursued by pirates off the Somali coast.) By just dropping sensors over the side of boat periodically, the researchers would also have missed out on making close measurements of how the gulf’s eddies affected the circulation of low-oxygen waters, which the gliders were able to pick up as they drifted in the currents.
For the most part, the goal of the gliders and similar devices used in research is to get where people can’t go – like under ice shelves, as a current University of Washington project is doing – or to save money and time in gathering measurements. While expensive, these machines can reduce or eliminate the cost of hiring a ship and paying and feeding a crew for several days or weeks. But sometimes it’s not the physical act of getting somewhere that makes a place hard to study.
“These have been around for 20 years, so, of course, people are going to start using them in more and more dangerous places,” said Fritz Stahr, who manages the Seaglider Fabrication Center at the University of Washington’s School of Oceanography and was not involved in the new Gulf of Oman study. “There’s a tremendous amount of places we can’t get to. These vehicles present a great solution to that problem.” That includes, he said, places where there are pirates.
Queste and his colleagues have also previously used gliders in the Bay of Bengal and in the East China Sea, where territorial disputes over small islands have raised political tensions and traveling close to shore risks provoking authorities. Stahr also recalled a time when researchers operated a glider around an island of “contested nationality” in the East China Sea. The device ventured too close and they decided to scuttle the glider rather than risk it being discovered, he said. He didn’t think that was necessary, though.
“Like a lot of robots, they don’t have much of a footprint. They have a very small footprint when at the surface – just an antenna sticking out,” Stahr said. Gliders are even less visible if they’re painted all gray, like some he said he helped build for the United States Navy.
There are rules about using gliders, Stahr said – if you want to operate within a country’s territorial water or exclusive economic zone you should request permission or notify authorities of the robot’s presence, for instance – but most of the time there’s little chance the device is noticed.
If it is seen, it could be stolen. Stahr recalled a situation in which a Taiwanese fishing crew picking a glider off the surface and held it as it was approached by the research vessel. The researchers ultimately got it back in exchange for about 10lb of steak and a couple gallons of ice cream, he said.
There’s also the risk of a device like a glider itself raising suspicions. “Especially in more militarized areas, you run the risk of someone thinking that a drone poses a threat and [them] taking some action accordingly,” said Mark Schrope, director of Schmidt Marine Technology Partners, a program of the Schmidt Family Foundation that funds early-stage ocean technology startups. “But I suppose that’s the cost of doing business.”
In the Gulf of Oman, the technology allowed researchers to conclude that an oxygen-minimum zone, or dead zone, is growing. It is an extension of the dead zone in the Arabian Sea, which is the world’s largest and thickest area of oxygen-deficient waters in the world. Unlike the Gulf of Mexico dead zone off the coast of the United States – an expanse of low-oxygen waters created each summer after fertilizer and sewage runoff is carried to sea – the Arabian Sea dead zone is naturally occurring and hundreds of millions of years old. But data on the phenomenon has been deficient.
The study found that, after being relatively stable for a long time, oxygen concentrations in the Gulf of Oman have dropped dramatically since the 1960s. Even compared to the data from the 1990s, Queste’s study found oxygen concentrations were surprisingly low.
Using computer models, the study found that those low-oxygen waters could spread throughout the northwestern Arabian Sea and, ultimately, the Indian Ocean. “The net effect is that the oxygen-minimum zone is growing horizontally and vertically,” he said.
Growing vertically means the layer of water with enough oxygen for most fish is shrinking. That decrease in available habitat could have hurt marine life, including commercially valuable species. As one example, Queste noted that fish like tuna might be restricted to surface waters, making them easier for fishing vessels to catch and making them appear, inaccurately, more abundant than they are.
Having the new data could help scientists forecast how marine life will be affected by the dead zone and forecast how it could spread. In general, sea-going robots will continue to be useful to study this and other difficult regions. As for explicitly using gliders and robots to reduce the risks of stirring up political tensions or encountering piracy, “it sounds like a really promising application, and it’s one I hadn’t really thought of,” Schrope said. He added that it’s not a benefit to the technology the foundation has actively promoted, but that they “would certainly be in favor of it.”