Using Underwater Drones to Monitor the Oxygen Levels in the Arabian Sea

For many years, researchers have known that the waters in the Arabian Sea were in trouble. In the early 1960s, and then again in the 90s, scientists were able to conduct some minimal research to test the oxygen minimum zone (OMZ) around the Arabian Sea. The results showed that the oxygen levels were dangerously low. Low oxygen levels lead to what is known as a dead zone because nothing can survive without oxygenation. Dr. Bastien Queste of the University of East Anglia was particularly concerned about the current state of the Arabian Sea’s OMZ. “The Arabian Sea oxygen minimum zone (OMZ) has been here for as long as we know,” Dr. Queste said. “Because of piracy and geopolitical tension, we haven’t been back to do large mapping studies, and so have kept this ‘mental picture’ of oxygen distribution since then, and used it in all of our computer modeling and forecast studies.” The data being used to monitor these waters were so out of date that researchers like Dr. Queste had no clear idea as to how damaged the area had become.

As climate and environmental changes have negatively effected other areas of the world’s water supplies, Dr. Queste was determined to remap the Arabian Sea OMZ. But since it is still not safe to send research ships and divers into the area, he had to find an alternate way of gathering data. Dr. Queste and his team turned to one of the world’s leading marine systems providers, Kongsberg. The Norwegian marine technology company has been leaders in marine research and enterprises for more than 200 years. Recently they have been changing the way scientists conduct marine research with the development of an autonomous under water drone, the Seaglider.

As explained on Kongsberg’s website, “Seaglider Autonomous Underwater Vehicles have revolutionized the collection of ocean data. Their change in buoyancy make them move through the water column in a saw-tooth pattern, surfacing often to determine its position while continuously collecting data. This results in very low power consumption and long endurance of up to 10 months depending on configuration and payloads. Navigation is accomplished using a combination of GPS fixes while on the surface and internal sensors that monitor the vehicle heading, depth and attitude during dives. External sensors are constantly scanning the ocean to determine environmental properties.” This drone was clearly a device that Dr. Queste could use to safely gather the data he needed.

Dr. Queste and his team deployed two Seagliders into the Gulf of Oman for 8 months to gather data. The Gulf of Oman is the body of water connecting the Arabian Sea with the Strait of Hormuz, running into the Persian Gulf. It is bordered by Iran, Pakistan, Oman and the United Arab Emirates. While the gulf would be unsafe for Dr. Queste to explore, it is still a vital source of food and income for the people living around it. The data collected by Dr. Queste brought back results that can prove to be devastating for the animals and people who depend on the Gulf of Oman and it’s surrounding waters. The OMZ previously recorded had changed so drastically that the Gulf of Oman is now considered the largest oceanic dead zone on the planet.

The Seagliders remotely patrolled the gulf, communicating back to Dr. Queste via satellite. They very slowly traveled through the waters up to 1,000m deep without Dr. Queste needing to put himself at risk by entering the gulf even once over the 8 month mission. Dr. Queste said it is due to the Seaglider’s ingenious system that this is possible. “They have an oil-filled bladder that they use in the same way as fish use their bladders,” he explained. “They fill it with oil, so their volume goes up while mass stays the same, or bring the oil back into the hull so the volume goes down, and mass stays the same, to change the density of the vehicle. The vehicle’s density relative to the water around it defines whether it sinks or floats. This way it only has to use its motor twice: once at the surface to start sinking, and once at the bottom to start floating again.”

While the drones were in the water Dr. Queste was already able to start analyzing the data being sent by the satellite. “The OMZ is a natural phenomenon, and the Arabian Sea has always been the most intense,” explains Dr. Queste. “However, we thought it was anoxic (= 0 oxygen) in the core, but that oxygen went up to concentrations above suboxia (> 6 in the margins. The oxygen has dropped dramatically in the Gulf of Oman, which now means there’s a whole different type of biochemical cycling going on. Bacteria now have to ‘breathe’ nitrate instead of oxygen (= denitrification). This is what produces the greenhouse gas nitrous oxide.” Dr. Queste is not entirely sure what has caused this shift, though he does suspect it is due to global climate change.

Clearly there is a major problem growing in the Arabian Sea. Armed with tools like drones, Dr. Queste is set to continue his research to find out what factors ultimately have led to the Gulf of Oman becoming a massive dead zone. There are still many questions to be answered, but what Dr. Queste is sure of is the dire consequences this dead zone will have on people. “The impact for us is how rapidly it is changing, putting stress on valuable ecosystem resources that we depend on heavily,” he went on to say. “For example, the tuna fishery near Oman is huge and very affected by the growing OMZ which compresses fish into a thinner layer at the surface. If we’re not careful, we’ll suspect there are more tuna (more per unit volume of water), but in reality, there are the same number, simply stressed and squeezed into a smaller space.” As Dr. Queste launches into the next stages of his study with the Seagliders he is also encouraging any young minds with a concern for the environment to get an education and join him in his research.

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