The ocean absorbs almost a quarter of the carbon dioxide generated by human activity, and in doing so chemical reactions take place that make its waters more acidic. Measuring this effect is possible to an extent with sensors fitted to stationary buoys and vessels, but a newly fitted out deep-diving underwater drone promises to fill in the blanks in a big way, offering an autonomous method of tracking CO2 uptake in remote corners of the ocean, and far beneath its surface.
Rising acidity in the ocean poses a serious threat to marine life, impacting on the viability of coral reefs and shellfish by eating up the calcium carbonates they use as building blocks for their unique structures. We've also seen studies suggest more acidic oceans could reframe predator-prey relationships, interfere with the survival instincts of fish, and dissolve mossy sea creatures or even the ocean floor itself.
To get a better handle on the problem, in 2018 oceanographer at the University of Alaska Fairbanks Claudine Hauri set out to address the gaping holes in CO2 sampling of the ocean. This kind of data is usually collected by research vessels traveling dedicated routes or by time-series measurements from sensors on fixed moorings. Hauri's idea was to deploy an autonomous vehicle that could travel far and wide and plunge the ocean's depths to give more accurate readings of the transformations taking place.
This led Hauri and her team to an existing underwater drone called the Seaglider, which was developed at the University of Washington and commercialized in 2013. The drone can cover thousands of kilometers on each journey and operate at sea for months at a time, with the ability to dive to depths of up to 1,000 m (3,280 ft).
Equipping the Seaglider with the right capabilities involved taking the most precise underwater carbon dioxide sensor on the market and reworking its design. The original sensor was too large and power-hungry to be carried by the Seaglider, so electronics engineer and partner on the project Ehsan Abdi had to modify it to be lighter and more compact.
“The most exciting thing is seeing such a big and power-hungry sensor go on such a humble and small glider that was not meant to do stuff like this,” he said. “That’s why it’s challenging, and that’s why we’ve had so many problems. But that’s the fun part of it as well.”
With the Seaglider suitably equipped, the team carried out testing in tanks to balance the vehicle correctly and make sure its sensors were producing accurate measurements. The team then proceeded to its first open water testing, deploying the drone in Alaska's Resurrection Bay to gather real-world data. This makes the team the first in the US to measure ocean CO2 with an autonomous underwater vehicle, and it plans to share the technical details of its sensor integration so other teams can join the cause.
“I’m excited by the possibility of having a whole fleet of these Seagliders continuously measuring CO2," said team member Jöran Kemme from 4H JENA Engineering, who worked on the sensor integration. "It’s important to have people from all around the world working on this, especially because it is a worldwide issue."
Source: University of Alaska Fairbanks
