Gliders provide in-depth scientific data on Lake Superior
Gliders are becoming the standard tool for oceanographic research.
ON LAKE SUPERIOR - Jay Austin and Tom Hollenhorst stood in the boat, scanning the lake’s surface around them in the hope that they would see an underwater glider’s yellow tail sticking out of the water, buoyed by its “bladder” inflating to bring it to Lake Superior’s surface. The autonomous underwater glider named Nokomis, looking like a small, unmanned submarine with wings and a tail, had been traveling on a 700-mile, 37-day journey across Lake Superior to collect data in the depths of the lake that researchers can’t typically access.
Gliders are becoming the standard tool for oceanographic research, said Austin, a University of Minnesota Duluth physics professor who works at UMD’s Large Lakes Observatory. “There are hundreds of these around the world for oceans and there are three of them that have been built for freshwater. Two of them are here in Duluth, so Duluth has really cornered the market on glider activity on the Great Lakes,” Austin said.
This is UMD’s seventh year operating one of those two gliders, named Gichigami and purchased by UMD with National Science Foundation funding. The U.S. Environmental Protection Agency has owned Duluth’s other glider, the Nokomis, for three years.
Dropped into the water Sept. 13 near Michigan’s Whitefish Point, the Nokomis was slated to be reunited near Duluth on Friday with Austin and Hollenhorst, an ecologist with the EPA.
On Friday afternoon, UMD’s research boat Kingfisher slowed down on Lake Superior as it approached the geographic coordinate off the shore north of McQuade Small Craft Harbor, intended to be the reunion location. Austin explained that the boat needed to be parked at the location so it didn’t inadvertently run over the Nokomis as the glider, about 4 feet long and weighing 125 pounds, rose to the water’s surface. The concern is always that a boater will unknowingly run over the glider and damage it while it’s surfacing. However, operating a glider in Lake Superior doesn’t present the same worries scientists have operating a glider in the ocean - damage from saltwater and sharks.
“We’re saltless and shark-free,” Austin said.
Although the Nokomis is bright yellow, it can be difficult to spot in the water unless it’s near the boat. But even after spending time looking around on the water’s surface for the Nokomis, it still couldn’t be seen. Austin texted Paul McKinney back at the Large Lakes Observatory, who reported back that the Nokomis wasn’t communicating with him at the lab. “It’s unnerving when you’re waiting for it to come up and it doesn’t,” Austin said, adding that the glider has redundancies to ensure it continues to function if something malfunctions.
But then McKinney reported that the Nokomis had communicated its location and overshot the meeting coordinate by a kilometer, likely because it hit a current and overcorrected.
As the boat headed toward the glider’s location, the dark dot of the Nokomis’ tail sticking out of the water became visible in the distance. Once the boat sidled up to the Nokomis, it took three people to slide the glider into the boat and strap it in. “It’s really satisfying to see this thing after that long,” Austin said.
Twenty-four hours a day, the Nokomis traveled slowly through the water at a pace that’s “like going for a walk with your grandparents,” Austin said. A glider propels itself forward by changing its buoyancy to create an up-and-down motion, which causes it to use little of its battery power, Hollenhorst explained. The lack of battery usage means the Gichigami can operate underwater for 25 days and the Nokomis can last for nearly 100 days.
McKinney sets GPS coordinates for the glider to visit based on interesting places he sees on satellite imagery of the lake. The trip the Nokomis completed on Friday included stops around Michigan’s Keweenaw Peninsula and along Minnesota’s North Shore between Lutsen and Grand Marais.
Once the glider dives underwater, staff can’t communicate with it, Austin said. It surfaces when it reaches the coordinate or about every six hours, sending text messages to lab staff with information such as its remaining battery power and geographic coordinate. It’s only when it surfaces that staff can tell it a different coordinate to visit or, in the case of Friday, tell it to remain at its current location in order for staff to pick it up.
UMD and the EPA have deployed the gliders seven times on Lake Superior so far this year, totaling more than 100 days spent collecting data in the water, and Austin said they still hope to deploy a glider one more time before ice forms on the lake. The public can follow the gliders’ movements online at d.umn.edu/buoys/gliders.php . Austin noted that he receives phone calls and emails from boaters who see the gliders while they’re out on Lake Superior, and staff ask that boaters leave a glider alone if they see it.
As the glider travels, it surveys the water around it to document its characteristics. A glider can profile the water to a depth of about 500 feet, giving scientists more in-depth information about the lake, Austin said. “What we’re trying to do with the glider is to provide a little bit of context in the sense of, when we see features at the surface of the lake, what do they look like below? If we see warm water, how much warm water is there?” he said.
There’s a narrow weather window in which researchers can be on the lake, leading to “fair weather bias” in the results, Austin said. “In other words, we only collect data during nice conditions, but the lake keeps ‘laking’ when the weather’s bad. In fact, a lot of interesting things happen when the weather’s bad. You’ve got lot of wind mixing and stirring and all these other things going on, and the glider allows us to have a persistent presence in the lake,” Austin said.
He said one item he’s researching is shifting sediment in the lake, which often happens in bad weather - and the glider can collect the data on sediment close to the lake’s bottom during bad weather.
Staff download the data once a glider is back at the lab. Hollenhorst said they’ll spend the winter analyzing the data collected by the gliders, and that will then go into scientific papers.
Hollenhorst said the glider research is a collaboration with the EPA’s Great Lakes National Program Office and is part of its Coordinated Science and Monitoring Initiative, in which staff research a different Great Lake each year. UMD’s glider research creates base data that supplements the EPA’s research on water quality and can be used to determine changes in the lake, especially due to climate change, Hollenhorst said.
“It helps us detect those subtle changes over time,” he said.