University of Minnesota
Researchers prepare to place one of the new autonomous moored profilers into Lake Superior aboard the Blue Heron research vessel. The profilers will be the first used on this scale in a large lake.
Photo: Brett Groehler, UMD
Great news for a Great Lake
High-tech profilers will help keep tabs on Lake Superior year-round
By Rick Moore
Early in August, Lake Superior gleamed a deep, indigo blue as viewed from the paths along its shore next to downtown Duluth. But in this case, what you can see with the naked eye doesn’t tell the full story.
Six weeks earlier a massive rainfall—nearly 10 inches in less than 24 hours—triggered an epic flood that ravaged parts of the city and eventually caused the lake to rise by an astounding 3-4 inches. And while much of the brown clay sediment that turned the Duluth-Superior harbor chocolate-milk brown had settled to lower depths, scientists have no way to fully calculate the flood’s effects on Lake Superior.
Keeping better tabs on a lake that is undoubtedly one of Minnesota’s (as well as the nation’s) most precious resources is of increasing concern. And the University is now better equipped to do just that, thanks to the arrival of two “autonomous moored profilers” (profilers, for short) that will be used by the Large Lakes Observatory (LLO) at the University of Minnesota, Duluth.
Data collection for all seasons
Each profiler is shaped like a large water heater, with a clear encasing housing an array of instruments and a winch built into its base. The profilers, which will be anchored at a depth of up to 100 meters in two locations in the lake, can automatically be raised and lowered throughout the entire water column at regular intervals throughout the day, taking readings along the way.
They will enable the LLO researchers to collect a wide range of data, including temperature, depth, currents, conductivity, turbidity, dissolved oxygen, nitrate concentration, light intensity, and a suite of fluorescence measurements.
The sensors can surface and transmit data back to shore in near real time, or store the data when that can’t happen, such as when the lake is covered with ice.
According to Jay Austin, a UMD physics professor and lead PI on the project, these will be the first profilers used on this scale in a large lake. They were originally designed for oceanographic work, he says, “and we’re adapting oceanographic technology for the study of large lakes.”
While the LLO has long been taking readings of Lake Superior, largely via an array of moored instruments and an autonomous glider, the measurements have generally been at discreet depths, usually 10 meters or below, or when it’s suitable for boats to be out on the lake.
“This is going to allow us to make measurements on the upper part of the water column (where a lot of biological activity occurs),” says Erik Brown, a UMD professor in geological sciences and co-PI on the project. “As the profilers go up and down, they’re continuously measuring water properties.
“And the really exciting thing is, it’s letting us look at what’s happening in the upper part of the water during winter, which is kind of a black box. … There aren’t measurements on what’s happening out there during almost half of the year.”
Tracking events large and small
Having tools like the new profilers will be invaluable as researchers try to get their arms around the changes and trends occurring in Lake Superior and, for that matter, in lakes worldwide. Until recently, they weren’t aware that what happens during the winter directly affects how warm Superior will get in the summer.
And no one was prepared to study the effects of a flood of the century. But “the instrument package on these profilers is extremely well-suited for looking at that type of phenomenon,” notes Brown.
“The lake is changing,” says Steve Colman, director of the LLO. “People think it’s so big … that it’s static. It’s clearly changing in response to climate change issues—in our opinion.
“But that’s not the only thing that’s going on. There are human pressures. There’s pollution. There are invasive species. All of those things are causing the lake to change— sometimes in perceptible ways, sometimes in ways we can’t really see unless we go over a non-linear cliff and cross a threshold.
Grad options in water science
In addition to conducting research on Lake Superior, UMD is also bringing the research into the classroom with the Water Resources Science graduate (M.S. and Ph.D.) program. Students develop the breadth of scientific knowledge needed to understand the complicated aquatic ecosystems and watersheds on which they operate.
“We certainly won’t understand them if we’re not out watching and making measurements. That’s what we try to do.”
The new profilers will go a long way toward accomplishing that.
“In Lake Superior, the season where it’s nice to go out there [on a boat] is relatively short, but there’s science year-round out there,” says Austin. “So we’re very interested in being able to have something collecting a wide variety of data over the course of the year.
“Biology doesn’t stop because the weather’s bad.”
The two profilers are funded by a $485,000 grant from the National Science Foundation’s Major Research Infrastructure program.