A structure more than double the height of the Aerial Lift Bridge was pulled out of Lake Superior earlier this week.
A crew of researchers and students from the University of Minnesota Duluth’s Large Lakes Observatory, along with a marine crew, voyaged to a mooring located 30 miles south of Grand Marais on Monday. Throughout its two-month presence in the lake, it collected an "enormous amount" of data to help researchers study convection cycle.
The mooring project was “bigger and more complex than anything we’ve ever done,” said Jay Austin, the project’s principal investigator and a department head and professor of physics and astronomy at UMD. The complexity is twofold, as he referenced the towering size of the mooring and the large quantity of data it collected.
The mooring was nearly 1,000 feet wide and 500 feet tall. And it gathered the “most comprehensive set of data” on lake convection cycles that’s even been collected, according to UMD's website.
In early May, the nearly 46-story high structure was installed 100 feet underwater in an area away from shipping lanes.
One-thousand-pound cement blocks anchored steel cables that were suspended vertically in the lake, all of which were connected by a cable running horizontally. This large structure was the observatory’s first of its kind.
Grace Weber, a physics graduate student at UMD, was part of the installation and retrieval teams. Her role on the first trip was to attach sensors along the cables before they were lowered into the water.
For the last two months, the numerous sensors measured and recorded temperatures at various depths in the lake.
They will use the recorded data — which wasn't available to the researchers until they retrieved the structure — to create a "really coherent picture” of how the lake behaves during convection, Austin said.
Austin compares convection cycles to miso soup. In the hot Japanese soup, bubbles move through the broth as it cools. This is comparable — but on a much larger scale — to what happens in lakes during the convection cycle.
After winter in Lake Superior, warmer water is located at the bottom of the lake. This warmer water is less dense, so it rises to the top of the lake. This is also called lake turnover.
Convection dominates how the lake behaves for several months out of the year, Austin said. But it’s a process “that we know very little about.”
Weber will write her thesis about the collected data, but she said she doesn’t know what the thesis will look like until they retrieve the data. "It's going to be an insane amount of data. I'm honestly kind of terrified, but also very excited," Weber said.
“I have friends in different departments and … they don't have a lot of things to work with, because they're just modeling something or they're doing something fairly straightforward,” Weber said. “But this is a pretty large conglomerate of things that we're trying to put together in order to create a unified picture of this kind of unique convection.”
Because they're the first to tackle a study of this size about vertical heat movement in a lake, Austin said they have to create new ways to analyze the data.
The National Science Foundation funded the project, and the University also partnered with the University of North Carolina, Scripps Institution of Oceanography and University of California-Davis on it.
“I think one of the things that's important about what we're doing is, if we can figure out a way to … explain or better yet, categorize what's happening, then as people continue to look at it over the course of many years … we can start to notice how the heating of the lake is changing,” Weber said. “Which I think is obviously important for climate change.”