MINNEAPOLIS — Lake Superior is the largest freshwater lake in the world — a sea known for its pristine cold water. But in a warming world, that's changing.
Before dawn, a crew boards the Blue Heron, an old fishing boat converted into a floating lab for research.
The Department of Natural Resources checks on the lake's fish populations to manage and support one of the state's great resources and pastimes. On a chilly Madison Lake in central Minnesota, they're electro-shocking those fish to collect samples. Experts then look at their size, age and diets to get a baseline, then compare it to winter.
As students work on the water, professors like oceanographer Jay Austin are back at their home base — the Large Lakes Observatory at University of Minnesota Duluth.
Austin says Superior has warmed one degree per decade since the 80s, making it one of the fastest-warming lakes in the world.
"Temperature is sort of this master control knob on how ecosystems work," Austin said.
Austin's colleague, Ted Ozersky, says that's churning a number of concerns.
"If we look at historical trends over the last 100 years, we've lost about 15 days of ice cover," Ozersky said. "So loss of ice and loss of winter is stimulating these summertime algal blooms."
In July 2012, the first algae bloom ever recorded was spotted on Lake Superior. About 30 days after a 500-year storm washed zoo animals out of their enclosures, dumping sediment into the lake that could be seen from space.
"It's by far the cleanest and the clearest of all of the great lakes," Ozersky said. "And it's size. It feels like an ocean."
Anthropologist John Shepard from Hamline University was there this summer as six marathon swimmers set a record going from Two Harbors to Duluth. No wetsuit needed in this balmy 60-degree water — something unimaginable just a short time ago.
"People everywhere are witnessing climate change no matter where you live," Shepard said. "So in this region, some of the changes we're seeing in Superior is one of the ways this comes to life for people."
A warming Superior opens doors for different types of recreation — perhaps a longer commercial shipping season.
But in the face of these changes under the ice, above it and without it, there's no question — Superior's frigid legacy is changing.
"Why do people care so much about our large lakes?" WCCO's Erin Hassanzadeh asked.
"Fresh water is a tremendously important resource," Austin said. "The five lakes we have right here, are 20% of the world's fresh surface water."
"It's such an important part of our regional heritage," Shepard said.
"Ice gives us a sense of place, and that is changing over time," Austin said. "We don't want things to get worse, right? And so we have to understand how they work,"
In a recent study, ice expert Sapna Sharma with New York University said, "If we continue emitting greenhouse gases at this rate, Lake Superior will not freeze after the 2060s."
For stories about how winter is changing across the country, and to watch the documentary "On the Dot" please visit Arctic melting foreshadows America's climate future.
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