Warm Waters

     The lakes of the Boundary Waters and Quetico Canoe Country are warming up.  They are perfect for a refreshing morning, afternoon or evening swim.  It’s one of our favorite things to do while we’re out camping in the BWCA.  I love to pick an island off in the distance and see if I can make it there and back; so far I have been successful. I don’t normally swim in Lake Superior because it is usually pretty cold but this year I may just find myself taking a few dips in the big lake in Grand Marais.

Published July 15 2010

Warmer Superior temps expected

Researchers at the Large Lakes Observatory of the University of Minnesota Duluth predict that the surface of the open waters of Lake Superior will be exceptionally warm by August. They suspect that water temperatures may exceed the high recorded during the strong El Niño summer of 1998, 68 degrees.

Researchers at the Large Lakes Observatory of the University of Minnesota Duluth predict that the surface of the open waters of Lake Superior will be exceptionally warm by August. They suspect that water temperatures may exceed the high recorded during the strong El Niño summer of 1998, 68 degrees.

The average water temperature of Lake Superior’s surface waters in August is about 59. It’s already about 59 degrees at a buoy northwest of the Apostle Islands.

Jay Austin, associate professor of physics, and his collaborator Steve Colman, professor of geology, report that this past winter’s low ice coverage led to an early spring turnover and an early onset of summer stratification in the world’s largest freshwater lake by surface area.

Early stratification will allow the lake’s surface waters to warm for a longer time. This year, the lake began forming layers in early- to mid-June rather than the normal mid-July. From now until autumn, the surface waters will continue to warm and blanket the colder waters. When Austin noticed that the lake was headed for early stratification, he said that this “typically means that it’s going to be a very warm year in Lake Superior.”

Lake turnover happens as the winds “turn over” the lake, mixing the water column until the water reaches about 39 degrees. At that temperature, the water column begins to “stratify,” where warmer water forms a layer over the colder waters below.

In 1998, a warm year, the lake peaked at 68 degrees, “and we’re well on our way to that, or higher,” Austin said. That compares to a high temperature of just 54 degrees in August 1996, a cool year.

Austin and Colman grab-bed headlines in 2007 for showing that summer water temperatures were warming twice as fast as air temperatures over the last 30 years, based on data from buoys in Lake Superior. The reason for the warming was partly due to increasing air temperatures, but also strikingly related to winter ice cover. The less winter ice, the earlier the summer stratification begins, and the longer the summer heating season for the surface waters.

“After watching last winter’s ice cover, I suspected that Lake Superior was in for warm summer surface water temperatures as much as five months ago,” Austin said. “The early stratification date this year adds weight to my suspicions.”

Scientists are just starting to study what the rapidly rising water temperatures might mean for the big lake.

It could mean a more fertile lake with more organisms that thrive in warmer conditions. And it could cause “cascading biological effects to fish and other species that we can surmise but haven’t confirmed as of yet,” Colman said.

Lake Superior’s warming waters could alter the productivity of microbes and algae, affect commercial and sport fishing, and create a longer recreational summer season. Swimmers might rejoice but lake trout may have to move deeper or further offshore.

The warmer water not only means more swimmable water earlier this summer but also warmer breezes for people on shore. Now, even when winds are off the big lake, they’re more refreshingly cool than chillingly cold.

“If you’re dealing with water temperatures that are as warm, or nearly as warm, as the air, there is no ‘cooler by the lake,’ ” said Alex Lamers, meteorologist with the National Weather Service in Duluth.

“Cooler is a relative thing. If it’s mid-80s inland and mid-70s by the lake, that’s considered pretty comfortable. We’re not seeing those huge temperature differences now that we do” when the water temperatures are lower, he said.

Visit Minnesota Sea Grant’s climate portal at: www.seagrant. umn.edu/climate/. For access to the University of Minnesota Duluth’s buoy data, see: www. d.umn.edu/~jaustin/buoy_ 2010/