Warmer means windier on world's biggest lake

Science Daily: Rising water temperatures are kicking up more powerful winds on Lake Superior, with consequences for currents, biological cycles, pollution and more on the world's largest lake and its smaller brethren. Since 1985, surface water temperatures measured by lake buoys have climbed 1.2 degrees per decade, about 15 percent faster than the air above the lake and twice as fast as warming over nearby land.

"The lake's thermal budget is very sensitive to the amount of ice cover over the winter," says Ankur Desai, atmospheric and oceanic sciences professor at the University of Wisconsin-Madison. "There is less ice on Lake Superior during the winter, and consequently the water absorbs more heat." A wide temperature differential between water and air makes for a more stable atmosphere with calmer winds over the relatively cold water. However, as warming water closes the gap, as in Lake Superior's case, the atmosphere gets more turbulent.

"You get more powerful winds," Desai says. "We've seen a 5 percent increase per decade in average wind speed since 1985."

…In theory, that increase in wind and current strength would make for more mixing within the lake and, in turn, a boost in the growth of organisms that make up the earliest links in the food chain. But Lake Superior's chlorophyll levels -- a measure of the presence of phytoplankton -- have been falling. The effect went largely without explanation until the researchers' modeling showed that the period of temperature stratification (well-defined separation of cold, deep water and warm surface water) was growing alongside surface temperatures and wind and current speed…..

Photograph of Lake Superior from Brockway Mountain in the Keweenaw Peninsula of Michigan. Shot by Charles Dawley Flickr Profile, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 License