Mighty Lake Superior Mystifies Scientists
By JOHN FLESHER,AP
Posted: 2007-07-29 18:13:34
Filed Under: Nation News, Science News
MARQUETTE, Mich. (July 29) - As the research boat bobs up and down on
gray, choppy Lake Superior, Michigan Tech University chemist Noel
Urban and two students drop a metal cylinder over the side to retrieve
a water sample from the bottom.

They are measuring carbon dioxide content -- an unspectacular
statistic by itself, yet an important piece of a highly complex
puzzle.

"It helps us develop a model that can say what's going to happen as
the lake warms up," Urban says.

Plenty of people are wondering the same thing.

Something seems amiss with mighty Superior, the deepest and coldest of
the Great Lakes, which together hold nearly 20 percent of the world's
fresh surface water.

Superior's surface area is roughly the same as South Carolina's, the
biggest of any freshwater lake on Earth. It's deep enough to hold all
the other Great Lakes plus three additional Lake Eries. Yet over the
past year, its level has ebbed to the lowest point in eight decades
and will set a record this fall if, as expected, it dips three more
inches.

Its average temperature has surged 4.5 degrees Fahrenheit since 1979,
significantly above the 2.7-degree rise in the region's air
temperature during the same period. That's no small deal for a
freshwater sea that was created from glacial melt as the Ice Age ended
and remains chilly in all seasons.

A weather buoy on the western side recently recorded an "amazing" 75
degrees, "as warm a surface temperature as we've ever seen in this
lake," says Jay Austin, assistant professor at the University of
Minnesota at Duluth's Large Lakes Observatory.

Water levels also have receded on the other Great Lakes since the late
1990s. But the suddenness and severity of Superior's changes worry
many in the region; it has plunged more than a foot in the past year.
Shorelines are dozens of yards wider than usual, giving sunbathers
wider beaches but also exposing mucky bottomlands and rotting
vegetation.

"C'mon, girls, get out of the mud," Dan Arsenault, 32, calls to his
two young daughters at a park near the mouth of the St. Marys River on
the southeastern end of Lake Superior. Bree, 5, and 3-year-old Andie
are stomping in puddles where water was waist-deep a couple of years
ago. The floatation rope that previously designated the swimming area
now rests on moist ground.

"This is the lowest I've ever seen it," says Arsenault, a lifelong
resident of Sault Ste. Marie in Michigan's Upper Peninsula.

Superior still has lots of water. Its average depth is 483 feet and it
reaches 1,332 feet at the deepest point. Erie, the shallowest Great
Lake, is 210 feet at its deepest and averages only 62 feet. Lake
Michigan averages 279 feet and is 925 feet at its deepest.

Yet along Superior's shores, boats can't reach many mooring sites and
marina operators are begging the U.S. Army Corps of Engineers to
dredge shallow harbors. Ferry service between Grand Portage, Minn.,
and Isle Royale National Park was scaled back because one of the
company's boats couldn't dock.

Sally Zabelka has turned away boaters from Chippewa Landing marina in
the eastern Upper Peninsula, where not long ago 27-foot vessels easily
made their way up the channel from the lake's Brimley Bay. "In
essence, our dock is useless this year," she says.

Another worry: As the bay heats up, the perch, walleye and smallmouth
bass that have lured anglers to her campground and tackle shop are
migrating to cooler waters in the open lake.

Low water has cost the shipping industry millions of dollars. Vessels
are carrying lighter loads of iron ore and coal to avoid running
aground in shallow channels.

Superior's retreat creates a double whammy in Grand Marais, where the
only deepwater harbor of refuge along a 90-mile, shipwreck-strewn
section of the lake already was filling with sand because of a
decaying breakwall.

Burt Township, the local government, is extending the harbor's boat
launching ramp an additional 40 feet, Supervisor Jack Hubbard says.
Sand and shallow water are choking off aquatic vegetation that once
provided habitat for hefty pike and trout.

Puffing on a pipe in a Grand Marais pub, retiree Ted Sietsema voices
the suspicion held by many in the villages along Superior's southern
shoreline: Someone is taking the water. The government is diverting it
to places with more people and political influence - along Lakes Huron
and Michigan and even the Sun Belt, via the Mississippi River.

"Don't give me that global warming stuff," Sietsema says. "That water
is going west. That big aquifer out there is empty but they can still
water the desert. It's got to be coming from somewhere."

A familiar theory - but all wet, says Scott Thieme, hydraulics and
hydrology chief with the Corps of Engineers district office in
Detroit. Water does exit Lake Superior through locks, power plants and
gates on the St. Marys River, but in amounts strictly regulated under
a 1909 pact with Canada.

The actual forces at work, while mysterious, are not the stuff of spy
novels, Thieme says.

Precipitation has tapered off across the upper Great Lakes since the
1970s and is nearly 6 inches below normal in the Superior watershed
the past year. Water evaporation rates are up sharply because mild
winters have shrunk the winter ice cap - just as climate change
computer models predict for the next half-century.

Yet those models also envision more precipitation as global warming
sets in, says Brent Lofgren, a physical scientist with the Great Lakes
Environmental Research Laboratory in Ann Arbor. Instead there's
drought, suggesting other causes.

Cynthia Sellinger, the lab's deputy director, suspects residual
effects of El Nino, the warming of equatorial Pacific waters that
produced warmer winters in the late 1990s, just as the lakes began
receding.

Both long-term climate change and short-term meteorological factors
may be driving water levels down, says Urban, the Michigan Tech
researcher.

But he and Austin are more concerned about effects than causes.
There's a big knowledge gap about how food webs and other aquatic
systems will respond to warmer temperatures, they say.

"It's just not clear what the ultimate result will be as we turn the
knob up," says Austin, the Minnesota-Duluth professor. "It could be
great for fisheries or fisheries could crash."

That's a question Urban and his colleagues want to help answer with
their carbon dioxide measurements on Lake Superior. Plugging those and
other statistics into comprehensive ecosystem models will give
scientists a basis for making predictions.

"We're always reacting to what's already happened instead of looking
forward," Urban says. "As long as we have a poor understanding of the
basic functions of the lake, we won't be able to say whether this
warming is of major concern or not."

Editor's note - John Flesher is the AP correspondent in Traverse City
and has covered environmental issues since 1992.