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Satellite_Superior_and_Michigan_Jan272012

Photo courtesy of Space Science and Engineering Center, University of Wisconsin-Madison

Satellite photo shows minimal ice coverage on Lake Superior and Lake Michigan this winter. Cloud cover obscures the right side of the image. 


Great Lakes on thin ice this winter

by Rory Keane
Feb 02, 2012


navy_pier_no_ice

Rory Keane/MEDILL

The lakefront as seen from Chicago's Navy Pier.  Unseasonably warm temperatures have even allowed open fishing on the waters by Navy Pier this winter.

Satellite_Superior_and_Michigan_Mar2009

Photo courtesy of National Weather Service

This satellite photo, taken in March of 2009, offers a glimpse of widespread ice coverage on the Great Lakes. Most of Lake Superior (top) is encased in ice.

The frozen moonscape of an ice-covered beach can be awe-inspiring, eerily beautiful, and all too familiar in winter across the Great Lakes.

But this winter is largely bereft of these frosty vistas and that could impact the ability of some fish to spawn.

Even though many lakeside residents may enjoy the more temperate beachfront this year, ice plays a pivotal role in maintaining some unsung real estate: coastal wetlands and water depth.

The wetlands act as an incubator for much of the wildlife in the Great Lakes basin.

Wetlands - the marshy shorelines that harbor countless plants and animals - thrive on the constant fluctuation of the seasons and Great Lakes water levels. Not having substantial ice coverage allows for greater evaporation. And evaporation leaves water levels across the Great Lakes lower over a prolonged span of time.

“Having low water levels next year doesn't make me nervous. Having low levels over the last 10 years makes me worry,” said Donald Uzarski, director of Central Michigan University’s Institute for Great Lakes Research.

“We’ll see what happens with respect to the water levels,” he said. “When the water level's lower, the coastal wetlands stretch out towards the water's edge," out into exposed shoreline areas that are usually under water.

Many of the large, predatory fish—even those that live in deep water—rely on the wetlands as a feeding source for invertebrates and small fish that supply the food chain in the lakes. These larger fish will use the wetlands as a nursery area as well.

Without ice to cover wetlands, wave activity and wind can push out fragile fish eggs, driving them into deeper water and destroying them before they spawn.

Extreme temperatures from summer to winter are actually considered good for wetlands. An up and down trend can feed the growth of wetlands, which are “very dynamic and very responsive to water levels,” according to Kurt Kowalski of the United States Geological Survey.

But what climatologists studying lake ice have noticed is a steadier pattern of temperatures within the last ten years. “The Frequency of mild winters has been on the increase. We’re certainly in a trend for milder winters now,” said Ray Assel, a retired climatologist, recently of the Great Lakes Environmental Research Laboratory.

Beyond the impact of mild winter on ice, the extreme storms in the region can lead to a decline in ice coverage as well. “If you have storm passages over the lake, you have upwelling of deeper waters which are warmer, and you tend to melt any ice towards the shores,” Assel said.

The combination of milder winters and extreme storms certainly detract from ice coverage, but their overall effect on coastal wetlands has yet to be measured in-depth.

“There's not a big body of knowledge on the direct impacts,” Kowalski said.

While observations continue to come in during this unseasonable warmth, a helpful analogy for understanding the wetlands may come from your home.

“Imagine in your garden things are blooming earlier than they should, and something’s not quite right,” said Paul Seelbach, a professor of fisheries science and biology with the United States Geological Survey. This is a very apt comparison, especially for anyone who’s taken pains to cover tomato plants to safeguard them from fatal frostbite.

“It’s all about timing,” he said.