Great Lakes ice coverage declines as the climate warms

The last bits of winter snow and ice in the Great Lakes melted in late May, according to a NOAA-GLSEA (Great Lakes Surface Environmental Analysis) tracker that uses satellite data to produce real-time daily estimates of Great Lakes ice coverage.

Before it melted, scientists collected samples of ice, snow and frosty lake water in a coordinated scientific event called Winter Grab, a research effort to assess the winter conditions of the Great Lakes and Lake St. Clair. More than a dozen teams of scientists from the U.S. and Canada participated in the inaugural event, which took place during a single week in February. The shared results will provide the first systematic baseline of winter conditions on the Great Lakes, giving important clues about how climate is affecting lake ecosystems as a whole.

Using precise scientific instruments as well as ordinary tools like ice picks, slotted spoons and plastic jugs, decentralized teams across all five lakes drilled their way through the ice to collect water samples, measure underwater light levels and gather plankton and other microorganisms. The data will help them better understand ice properties, water chemistry and lake biology, as well as help them determine how the lakes are influenced by the changing climate.

Winter Grab was organized by University of Minnesota Duluth associate professor Ted Ozersky, who also organized the Great Lakes Winter Network (GLWiN), a research collaboration between multiple organizations. "Over the last few years, lake scientists increasingly recognized that we know very little about what lakes do in the winter," Ozersky says. "Part of the motivation for Winter Grab is to fill this big information gap. The other motivation is climate change."

Michigan native Emily Elconin photographed two teams that participated in the effort, joining them on Lake Erie and Lake Huron. Here's a look at the how scientists are advancing our understanding of the impacts of climate change on the Great Lakes:

Warming climate, less ice

While ice coverage on the Great Lakes has always been highly variable, longitudinal data from NOAA indicate a downturn in winter ice coverage over the last few decades. EPA data shows that the average number of days the lakes are frozen each year has declined across all five Great Lakes since the 1970s.

Estimates presented by the International Joint Commission, an organization created to ensure that the U.S. and Canada work effectively together on Great Lakes issues, indicates that ice coverage on the lakes has declined by 71% between the early 1970s and 2010. Not only is there less ice overall, but the ice that does form isn't as thick and doesn't remain on the lakes as long as it did in previous decades.

Climate change is a key factor driving the reductions in ice coverage. "How the ice forms on the Great Lakes and how long it is out there is very climate-dependent," says Bowling Green State University emeritus biology professor George Bullerjahn. "[Ice levels] are not dependent on temperature as much as climate patterns."

Increased attention to winter water sampling

Scientists have studied the relationship between the Great Lakes' ice cover and the region's climate for decades. Teams at NOAA-GLERL (Great Lakes Environmental Research Laboratory), for example, have monitored and analyzed ice coverage on the Great Lakes for more than 30 years, linking their data to climate patterns, water levels, water temperature and the composition of biotic communities such as zooplankton and fish. Typically, however, "most water sampling has been conducted between spring and fall," when the lakes aren't frozen and navigation and sampling are easier, says Bullerjahn.

Until recently, that seasonal gap in data didn't concern scientists. Thick layers of ice and snow on the surface of the lakes prevent light from passing through to the water below. The resulting darkness, along with cold winter water temperatures, significantly slows down aquatic activity, leading to a long-standing belief that lakes were mostly dormant during winter. Without sampling the lake directly, however, "winter conditions and processes were like a black box, with autumn going in on one side and spring coming out the other side. What actually was happening in the water during winter was a bit of a mystery," says Ozersky.

Now, decreasing ice levels are allowing more light to pass through the lake surface in winter months, causing warmer lake water in winter. The changes in light and temperature are altering the life cycles, habitat, behavior and stressors of fish, plankton and other organisms. These shifts, along with related changes in lake chemistry, make winter sampling more critical.

Less ice impacts organisms and humans

The extent and duration of ice coverage on the Great Lakes impacts hydropower plants, commercial shipping and the fishing industry, according to the NOAA-GLERC. It also directly affects aquatic populations. Fish habitats and migration patterns are shifting as lake ecosystems stay more active in winter months. Lake whitefish, for example, rely on thick ice cover to protect their eggs when they spawn in shallow water. Thinner ice makes them more vulnerable. Other fish, like yellow perch, hatch too early when winters are shorter and warmer, making it harder for them to survive.

Algae and plankton are also affected by temperature changes, which has a cascading effect on lake ecosystems. "The Great Lakes' food web is supported by algae grown during the winter time," says Mike McKay, Executive Director of the University of Windsor's Great Lakes Institute for Environmental Research. More plankton and algae can mean more food available for other species throughout the year. However, more active populations of certain kinds of algae in the winter can also lead to unwanted algal blooms in the summer, decreasing oxygen levels in lake water and creating toxins that are harmful for fish, people and drinking water. That's a top concern, since the Great Lakes are the drinking water source for more than 48 million people. Understanding what is happening in the lakes during the winter "provides glimpses into the future of these ecosystems," says McKay.

"We want to evaluate how the ice forms on the Great Lakes and how long it is out there," says Central Michigan University Wetland Ecology Manager Allison Kneisel. This data won't just help scientists get a clearer picture of the dynamics of the five lakes — it is also useful for understanding and predicting the health of associated wetlands, coastal ecosystems and fisheries.

Climate change makes events like the Winter Grab especially urgent. "If we are going to make an effort to delay climate change and reduce its impact, we want to know what the ice is like now and ways that it has probably already changed," Kneisel explains. "We might need to adapt our management strategies and our expectations of ecosystem services from the Great Lakes as climate changes," Ozersky adds. The coordinated winter baseline data will help scientists — and policymakers — assess and plan for continued change in the future.

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