Duluth, MN - In the world's cold and snowy regions, shorter and warmer winters are one of the most conspicuous consequences of climate change. For freshwater lakes, this means later freezing, earlier thawing, and thinner ice. A new study, published in Ecology Letters, shows that the ecological impacts of these winter changes may be most dramatic in high-latitude lakes.
"The ecology of ice-covered lakes is a bit of a black box for lake scientists," said Ted Ozersky, a University of Minnesota Duluth biologist who led the research. "For a long time, we assumed that nothing interesting happened under the ice, so few studies looked at what goes on in frozen lakes." But as ice cover declines, the winter ecology of lakes is gaining attention—and urgency. A key question scientists are now asking is: how will lakes respond to shorter, warmer winters and less ice?
The new paper, authored by researchers from the United States, Norway and Canada, shows that changes in winter ice and snow conditions will have the greatest ecological impact on Arctic lakes, followed by those in boreal and temperate areas. The reason lies in a previously unrecognized interaction between the timing of incoming solar radiation and the seasonality of ice cover.
At high latitudes, a larger share of the sun's annual light arrives while lakes are still frozen. For example, at 75°N, more than half the year's solar energy reaches the Earth's surface during the lake ice-covered period. At 45°N, that figure is closer to 25 percent. As a result, even small changes in the duration or transparency of lake ice can dramatically alter how much light reaches the water column at high latitudes.
"Here in northern Norway and in other Arctic regions, many lakes are still frozen well-into the midnight sun period, experiencing 24-hours of daylight," said co-author Amanda Poste of the Norwegian Institute for Nature Research. "In these Arctic lakes, under-ice production can contribute substantially to lake food webs, which could be threatened by predicted increases in snow cover in some regions. On the other hand, loss of ice during a period with around-the-clock daylight could lead to increased open water productivity."
The team combined models of incoming sunlight with realistic snow and ice cover scenarios across a range of latitudes. They also explored how light interacts with temperature in lakes at different latitudes. Because light and temperature are key drivers of biological productivity, understanding how these factors are changing is essential for predicting shifts in lake food webs and ecosystem functioning.
Key findings from the study include:
Light availability in high-latitude lakes is far more sensitive to changes in ice and snow conditions than in temperate lakes.
Climate change is increasing the seasonal overlap of light and warmth, especially at high latitudes, thus enhancing the potential for plant growth and animal activity.
As a result, high-latitude lakes may undergo more dramatic ecological shifts, including changes in productivity, food web dynamics and the timing of biological events.
The paper offers a new framework for understanding how climate change will affect lake ecosystems and lays out testable predictions for future research.
"Many researchers who are starting to study frozen lakes focus on just one region," said Ozersky. "Our collaboration includes researchers working on lakes in very different locations, from Minnesota to boreal Québec to the high Arctic. By working together we were able to identify this interesting large-scale pattern."
The study underscores that winter plays a key role in shaping lake ecosystems, and that changes that happen during the ice cover period can have powerful and lasting effects, especially in northern lakes. The authors are now working with dozens of research groups around the world to collect standardized observations from diverse ice-covered lakes to test and refine the model's predictions.
The Ecology Letters paper, titled "Impacts of Changing Winters on Lake Ecosystems will Increase with Latitude" , was co-authored by Ted Ozersky (University of Minnesota Duluth), Amanda Poste (Norwegian Institute for Nature Research), Milla Rautio (Université du Québec à Chicoutimi), and Eva Leu (Akvaplan-NIVA).
