Northern lakes face the greatest risk from warmer winters

Shorter, warmer winters are one of climate change’s most visible fingerprints. For lakes, that means later freeze-ups, earlier thaws, and thinner ice. 

A new study argues that the shifts won’t land evenly: high-latitude lakes stand to change the most, with boreal waters next in line and temperate lakes least sensitive.

“The ecology of ice-covered lakes is a bit of a black box for lake scientists,” said lead author Ted Ozersky from the University of Minnesota Duluth. 

“For a long time, we assumed that nothing interesting happened under the ice, so few studies looked at what goes on in frozen lakes.” That assumption is rapidly giving way as ice cover declines and winter ecology moves to center stage.

Why the Arctic is uniquely vulnerable

The team, spanning the U.S., Norway, and Canada, traced the outsized northern response to a simple timing mismatch: where and when sunlight shows up. 

At high latitudes, a surprisingly large portion of the year’s solar energy arrives while lakes are still under ice and snow. Near 75°N, more than half of annual sunlight reaches the surface during the ice-covered season; around 45°N, it’s roughly a quarter. 

When so much light coincides with the frozen months, even modest changes in ice duration, snow depth, or ice clarity can drastically alter how much light penetrates the water column.

“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 from 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.”

Light meets warmth – and biology responds

To move beyond anecdotes, the researchers paired models of incoming sunlight with realistic ice and snow scenarios across a sweep of latitudes, then asked how light interacts with temperature inside lakes. 

Those two drivers – illumination and heat – set the tempo for everything from algal growth to zooplankton grazing and fish foraging. 

As winters shorten, the seasonal overlap between bright conditions and hospitable temperatures grows, especially in the north. This overlap primes lakes for earlier and often stronger pulses of biological activity.

The upshot: light availability in high-latitude lakes is dramatically more sensitive to ice and snow changes than in temperate waters. A few extra centimeters of snow can dim an already light-limited under-ice habitat during weeks of 24-hour sun, suppressing photosynthesis. 

Shave a few days off ice cover during that same period and suddenly the lake is bathed in uninterrupted light, which can turbo-charge open-water productivity. Small physical tweaks, big biological consequences.

Impacts of shorter winters

Expect shifts in productivity (how much carbon the lake turns over), food-web structure (who eats whom, and when), and the timing of seasonal events – spring blooms, zooplankton hatches, fish feeding – especially at the highest latitudes. 

Because light and temperature co-vary differently with latitude, the exact trajectory won’t be uniform. Boreal lakes may see stronger, earlier spring peaks; temperate lakes will change too, but the biological “gain” on winter conditions is lower because less of their annual sunlight arrives during the ice season.

Crucially, not every change points in the same direction. Heavier snowpacks in some Arctic regions could darken under-ice habitats despite longer days, muting wintertime productivity. 

Elsewhere, less ice during endless daylight could flip the system toward higher open-water production. Either way, the calendar of growth and grazing – and the match between predators and prey – may slip out of sync.

Northern lakes in warm winters

One reason this study stands out is its scope. Many winter-lake projects zoom in on a single landscape. This team stitched together perspectives from Minnesota to boreal Québec to the high Arctic.

The research reveals a consistent latitude-dependent pattern: the farther north you go, the greater the ecological leverage of winter change. From that pattern, the experts lay out testable predictions for how lake ecosystems should respond as ice and snow evolve.

The team is now stress-testing those predictions with boots-on-ice measurements. The group is working with dozens of research teams to collect standardized observations – light profiles, snow and ice thickness, temperatures, and biological activity – across diverse frozen lakes worldwide. 

The goal is to refine models, catch regional surprises, and translate forecasts into guidance for lake managers and northern communities.

Winter isn’t an off-season

The big takeaway is easy to overlook: winter doesn’t pause lake life; it shapes it. What happens under ice sets the stage for the rest of the year, and at high latitudes, small shifts in ice and snow can have outsized effects because they coincide with so much of the annual sunlight. 

As Ozersky put it, those frozen months are no longer a “black box” – and in a warming world, paying attention to what unfolds there will be essential for protecting northern lakes and the people and wildlife that depend on them.

The study is published in the journal Ecology Letters.

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