What We Missed Beneath the Ice

Maggie Xenopoulos is helping scientists rethink winter, revealing the hidden season that shapes the fate of lakes.

In 2014, Dr. Xenopoulos thought she was beginning a routine study of carbon cycling in Lake Erie. Instead, she stumbled into a problem that would quietly upend how scientists understand winter itself.

For decades, lake research had treated winter as a kind of ecological pause, a frozen interval between the real work of spring and summer. But when an unusually fierce polar vortex derailed her team’s plans to conduct research aboard a Canadian Coast Guard icebreaker, Professor Xenopoulos was forced into a far riskier alternative: landing by helicopter on the frozen lake and drilling through the ice by hand.

What she found there challenged a long-standing assumption at the heart of freshwater science. Beneath the ice, the lake was not still. It was alive.

Prof. Xenopoulos, a Tier 1 Canada Research Chair in Global Change of Freshwater Ecosystems and a Biology professor at Trent University, says, “We can no longer understand or manage the Great Lakes by studying only the open-water season. Winter processes are central to ecosystem function and to climate feedback and human risk.”

At the time, though, she was simply trying to salvage a study that nearly fell apart.

A Cold Beginning

The original plan had been straightforward: sample the lake year-round from the Coast Guard ship Griffon. But that winter, ice spread thickly across the Great Lakes, and the ship was reassigned to keep commercial routes open. The research was sidelined.

“I was completely devastated,” Prof. Xenopoulos recalls.

A last-minute solution changed everything. With access to a helicopter, the team landed directly on the frozen lake. In brutal winds and biting cold, they augered through the ice and began collecting data, measuring carbon chemistry and biological activity during a season most lake scientists had long avoided.

The gamble paid off. The data revealed that Lake Erie remained far more active in winter than previously understood, continuing to cycle carbon
even under ice.

But the more profound shift was conceptual. What began as a logistical workaround became the start of a new way of seeing lakes.

The Season Scientists Forgot

The implications were hard to ignore. For generations, limnology had been built on a seasonal blind spot.

Under the ice, lakes are anything but dormant. Algae continue to grow, sometimes reaching nearly 40 percent of their summer productivity. Zooplankton, a critical food source for fish, persist as well, even in low light and cold temperatures. Meanwhile, nutrients such as nitrogen accumulate beneath the ice as microbes continue breaking down organic matter.

All of it matters. These winter dynamics do not stay confined to the colder months; they shape what happens long after the ice melts. In some lakes, strong winter growth draws down nutrients, limiting summer algal blooms. In others, nutrients build up, priming the system for explosive growth when temperatures rise. 

The lake, in other words, never really stops. 

This idea gained traction in 2016, when Xenopoulos joined an international team to synthesize winter data from lakes around the world. Their findings challenged a core assumption of the field: that winter was a biological lull. Instead, it emerged as a season of quiet but consequential activity, one that helps determine the trajectory of the entire year.

A Changing Winter

Over the past decade, Prof. Xenopoulos has helped push winter limnology from a niche pursuit into a growing research frontier. She has organized collaborative sampling efforts, contributed to international research initiatives, and trained a generation of scientists willing to venture onto frozen lakes.

That work is becoming increasingly urgent.

Across the Great Lakes, winters are changing in ways that are both visible and subtle. Ice forms later, melts earlier, and sometimes fails to form at all. Shorelines that were once protected by ice are now exposed to stronger waves and erosion. Travel routes that communities once relied on are becoming less predictable.

Beneath the surface, the changes are even more complex.

Lake ice, Prof. Xenopoulos explains, acts as a kind of master regulator. It slows biological processes, stabilizes habitats, and buffers the system
against rapid environmental change. When that buffering effect weakens, the consequences ripple outward, altering carbon cycling, microbial activity, and oxygen levels in ways that can reshape the ecosystem months later.

“Intuitively, people know winters aren’t what they used to be,” she says. “What limnology does is translate that lived experience into evidence and mechanisms that society can act on.”

What the Ice Holds

Recent research is beginning to reveal just how much winter has been doing all along. 

In a study published earlier this year, Prof. Xenopoulos and her collaborators found that lake ice itself stores biologically active forms of carbon. When the ice melts, it releases that material in a concentrated pulse, an early-season surge of energy that fuels microbes and organisms at the base of the food web.

As winters shorten, that pulse may weaken or disappear altogether.

Other work, drawing on more than two decades of data from Lake Erie, shows that the timing and duration of ice cover are linked to the size and composition of summer algal blooms. As Prof. Xenopoulos and a Ph.D. student in her lab, Claire Stevens, discovered, subtle shifts in winter conditions can echo forward into the most visible, and economically significant, events of the year.

What happens beneath the ice does not stay there.

A Fragile Future

Some consequences of winter’s decline are already impossible to ignore. In recent years, unstable ice has led to an increase in winter accidents, including a March incident near Owen Sound, where more than 20 people had to be rescued after an ice shelf broke free and drifted into Georgian Bay.

But most of winter’s changes are quieter.

They show up as variability, unpredictable seasons, shifting conditions, systems that behave in ways they didn’t before. And by the time those changes feel unmistakable, many thresholds may already have been crossed.

“Winter loss doesn’t announce itself as a crisis, it shows up as more variability, more weird years.” For Prof. Xenopoulos, that is what makes this moment so critical. “The lakes may be changing in ways that we’re not prepared for,” she says.

The Window That Remains

For all its warnings, the science also carries a sense of urgency that is not yet resignation.

There is still time to understand what winter is becoming, and to adapt.

That means paying closer attention to ice conditions, expanding year-round monitoring, and recognizing that winter is not simply a backdrop to life around the Great Lakes, but a force that shapes everything from water quality to fisheries to shoreline stability.

“The next five years are critical,” Xenopoulos says. “There is still a window to understand winter change in ways that can shape adaptation, rather than just document loss.”

After that, the patterns that once defined winter in the Great Lakes may no longer hold.

The danger is not that winter will disappear all at once. It’s that it will fade unevenly, subtly, until the systems it once regulated begin to behave in ways we no longer fully understand.

By then, the season scientists once overlooked may prove to have been the one that mattered most. “We were missing nearly half the year.”