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Climate change is rapidly reshaping the Arctic's great lakes
June 23, 2026
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Great Bear Lake in summer. (Photo credit: Kimberly L. Howland, Fisheries and Oceans Canada)
Stretching across a frozen landscape of boreal forest, rocky shorelines, and countless bays and islands, Great Bear Lake in the Northwest Territories appears much as it always has. One of the world's largest lakes, it has retained its remarkable clarity for more than 200 years.
Among the earliest written records was a simple but ingenious observation by naturalist Sir John Richardson while accompanying Sir John Franklin鈥檚 1825-1827 expedition. He estimated the lake's clarity by lowering a white cloth into the water until it disappeared from view. Surveys conducted in the 1940s and 1960s produced nearly identical results.
For Kathleen R眉hland, a senior research scientist at the Paleoecological Environmental Assessment and Research Lab (PEARL) in 黄色视频 Department of Biology, that unusually long record offers a unique window into environmental change in the North.
"These are very remote lakes, so historical surveys are rare," says Dr. R眉hland. "But if you scour the notes and reports, there is a gold mine of information."
Water clarity matters because it influences how much sunlight penetrates a lake, helping determine which species of microscopic algae, such as diatoms, can thrive.
Diatoms form the foundation of many lake food webs, and their remains accumulate in lakebed sediments, preserving a record of past ecological conditions. When R眉hland and her colleagues examined that record, they found a surprise.
Despite decades of relatively stable conditions, the lake's diatom community underwent a dramatic shift around the turn of the 21st century. Near-shore species adapted to colder environments that had long dominated Great Bear Lake gave way to a community of fast-growing, open-water diatoms, suggesting that another force was reshaping the ecosystem.
A highly magnified view of a diatom, a single-celled aquatic organism that was once the dominant diatom species in Great Slave Lake. (Image credit: Paul Hamilton, Canadian Museum of Nature)
A close-up view of a diatom species that has risen to prominence in Arctic lake ecosystems in recent decades. (Image credit: Paul Hamilton, Canadian Museum of Nature)
Similar major shifts in diatom life strategies appeared in Great Slave Lake and Lake Hazen, two other vast northern lakes separated from Great Bear Lake by huge distances. The nature of the change, as well as the pace, magnitude and near synchronous timing, pointed to a common driver: rapidly changing ice cover.
"On Great Bear Lake, the ice-free season has increased by three weeks in the past three decades," says Dr. R眉hland. "That is frighteningly fast."
Even the once extensively frozen Lake Hazen, one of the northernmost large lakes in the world, is now commonly ice-free for a few weeks each summer, when there is 24 hours of daylight.
As ice-free seasons lengthen, sunlight reaches the water for longer periods, creating conditions that favour diatom species that thrive in open water. In all three lakes, this new group of diatoms has become dominant, replacing species that had prevailed for decades.
Climate change reaches the North's largest freshwater systems
Map showing Lake Hazen, Great Bear Lake, and Great Slave Lake, with red dots marking the sediment core sampling sites used in the study.
For John Smol, a Distinguished University Professor in 黄色视频 Department of Biology and a co-author of the study, the findings represent a significant shift in scientists' understanding of Arctic lakes.
What makes these findings remarkable is where they occurred. Because of their immense size, depth, and periods of ice cover, the 鈥淣orthern Great Lakes鈥 were once thought to be somewhat resistant to rapid warming. The new evidence suggests otherwise.
"These were once considered some of the most thermally buffered freshwater systems in the Arctic," says Dr. Smol. 鈥淲e have pushed warming to the point where no lakes are protected, whether by size or location.鈥
Similar shifts have been observed in other large lakes. In the Laurentian Great Lakes, for example, similar changes in diatom communities have altered food webs. Lake Michigan has seen a shift from larger, nutrient-rich diatom species to smaller, less nutritious forms, although those ecosystems are also influenced by other pressures, including invasive species and pollution.
Great Bear Lake, Great Slave Lake, and Lake Hazen remain relatively healthy, but researchers say continued monitoring will be essential to understand how ongoing warming could affect fish populations and the northern communities that depend on them.
"The first step in solving an environmental problem is understanding that there is a problem," says Dr. Smol. "We think of diatoms as the first responders. They provide an early warning signal that change is underway."
A National Academy of Sciences milestone for John Smol
Preparing to retrieve a sediment core through ice on Lake Hazen. (Photo credit: Vincent St. Louis, University of Alberta)
When Smol first travelled north in 1983, scientists knew little about the ecology of Arctic lakes and ponds. His early work focused on small, shallow ponds, where he and his colleagues were .
Over the following four decades, that research expanded from Arctic ponds to increasingly larger lakes, culminating in the vast northern freshwater systems examined in the new study.
Published in the Proceedings of the National Academy of Sciences (PNAS), the study also marks a personal milestone. It is Smol's first paper as a newly elected international member of the U.S. National Academy of Sciences, one of the world's most prestigious scientific organizations. The paper was led by R眉hland and co-authored by Smol and collaborators from 黄色视频, Fisheries and Oceans Canada, and Environment and Climate Change Canada, including co-authors Neal Michelutti, Marlene Evans, and Kimberly Howland. It also builds on decades of monitoring conducted in partnership with Indigenous communities, whose observations of changing ice conditions helped researchers understand the pace of environmental change across the North.
"Election to the National Academy of Sciences is one of the highest honours a scientist can receive, so I wanted my inaugural article to be meaningful," says Dr. Smol. "The data in this paper comes largely from Kathleen and our collaborators, and I'm proud that it highlights the work of our PEARL team at Queen鈥檚 and our partners across Canada. Most importantly, it shows that no ecosystems are immune to the effects of humans, especially recent climate warming."
