Jasmine Saros has visited West Greenland every summer since 2011. Saros, professor of lake ecology at the University of Maine, travels north each year to collect data on the region’s fresh waters. In 2022, she conducted her usual rounds of sampling and assessment on the 10 representative lakes that she and her colleagues regularly visit. Everything has generally gone according to plan – changing slowly with climate change, but seemingly as it has been for over a decade. Then suddenly, that wasn’t the case anymore.
The following year, in the summer of 2023, Saros returned to find the familiar lakes completely transformed. “You could see it right away,” she said. The bodies of water had gone from crystal blue – their rocky bottoms as visible as if you were looking through glass – to soaked tea brown. At first, scientists thought it might have been one lake, then two, then three. Until “every lake we went to changed that way,” Saros says. “There was this major transformation that happened in all the lakes on the landscape,” she says. Popular science. “It was truly astonishing.
Historically, West Greenland is a relatively arid expanse of tundra. In summer, the thawed landscape is covered in low vegetation, with permafrost still frozen beneath the ground. The region is dotted with thousands of lakes. In the Saros study area, she and her co-researchers estimate there are 7,486. She expects most, if not all, to have changed from blue to brown.
The color change isn’t just aesthetic. This is a sign that the fundamental ecology of the lakes has changed over the course of a single year, according to a study published on January 22 in the magazine Proceedings of the National Academy of Sciences. Among the changes: lakes lost 90% of their microbial biodiversity, gained 1,000% more dissolved iron and went from absorbing carbon dioxide to emitting it, moving from sink to source, according to the new research led by Saros.
The transformation, caused by a particularly warm and humid autumn, could be permanent. It’s an illustration of what happens when climate tipping points – often discussed in the abstract, as something we’re ever-approaching – actually happen and an ecosystem tips over the proverbial cliff. And it’s a warning of what could happen everywhere else. “We focus on Arctic lakes because they are powerful sentinels of climate change. They tend to show changes before other lake ecosystems,” says Saros. The Arctic is particularly rapid warming and climate is the main driver of change there, because human density is low and development is low. But nowhere is safe.
In Greenland, scientists responded to newly browning lakes by gathering all the data they could. As usual, they walked to their study sites with heavy backpacks full of equipment and ventured out to each lake aboard an inflatable raft. They collected water from different depths, captured plankton, used sensors to record temperature and pH, and even measured the lake’s light absorption. Back in the laboratory, they analyzed their samples and checked for the presence of dissolved organic matter, metals and living organisms.
They discovered profound differences between the water of 2023 and that of previous years. There was a lot more dissolved organic matter – think soil, decaying soil, and plant detritus infused into a broth. Iron levels increased by two orders of magnitude, and other metals like aluminum and cobalt were also more abundant. There were far fewer bacterial taxa and far more algae. Photosynthesis declined, as the deeper areas of each lake became lifeless, deprived of light. Methane jumped 72% and lakes became new sources of summer greenhouse gas emissions, releasing more than four times more carbon dioxide than before, while absorbing less.
To determine why, researchers studied years of weather and climate data. They settled over a two-month period in the fall of 2022, when Greenland experienced record heat and precipitationresulting from several consecutive operations atmospheric rivers. During the heatwave and excessive rain, much of the permafrost thawed, releasing a large volume of soil-bound organic matter and metals. “This extreme fall season has essentially led to a significant discharge of these materials into the lakes,” says Saros. The lakes grew larger and became more connected to each other, mixing and spreading change far and wide. Additional heavy rain and heat in July 2023 added to the pileup. Satellite images suggest the change was not specific to lakes. With the addition of heat and water, the earth also changed, becoming significantly greener.
The browning of lakes is not a new phenomenon. This has happened many times in Earth’s history in response to climate change or other changes in local conditions. But typically it would happen much more slowly, over centuries or more. “In the northern United States, for example, it would take about 1,000 years for this type of color change to occur naturally,” says Saros. “I never thought such a radical change could happen in less than a year,” she says. A rapid and related change was noted in some Alaskan riversalso in response to thawing permafrost. It is a high-speed ecological modification.
In September 2003, Greenland experienced a similar influx of precipitation. But the heat that accompanied it was less extreme. As a result, a greater proportion of moisture fell as snow, less permafrost thawed and the lakes have not radically changed state. Climate change is making heat waves and atmospheric rivers more common in the Arctic. Models predict anywhere 50 to 290% more concentrated precipitation events in Greenland by 2100.
It’s not clear what conditions or how long it would take for the lakes to return to their previous state, Saros says. Perhaps a series of dry years could help, with the sun bleaching the organic matter. But, at the same time, dry weather means more evaporation and less removal of contaminants. “It’s hard to predict,” she notes. Still, given our current climate trajectory, she doesn’t expect to see blue lakes again anytime soon. “I think (the change) will probably persist,” Saros says. She and her co-authors will continue to monitor bodies of water, to learn what the future holds and in hopes that their recovery is possible.
But for now, the consequences are being felt for people in the present. Some Greenlandic communities rely on lakes for their drinking water. Changes in the ecosystem could pose risks to human health, such as metal toxicity. There are ways to treat and filter water to mitigate damage, but all of this requires investment in infrastructure. “We’ve been sharing our data and talking to various people in the community,” Saros says, but she’s not sure yet exactly what they plan to do.
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