Jasmine Saros has visited West Greenland every summer since 2011. Saros, a professor of lake ecology at the University of Maine, travels north annually 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 her and her colleagues routinely visit. Everything was generally as expected–slowly shifting in accordance with climate change, but outwardly appearing as it had for more than a decade. Then suddenly, it wasn’t.
The next year, summer 2023, Saros returned to find the familiar lakes utterly transformed. “You could see it right away,” she says. The water bodies had gone from crystal clear and blue–their rocky bottoms as visible as if looking through glass–to a steeped tea-brown. At first, the scientists thought perhaps it was just one lake, then two, then three. Until “every single lake we went to had changed in this way,” Saros says. “There was this major transformation that occurred across all the lakes in the landscape,” she tells Popular Science. “It was really astonishing.”
Historically, West Greenland is a relatively arid expanse of tundra. In summer, the thawed landscape is covered in low-lying vegetation, with permafrost sitting still-frozen beneath the soil. The region is dotted with thousands of lakes. In Saros’ study area, she and her co-researchers estimate there are 7,486. She expects that most, if not all, have turned from blue to brown.
The color shift isn’t just aesthetic. It’s a sign that the lakes’ fundamental ecology was altered over the course of a single year, according to a study published January 21 in the journal Proceedings of the National Academy of Sciences. Among the changes: the lakes lost 90% of their microbial biodiversity, gained 1,000% more dissolved iron, and went from absorbing carbon dioxide to emitting it–shifting from sink to source, per the new research, led by Saros.
The transformation, brought about by one especially warm and wet fall, 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 come to pass, and an ecosystem topples over the proverbial cliff. And it’s a warning of what could happen everywhere else. “We focus on lakes in the Arctic because they are such great sentinels of climate change. They tend to show change before other lake ecosystems do,” says Saros. The Arctic is warming especially fast and climate is a primary driver of change there, as there’s low human density and little development. But nowhere is immune.
In Greenland, the scientists responded to the newly brown lakes by amassing all the data they could. As usual, they hiked to their study sites carrying heavy backpacks full of equipment and ventured out on each lake in an inflatable raft. They scooped up water from different depths, netted for plankton, used sensors to record temperature and pH, and even measured the lake’s light absorbance. Back in the lab, they analyzed their samples and checked for dissolved organic matter, metals, and living organisms.
They found profound differences between the 2023 water and prior years. There was far more dissolved organic matter–think soil, decaying muck, and plant detritus infused into a broth. Iron levels shot up by two orders of magnitude, and other metals like aluminum and cobalt were also more abundant. There were far fewer bacterial taxa present, and far more algae. Photosynthesis decreased, as the deeper zones of each lake became lifeless deprived of light. Methane jumped by 72%, and the lakes were newly sources of summertime greenhouse gas emissions, spitting out more than four times as much carbon dioxide as before, while taking in less.
To determine why, the researchers surveyed years of weather and climate data. The homed in on a two month period in the fall of 2022 when Greenland experienced record heat and rainfall, resulting from multiple back-to-back atmospheric rivers. During the heatwave and excess rains, lots of permafrost thawed, releasing a large volume of organic matter and metals bound in the soil. “This extreme autumn season essentially led to a big flushing of that material into lakes,” says Saros. Lakes expanded and became more connected to each other, intermixing and spreading the change far and wide. Additional heavy rains and heat in July 2023 added to the pile-on. Satellite imagery suggests the change wasn’t specific to the lakes. With the added heat and water, the land changed too, becoming measurably greener.
Lake browning is not a new phenomenon. It’s happened numerous times in Earth’s history in response to climate shifts or other changes in local conditions. But generally it would unfold much more slowly, over centuries or longer. “In the northern part of the United States, for example, it would take about 1,000 years for that kind of change in color to happen naturally,” Saros explains. “I never thought such a dramatic change could happen in less than a year,” she says. A related, rapid change has been noted in some of Alaska’s rivers, also in response to permafrost thaw. It’s ecological modification at hyper speed.
In September 2003, Greenland experienced a similar influx of precipitation. But the accompanying warmth was less extreme. As a result, a higher proportion of the moisture fell as snow, less permafrost thawed, and the lakes didn’t dramatically shift states. Climate change is making both heatwaves and atmospheric rivers more common in the Arctic. Models predict anywhere from 50 to 290% more of the concentrated rainfall events in Greenland by 2100.
It’s unclear what conditions or how much time would be needed for the lakes to revert back to their former state, says Saros. Perhaps a series of dry years might help, with the sun bleaching the organic matter. But, at the same time, dry weather means more evaporation and less flushing out of contaminants. “It’s hard to predict,” she notes. Yet on our current climate trajectory, she doesn’t expect to see the lakes blue again anytime soon. “I think [the change] is likely to persist,” Saros says. She and her co-authors will continue keeping tabs on the water bodies, to learn what the future holds and in the hope recovery is possible.
For now though, the consequences are unfolding for people in the present. Some Greenlandic communities rely on lakes for their drinking water. The ecosystem changes could pose health risks to humans, like metal toxicity. There are ways of treating and filtering water to mitigate the harms, but all of that requires infrastructure investment. “We shared our data and talked to various people in the community,” says Saros, but she’s not yet sure what they plan to do.
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