Following a period of unprecedented heat and rainfall in the fall of 2022, around 7,500 lakes in West Greenland turned brown, started emitting carbon, and experienced a decline in water quality within a year. The increase in temperatures led to precipitation falling as rain rather than snow. Additionally, the heat caused permafrost to melt, releasing significant amounts of carbon, iron, magnesium, and other substances that were subsequently washed into the lakes. Researchers observed a reduction in phytoplankton—which typically absorb carbon dioxide through photosynthesis—and a rise in plankton that decompose and discharge carbon. As a result, instead of acting as carbon sinks during the summer, the lakes became sources of carbon dioxide, with a dramatic increase of 350% in emissions.
West Greenland boasts countless blue lakes that provide drinking water for locals and help sequester carbon from the atmosphere. However, after encountering two months of record-setting heat and rain in the fall of 2022, an estimated 7,500 lakes turned brown, started releasing carbon, and saw a drop in water quality, according to a recent study.
Research led by Fulbright Distinguished Arctic Scholar and Associate Director of the University of Maine Climate Change Institute, Jasmine Saros, showed that the combination of extreme climate events in fall 2022 led to ecological changes that “pushed Arctic lakes across a tipping point,” as detailed in a paper released in the Proceedings of the National Academy of Sciences?(PNAS). By July 2023, which is less than a year later, the lakes’ physical, chemical, and biological characteristics had changed significantly—transformations that usually take hundreds of years to occur, according to Saros. These findings were shared with nearby communities.
Typically, Greenland experiences snowfall in the fall; however, warmer temperatures resulted in rain instead, the study revealed. This warmth also caused permafrost—frozen ground that stores a considerable amount of organic carbon—to melt, releasing copious amounts of carbon, iron, magnesium, and other elements. Record rainfall washed these released metals and carbon from the soil into the lakes, resulting in their brown coloration.
Saros, who is also a professor of paleolimnology and lake ecology at UMaine’s School of Biology and Ecology, noted that the swift changes observed in the lakes of West Greenland stand in stark contrast to the gradual browning seen in lakes across the Northern Hemisphere, including those in Maine.
“The scale and speed of this change were unprecedented,” Saros stated.
The increase in dissolved organic carbon and nutrients from the melting permafrost could encourage bacterial growth, leading to unpleasant tastes and odors in the water, as well as altering its color, Saros explained. Additionally, the higher levels of metals released from permafrost could pose health risks. By determining the types and amounts of organic and inorganic materials entering the lakes after these climate-related events, local residents can better assess water treatment methods.
“The rise in dissolved organic materials can interact with drinking water treatment systems, forming chlorination byproducts known as trihalomethanes, which may be carcinogenic,” Saros cautioned.
Changes in the lakes’ physical and chemical properties led to increased opacity, reducing the amount of light able to penetrate their surfaces. This drop in light reduced the diversity of plankton, which had substantial effects on the carbon cycle in the region. Specifically, researchers found fewer phytoplankton that sequester carbon dioxide through photosynthesis, while plankton that break down and release carbon increased. Instead of capturing carbon dioxide during the summer months, the lakes became sources of it, with emissions increasing by 350%.
“The likely reason for this is that so much organic carbon was released from the landscape into the water, making it accessible for aquatic organisms,” Saros noted. “Because the lakes turned so brown, it limited the light that entered the system, which tends to favor organisms that rely on organic carbon instead of photosynthesis.”
Researchers concluded that the increase in temperature and rainfall was influenced by several atmospheric rivers. According to the National Oceanic and Atmospheric Administration (NOAA), atmospheric rivers are narrow bands of water vapor that bring heavy rain or snow when they reach land. They affect many regions globally, and climate forecasts suggest that by the century’s end, they could become 50-290% more frequent in Greenland, parts of North America, East Asia, Western Europe, and Antarctica.
Saros commented that further research and monitoring could shed light on how these lakes might recover, providing deeper insights into the dynamics of lakes in the area. Additional studies can also assist scientists in understanding browning lakes throughout the Northern Hemisphere and determining their recovery processes as well as possible treatment and intervention methods.
“This extreme climate phenomenon overwhelmingly affected all the lakes similarly,” Saros remarked. “When it comes to recovery, will it be uniform across all lakes, or will it differ?”
The research benefited from comprehensive data collection achieved through continuous water sampling and remote sensors operating year-round in the lakes.
“Our study highlights the importance of long-term observation. I’ve been engaged in research in this region since 2013, working on numerous projects here. Behind the scenes, my colleagues and I have been striving to maintain a consistent dataset of observations,” Saros explained. “This is how we were able to capture and quantify the impacts of this extreme climate event.”
Alongside Saros, University of Maine Ph.D. candidates Václava “Vendy” Hazuková, Grayson Huston, Avery Lamb, and Guillaume Bourdin contributed to the study.
Other co-authors include Sean Birkel, Maine’s state climate scientist and assistant professor at the Climate Change Institute and University of Maine Cooperative Extension; Robert Northington from Elizabethtown College in Pennsylvania; Ryan Pereira from Heriot-Watt University in Edinburgh; Binbin Jiang from Zhejiang University of Science and Technology in China; and Suzanne McGowan from the Netherlands Institute of Ecology. Saros mentioned that Binbin and Northington were former postdoctoral researchers at UMaine.
“Numerous Ph.D. students played essential roles in this research,” she added.
