Extreme climate pushed thousands of lakes in West Greenland 'across a tipping point,' study finds

West Greenland is home to tens of thousands of blue lakes that provide residents drinking water and sequester carbon from the atmosphere. Yet after two months of record heat and precipitation in fall 2022, an estimated 7,500 lakes turned brown, began emitting carbon and decreased in water quality, according to a new study.

Led by Fulbright Distinguished Arctic Scholar and University of Maine Climate Change Institute Associate Director Jasmine Saros, a team of researchers found that the combination of extreme climate events in fall 2022 caused ecological change that "pushed Arctic lakes across a tipping point," they wrote in a paper published in the the Proceedings of the National Academy of Sciences?(PNAS). By July 2023, less than one year later, the physical, chemical and biological properties of these lakes were altered, a widespread transformation that typically occurs over hundreds of years, Saros said. Their results were shared with nearby communities.

Greenland normally experiences snow in the fall, but the spike in temperatures caused the precipitation to fall as rain instead, according to the study. The heat also caused permafrost — frozen soil that stores a significant amount of organic carbon — to thaw, releasing an abundance of carbon, iron, magnesium and other elements. As rain fell in record amounts, it washed these newly exposed metals and carbon from soil into lakes across Greenland's western region, turning them brown.

Saros, also a professor of paleolimnology and lake ecology with UMaine's School of Biology and Ecology, said the rapid alteration in West Greenland's lakes contrasts with the slow, multi-decade-long browning experienced in lakes across the Northern Hemisphere, including those in Maine.

"The magnitude of this and the rate of change were unprecedented," Saros said.

The influx of dissolved organic carbon and nutrients from the permafrost can promote bacteria growth and produce an undesirable taste and odor in the water, in addition to altering color, Saros said. Increased exposure to metals released from permafrost can also cause health problems. By identifying the type and quantity of organic and inorganic materials entering the lakes following the climate extreme events, residents in the surrounding area can better evaluate how to treat their water.

"The increased dissolved organic material can interact with drinking water treatment processes to produce chlorination byproducts called trihalomethanes, which may be carcinogenic," Saros said.

With altered physical and chemical properties, the lakes became more opaque and less light was able to penetrate their surface. The reduction in light decreased the biodiversity of plankton, which had significant ramifications for the region's carbon cycle. Researchers found a decrease in phytoplankton that absorb carbon dioxide from the atmosphere through photosynthesis, and an increase in plankton that break down and release carbon. Instead of sequestering carbon dioxide in the summer, the lakes have become a source of it, with a 350% increase in the flux of this greenhouse gas from them.

"The likely explanation is that so much organic carbon mobilized from the landscape into the surface water, and the organic carbon was available for aquatic organisms to use," Saros said. "Because the lakes turned so brown, it reduced the light coming into the system, which tends to favor organisms that use organic carbon pathways instead of photosynthesis."

Researchers concluded that the rise in heat and precipitation was caused by several atmospheric rivers. According to the National Oceanic and Atmospheric Administration (NOAA), an atmospheric river is a long, narrow column of water vapor that produces intense rain or snow when it makes landfall. They affect much of the world, and existing climate models predict that by the end of the century, they will become 50-290% more frequent in Greenland, western North America, east Asia, western Europe and Antarctica.

Saros said additional research and monitoring could help determine how these lakes may recover, providing greater insight into lake dynamics in the region. Further studies can also help scientists examine browning lakes across the Northern Hemisphere, how they may recover and potential treatment and intervention.

"It was such an overwhelming climate force that drove all the lakes to respond in the same way," Saros said. "When it comes to recovery, will it be the same across lakes or different?"

The study was made possible through extensive data collection obtained through annual water sampling and remote sensors in the lakes that operate year-round.

"Our study demonstrates the power of long-term observation. I've been working in this area since 2013, and have worked on many projects here. But in the background, my colleagues and I have been trying to maintain a consistent data set of observations," Saros said. "That's how we were able to capture and quantify the effects of this extreme climate event."

In addition to Saros, UMaine Ph.D. students Václava "Vendy" Hazuková, Grayson Huston, Avery Lamb and Guillaume Bourdin co-authored the study.

Other co-authors include Sean Birkel, Maine state climate scientist and assistant professor with 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 said Binbin and Northington were former postdoctoral associates at UMaine.

"Many Ph.D. students were involved in this work, and were totally instrumental in this work," she said.