Thousands of lakes in Greenland have crossed a tipping point

West Greenland is renowned for its blue lakes that supply drinking water and help sequester atmospheric carbon. 

However, following two months of record heat and heavy rainfall in fall 2022, researchers discovered that an estimated 7,500 of these lakes turned brown, began emitting carbon, and suffered a decline in water quality. 

This dramatic change, reported in a study published in the Proceedings of the National Academy of Sciences (PNAS), underscores how extreme climate events can push Arctic lakes past critical tipping points.

Unprecedented changes in a short time

Led by Fulbright Distinguished Arctic Scholar Jasmine Saros of the University of Maine Climate Change Institute, an international team investigated the rapid transformation of these lakes. 

By July 2023, less than a year after the extreme fall weather, the physical, chemical, and biological properties of the lakes had undergone widespread alterations – changes that would normally unfold over centuries.

“The magnitude of this and the rate of change were unprecedented,” said Saros, who also serves as a professor of paleolimnology and lake ecology at UMaine.

How climate extremes affected Greenland lakes

Greenland typically sees snowfall in the fall, but record temperatures turned precipitation into rain. This shift, combined with the heat, caused permafrost – frozen soil rich in organic carbon and minerals – to thaw. 

As rainwater washed through the thawing ground, it carried an abundance of carbon, iron, magnesium, and other elements into the lakes, turning their waters brown.

The influx of dissolved organic carbon and nutrients fueled bacterial growth, affecting the lakes’ taste, odor, and color. Increased metals in the water raised health concerns as well.

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

Such changes not only impact water quality but also have broader implications for local communities relying on these lakes.

Disrupted ecosystems and the carbon cycle

As the lakes turned brown, water transparency declined, reducing light penetration and altering plankton dynamics. Reduced light hindered phytoplankton that normally absorb carbon dioxide through photosynthesis, while organisms that break down organic matter increased. 

This shift transformed the lakes from carbon sinks into significant sources of carbon dioxide, with emissions rising by 350%.

“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,” Saros said.

This change in plankton behavior and carbon cycling has major ramifications for the Arctic carbon budget and local biodiversity.

The role of atmospheric rivers

The researchers pinpointed atmospheric rivers – long, narrow streams of water vapor – as the likely cause of the extreme weather. These phenomena brought record-breaking heat and rainfall to the region. 

The National Oceanic and Atmospheric Administration (NOAA) predicts that atmospheric rivers will become much more frequent in Greenland and other parts of the world by the end of the century, potentially leading to more events like those of fall 2022.

Will the lakes of Greenland recover?

The abrupt transformation raises pressing questions about recovery: Will the lakes return to their former blue state, or will changes persist? 

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

Ongoing monitoring and additional research are crucial. The team’s work relied on long-term observations, including annual water sampling and year-round remote sensors, which allowed them to capture the rapid changes caused by the extreme climate event.

“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.” 

Future research on Greenland lakes

The study was made possible through extensive collaboration among researchers from UMaine, NOAA, and various international institutions, as well as contributions from numerous PhD students. 

This collective effort has provided valuable insights into how extreme weather events can drastically alter lake ecosystems and carbon dynamics.

As atmospheric rivers become more frequent, understanding their impact on Arctic lakes like those in West Greenland is essential. 

Further research into how these lakes recover and how similar events affect other regions will help scientists develop strategies to mitigate and adapt to the impacts of climate change.

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