Two large lakes in the Congo Basin are releasing carbon that has been stored underground for thousands of years, according to new research revealing a previously unknown pathway for greenhouse gases to enter the atmosphere.
Scientists studied Lake Mai Ndombe and Lake Tumba, finding that a significant portion of the carbon dioxide they emit originates from ancient peat in surrounding wetlands. The carbon is estimated to be between 2,000 and 3,500 years old.
The findings were published in Nature Geoscience. Peatlands—waterlogged ecosystems of partly decomposed plants—are among the world’s largest natural carbon stores. While they cover only about 3.8% of Earth’s land surface, they contain roughly one-third of the planet’s soil organic carbon.
The Congo Basin is home to the largest known tropical peatland complex, estimated to store about 29 billion tonnes of carbon.
Until now, scientists believed that most carbon dioxide released from lakes came from recently decomposed plant matter. This study challenges that assumption.
“These findings challenge the prevailing understanding that CO₂ emissions from pristine humic lakes are derived from modern, rapidly cycling carbon,” the researchers wrote.
The mechanism involves microbes breaking down ancient organic matter deep within the peat. The resulting carbon dioxide moves through underground water into nearby lakes, which then vent it quickly into the atmosphere. “This implies a loss pathway for peat carbon, in which microbes respire old carbon within the peat and the resulting CO₂ is transported to the lakes and outgassed,” the study explains. Once it reaches the lakes, the aged carbon escapes efficiently, making the lakes large “chimneys” for ancient peat carbon. Scientists estimate Lake Mai Ndombe alone could release over 150,000 tonnes of peat-derived carbon annually.
Although this process appears natural, it raises concerns about the stability of the Congo Basin’s peat carbon stores. If peatlands dry due to climate change or human activity, the release of ancient carbon could accelerate dramatically.
“Future peatland drying or drainage from climate or land-use change would probably accelerate this release,” the researchers warned.
The study also suggests that similar carbon pathways may exist in other peatland regions worldwide, though further research is required. “Our discovery of a natural pathway for the release of millennial-aged peat carbon links a vast reservoir of ancient carbon to the modern atmosphere,” the study concludes.
Photo from Wildlifeworks