The central Congo Basin contains the world’s most extensive tropical peatland complex, spanning 16.7 million hectares. Until now, radiocarbon dating of ancient peats has been limited to 14 samples with poor coverage, and suggested that peat typically initiated during the Holocene. New research indicates that peat initiated in the central Congo Basin at multiple locations in the Late Pleistocene. The oldest date determined by the authors is 42,300 years before present, making this one of the world’s oldest extant tropical peatlands, and twice as old as previously believed.
Swamp forest in the Democratic Republic of the Congo. Image credit: Greta Dargie.
The central Congo Basin straddles the equator, containing 360,000 km2 of wetland that is shared between the Republic of the Congo and the Democratic Republic of the Congo.
Of this wetland area, an estimated 167,600 km2 is swamp forest underlain by peat deposits, with a median thickness of 1.7 m.
These peatlands are some of the most carbon-dense ecosystems on Earth, storing an average of 1712 Mg C ha−1, with a total of 29 Pg C−1 stored in the peat.
However, research into the establishment and development of this large carbon stock, including the dynamics of peat initiation and expansion across the basin, is in its early stages.
“These peat swamp forests are a globally important carbon store, holding the equivalent of three years of global fossil fuel emissions,” said University of Leeds researcher Greta Dargie.
“We now know that they are among the most ancient tropical peatlands on the planet.”
The study began with research teams trekking through remote and inaccessible Congolese peat swamps, using hand-operated equipment to collect samples of the peat from up to 6 m below the forest floor.
Back in the laboratory, tiny amounts of the peat were dated using radiocarbon, to determine when the peat began to form in each sampled location.
Over a period of 10 years the researchers collected and dated more than 50 cores from across the central Congo Basin, from which they were able to build up a picture of the development of the peatlands through time.
It is not just the great age of the peatlands which came as a surprise to the scientists.
“One of the most unexpected findings which came from our new data is that some of the older peatlands in central Congo Basin began forming during periods of the past when we think that the regional climate was a lot drier than it is today,” said University of Marien Ngouabi’s Professor Ifo Suspense.
“Our previous working hypothesis was that the peat began forming in response to a wetter climate at the start of the Holocene epoch, around 12,000 years ago.”
“But we now know that factors other than climate must have made the soils wet and waterlogged enough for peat to form.”
“This raises questions about how the peatland landscape, and the large amount of carbon it stores, will respond to 21st century climate change.”
The Congo Basin peat swamps provide important resources for local communities such as fish, bushmeat and building resources.
Their remoteness means that the swamps are important refuges for species such as forest elephants, dwarf crocodiles, lowland gorillas and bonobo chimpanzees.
Compared to many tropical regions, the Congolese peatlands have largely escaped threats such as deforestation and drainage, although the drive to improve local livelihoods and extract resources such as timber and oil for export could potentially come into conflict with the goals of biodiversity and carbon conservation.
“The great age of the peatlands drives home how valuable they are,” said Dr. Pauline Gulliver, a researcher at the University of Glasgow.
“There has been peat here, quietly drawing carbon out of the atmosphere, and safely storing it for at least forty millennia.”
“The peat can’t be replaced on any timescale that’s meaningful to society.”
“Where peatlands have been disturbed by people around the planet, they have released huge amounts of carbon to the atmosphere, exacerbating global warming.”
“The carbon in the Congo Basin peatlands requires careful treatment so that the same thing does not happen here.”
The findings were published in the journal Environmental Research Letters.
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Greta C. Dargie et al. 2025. Timing of peat initiation across the central Congo Basin. Environ. Res. Lett 20, 084080; doi: 10.1088/1748-9326/ade905
