World's largest tropical peatlands revealed to be more than 40,000 years old
A peatland complex in the Congo Basin which is known to be a globally important carbon store is twice as old as previously thought, according to a new scientific study.
An international team of researchers has shown that the tropical peatland complex, which is the world's largest, began forming about 42,000 years ago, more than 20,000 years earlier than previously thought.
Dr Greta Dargie of the University of Leeds, School of Geography, led the study. She said "These peat swamp forests are a globally important carbon store, holding the equivalent of three years of global fossil fuel emissions. We now know that they are among the most ancient tropical peatlands on the planet".
Peat is a type of soil that forms in wet environments. Made up of dead plant litter, it is an important part of the carbon cycle. While it is well known that the Congo Basin's forests store a lot of carbon in the biomass of the living plants, the work of Dr Dargie and others over the past decade has shown that Congo Basin peatlands store a similar amount of carbon out of sight below ground. This realisation has revolutionised scientific understandings of the importance of the region for the global carbon cycle.
The new study, published today in the scientific journal Environmental Research Letters, began with teams of scientists trekking through remote and inaccessible peat swamps in both the Congo and Democratic Republic of the Congo, using hand-operated equipment to collect samples of the peat from up to six metres 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 scientists 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. Prof. Ifo Suspense from the University of Marien Ngouabi, Brazzaville, in the Republic of the Congo, said: "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.
"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 of the University of Glasgow, a co-author of the study.
"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."
