Climate sciences: Past drying in Congo peatlands caused carbon release

A drying climate in the central Congo Basin around 5,000–2,000 years ago caused peat to decompose and release carbon, a study in Nature suggests. The finding highlights how changing climates can affect the carbon storage capabilities of these wetlands.

The forested swamps of the central Congo Basin are the world's largest tropical peatland complex, storing around 30 billion metric tonnes of carbon (28% of Earth's tropical peat carbon stock). However, little is known about the history of this ecosystem. Understanding this history may help us to determine how vulnerable these peatlands are to climate change and inform policies to assess the risks posed by activities such as logging, oil exploration and agriculture.

To evaluate the response of the central Congo peatlands to past climate changes, Yannick Garcin and colleagues analysed peat cores from a large basin in the Republic of the Congo. They find that peat accumulation began at least 17,500 years ago, and discover that less peat accumulated between around 7,500 to 2,000 years ago and the peat is much more decomposed compared with older and younger peat. Analyses of plant material indicate that there was a period of drying over this time, particularly between 5,000 and 2,000 years ago. The authors propose that the drying climate caused the water table to drop, triggering peat decomposition, including the loss of peat carbon accumulated prior to the onset of the drier conditions. However, the peatland reverted back to a carbon sink during a recovery phase over the past 2,000 years.

These results suggest that this region may be involved in a positive feedback in the global carbon cycle and if anthropogenic climate change results in more droughts in the congo basin, this could lead to the release of further carbon from peat to the atmosphere the authors note.