Ancient Carbon Release: Congo Basin Peatlands Shifting from Sink to Source

The vast, remote Congo Basin is revealing a surprising and potentially concerning shift in its carbon cycle. Recent research indicates that ‘blackwater’ lakes and rivers within the region are releasing ancient carbon into the atmosphere, challenging previous assumptions about these ecosystems as reliable carbon sinks. This discovery raises questions about the stability of the Congo Basin’s peatlands – the largest in the world – and their role in regulating global climate.

For years, scientists believed the carbon stored within the Congo Basin’s peatlands remained safely locked away underground. Peatlands are essentially waterlogged areas where partially decayed plant matter accumulates over millennia. This creates an oxygen-depleted environment that slows decomposition, effectively trapping carbon. Although, new findings suggest that this isn’t always the case, and that some tropical peatlands may be transitioning from absorbing more carbon than they release to doing the opposite.

Ancient Carbon’s Unexpected Journey

The research, published February 23 in Nature Geoscience, centers on the Cuvette Centrale, a 56,000-square-mile region spanning the Democratic Republic of the Congo. This area holds Earth’s largest known tropical peatland complex. Specifically, the study focused on two large blackwater lakes – Lake Mai Ndombe and Lake Tumba – and the Ruki River, which flows through the region and eventually into the Congo River. These bodies of water get their dark color from high concentrations of decaying plant debris, also known as dissolved organic carbon.

Blackwater systems are naturally rich in carbon dioxide (CO2), both from the decaying organic matter and direct emissions from surrounding swamps and forests. What surprised researchers, led by Travis Drake, a carbon biogeochemist at the Swiss Federal Institute of Technology Zurich (ETH Zurich), was the age of the carbon being released. Traditionally, it was assumed this CO2 was relatively modern, originating from recently decayed plant life. Instead, the team found that a significant portion – between 2,170 and 3,500 years old – was ancient peat carbon.

“We were very surprised because we fully expected the carbon dioxide to be modern,” Drake told Live Science. The team’s findings suggest that microbes within the region are breaking down this ancient peat carbon into CO2 and methane, which then bubbles up into the lakes and rivers and ultimately escapes into the atmosphere. This process challenges the long-held view of tropical peatlands as stable, long-term carbon stores.

Challenges in the Field and the Significance of the Findings

Gathering data in the Cuvette Centrale presented logistical challenges. Researchers accessed Lake Mai Ndombe by small boats, a precarious undertaking given the strong winds. The team conducted three research trips over the past four years, meticulously measuring sediments, greenhouse gases, dissolved organic carbon, and inorganic carbon in the water samples. They then used high-precision spectrometry to differentiate between modern carbon from plants and older carbon from the peat deposits.

The Cuvette Centrale is estimated to hold approximately one-third of the world’s tropical peatland carbon – around 33 billion tons (30 billion metric tons). The implications of releasing even a fraction of this stored carbon are substantial. While the study acknowledges the possibility that this carbon release is a natural process linked to the formation of new peat deposits, it also raises concerns that climate change may be destabilizing these ancient deposits.

What Does This Mean for the Climate?

The study highlights a critical vulnerability. If the region experiences increased drought, as predicted by many climate models, the release of ancient carbon could accelerate, potentially transforming the Congo Basin’s peatlands from a carbon sink into a major carbon source. This would exacerbate climate change, creating a feedback loop where increased carbon emissions lead to further warming and drying, accelerating the release of even more carbon.

It’s important to note that the study doesn’t definitively prove a widespread destabilization of the peatlands is underway. Drake and his colleagues emphasize the need for further research to determine whether the observed carbon leakage is a localized phenomenon or a broader trend. “We are now faced with a 30-million-tonne question: we need to determine if Here’s just a small, natural leakage of ancient carbon, or the onset of broadscale destabilization,” Drake explained.

Looking Ahead: Further Research and Monitoring

The research team is now focusing on analyzing water trapped within the Congo Basin’s peat to better understand how microbes are releasing the ancient carbon. They aim to confirm whether this process is occurring across the entire Cuvette Centrale and to quantify oxidation rates to assess the extent of the carbon leakage. This will involve continued field work, laboratory analysis, and modeling to predict future carbon emissions from the region.

Understanding the dynamics of carbon storage and release in the Congo Basin is crucial for global climate mitigation efforts. The region’s vast peatlands represent a significant carbon reservoir, and any changes to their stability could have far-reaching consequences. Continued monitoring and research are essential to inform conservation strategies and to accurately assess the impact of climate change on this vital ecosystem. The findings underscore the interconnectedness of global ecosystems and the urgent need for comprehensive climate action.

For more information on peatlands and carbon cycling, resources are available from the U.S. Environmental Protection Agency and the International Union for Conservation of Nature.