Shafaq News/ A new study revealed that rivers release significant amounts of ancient carbon dioxide (CO₂) into the atmosphere, challenging previous assumptions about the carbon cycle.

The research, published as the cover story of Nature and led by scientists at the University of Bristol, shows that over half of the carbon gases released from rivers originate from long-term carbon stores, such as deep soil layers and weathered rock. This contrasts with prior beliefs that river emissions stemmed mostly from recent organic material.

According to the study, about 60% of river-based CO₂ and methane emissions are sourced from ancient reservoirs of carbon—some dating back thousands or even millions of years—while the remaining 40% is from recent organic decomposition.

The findings emerged from carbon isotope analysis conducted on over 700 river sites across 26 countries. By comparing levels of carbon-14 in river gases to those in modern atmospheric CO₂, the scientists were able to determine the relative age of the emissions.

Dr. Josh Dean, Associate Professor in Biogeochemistry at the University of Bristol and lead author of the study, explained that “old carbon stores are leaking out much more into the atmosphere than previous estimates suggested,” describing the findings as “surprising and potentially huge” in terms of their global implications.

The study estimates that rivers globally emit approximately two gigatons of carbon annually—roughly one-fifth of emissions produced by human activity. Co-author Dr. Gemma Coxon from the University of Bristol stressed the need to re-evaluate these crucial parts of the global carbon cycle, adding that the implication is that plants and soils are likely absorbing about one gigatons more CO₂ per year than previously estimated to compensate for this unrecognized source.

The research team plans to further investigate the variability in carbon age across different rivers and assess how this trend may have shifted over time.