Permafrost thaw releases CO2, but rocks can absorb some of it
Climate warming is melting permafrost, releasing immense amounts of organic carbon trapped for millennia. Once mineralized, this carbon is emitted as carbon dioxide into the atmosphere by rivers, thereby amplifying the greenhouse effect. However, this is not the only dynamic at play. Thawing also exposes minerals previously protected, accelerating their chemical weathering. This process, known as rock weathering, can capture carbon dioxide by producing ions that neutralize acidity or form carbonates.
A study conducted on the Tibetan Plateau, where permafrost is particularly vulnerable, reveals a complex interaction between these two mechanisms. Researchers observed that in areas with continuous permafrost, CO2 emissions from rivers dominate. In contrast, where permafrost becomes discontinuous or isolated, rock weathering takes over. In these cases, the CO2 absorbed by mineral weathering can exceed river emissions, sometimes even fully offsetting them.
The Tibetan Plateau, with its 780,000 square kilometers of watersheds, provides an ideal setting to study these phenomena. Rivers there transport ancient organic carbon from thawing permafrost, as well as inorganic carbon from rock weathering. Analyses show that one-third of the dissolved organic carbon in these rivers comes from ancient sources, such as permafrost or rocks, while the rest is more recent. Inorganic carbon, on the other hand, partly comes from the weathering of carbonates and silicates—minerals that, when dissolved, trap CO2.
The results indicate that, in some areas, rock weathering absorbs up to 35% of river CO2 emissions. In regions where permafrost is less extensive, this percentage can even exceed 100%, meaning absorption surpasses emissions. This phenomenon could intensify with warming, as thawing exposes more reactive mineral surfaces.
Rock weathering acts as a natural counterbalance to carbon emissions. While sulfides, such as pyrite, release CO2 when oxidized, the weathering of carbonates and silicates absorbs it. On the Tibetan Plateau, where carbonates dominate, this process mitigates some of the emissions linked to thawing. However, in sulfide-rich areas, the oxidation of these minerals could worsen CO2 releases.
Rivers on the Tibetan Plateau currently emit about 2.3 million tons of carbon per year as CO2. At the same time, rock weathering absorbs approximately 0.8 million tons, or 35% of fluvial emissions. These figures show that, even as permafrost thaw releases ancient carbon, geochemical reactions can neutralize a significant portion of it.
This discovery highlights the importance of considering both biological and geological processes to understand the impact of thawing on the carbon cycle. Climate models should incorporate these mechanisms to accurately assess the role of permafrost regions in global warming.
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Cited Study
DOI: https://doi.org/10.1038/s41586-026-10664-8
Title: Rock weathering can counteract river CO2 emissions induced by permafrost thaw
Journal: Nature
Publisher: Springer Science and Business Media LLC
Authors: Liwei Zhang; Aaron Bufe; Joshua F. Dean; Gerard Rocher-Ros; Ryan A. Sponseller; Emily H. Stanley; Jan Karlsson; David E. Butman; Ran Liu; Lijun Hou; Jinzhi Ding; Shilong Piao; Xinghui Xia; Tom J. Battin