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Biological and geological carbon cycles are closely linked, according to a study published in Nature. Results from investigations in rivers on the Qinghai–Tibet Plateau challenge the simplified view of thawing permafrost as solely a carbon source.

ImageLiwei Zhang

Thawing permafrost is often viewed as a growing source of greenhouse gases as climate warming releases ancient carbon stored in frozen soils. But a new study published in the journal Nature reveals a more complex picture. As permafrost thaws, rivers may also develop an overlooked capacity to remove carbon dioxide (COâ‚‚) through intensified rock weathering. Researchers found that warming and permafrost degradation expose reactive minerals and increase water–rock interactions, accelerating chemical weathering processes that consume COâ‚‚. In some river catchments, this geological carbon uptake partially or even fully offset river COâ‚‚ emissions.

The international research team investigated 50 rivers across the Qinghai–Tibet Plateau, Earth’s largest high-altitude cryosphere outside the polar regions, to understand how thawing permafrost reshapes carbon cycling. By combining measurements of river COâ‚‚ emissions, dissolved carbon, isotopic tracers and geochemical modelling, the researchers found evidence that thawing landscapes intensify chemical weathering, transferring carbon into dissolved inorganic forms while consuming atmospheric COâ‚‚.

Carbon uptake can even exceed emissions

“We found that river COâ‚‚ emissions decline while carbon uptake through rock weathering increases as permafrost cover decreases,” said Liwei Zhang, biogeochemist at East China Normal University. “In some catchments where permafrost has become patchier, weathering-driven carbon uptake was large enough to offset or even exceed river COâ‚‚ emissions.”

Our findings show that biological and geological carbon cycles are tightly linked

Across the study region, the team estimated that carbon uptake from rock weathering offsets roughly 35 percent of river COâ‚‚ emissions on average. In regions with continuous permafrost, the offset was relatively small. However, in landscapes with discontinuous or isolated permafrost, weathering-driven carbon uptake sometimes exceeded 100 percent of river COâ‚‚ emissions, suggesting that geological carbon uptake can rival biological carbon release.

Biological and geological carbon cycles linked

The findings challenge a simplified view of thawing permafrost as only a carbon source. As frozen soils thaw, rivers receive large inputs of ancient organic carbon that microbes convert into greenhouse gases released to the atmosphere. The new study suggests that geological processes operating alongside biological ones may partly counterbalance these emissions.

Still, the researchers caution that rock weathering is not a simple or permanent climate solution. Carbon cycling in thawing landscapes remains complex, and some weathering reactions can also release COâ‚‚ depending on mineral composition. The study instead highlights a mechanism that remains poorly represented in many climate and carbon-cycle models.

Jan Karlsson.

ImageMattias Pettersson

“Our findings show that biological and geological carbon cycles are tightly linked,” says Jan Karlsson, professor at Department of Ecology, Environment and Geosciences at Umeå University. “To understand whether thawing permafrost ultimately amplifies or dampens climate warming, we need to consider both the carbon released from ancient soils and the carbon consumed through rock weathering.”

The researchers argue that future climate assessments should move beyond a sole focus on biological driven carbon emissions and incorporate geological carbon sources and sinks that emerge as frozen landscapes thaw.