New thermal analysis shows earthquakes and storms reshape Earth’s carbon cycle

A new study shows that ramped pyrolysis/oxidation (RPO) can pinpoint where river-borne carbon comes from after extreme events such as earthquakes and intense storms. By separating organic matter based on how it oxidizes during controlled heating, the method turns a complex sediment mixture into a set of thermally distinct “fingerprints” that reflect carbon source and reactivity.

Earthquakes and rainstorms can trigger widespread landslides and rapidly move large quantities of eroded material downstream. That sediment transport matters for climate: biospheric organic carbon is generally more reactive and breaks down more easily, while its burial in lake and ocean sediments can lock carbon away for thousands of years. Petrogenic organic carbon, derived from ancient sedimentary rocks, can release carbon dioxide when exposed and oxidized during fluvial transport, effectively acting as a geological carbon source.

Until now, identifying which carbon pool dominates in suspended river sediments has been difficult because common tracers—such as stable isotopes, radiocarbon, or molecular biomarkers—can overlap across different materials. The new approach overcomes this ambiguity by progressively heating samples while continuously tracking the CO₂ released at each temperature step.

Researchers built an RPO setup and analyzed suspended sediment collected before and after the 2008 Wenchuan earthquake. They then compared those signals with sediments sampled during a major rainstorm more than a decade later in the upper Minjiang River catchment, an area reshaped by tens of thousands of landslides.

The results reveal contrasting mobilization pathways. More than ten years after the earthquake, as vegetation recovered, the fraction of biospheric organic carbon in transported particulate organic carbon declined at similar suspended sediment concentrations. Meanwhile, thermally stable, rock-derived carbon persisted because loose debris from earthquake-triggered failures continued to supply hillslopes and rivers.

In contrast, the extreme rainstorm mainly mobilized organic carbon associated with surface soils and vegetation. These sources are typically more chemically reactive and more tightly linked to the modern carbon cycle, producing a different thermal response than rock-derived material.

Crucially, RPO can distinguish these sources within a single river sample, offering an independent line of evidence from thermal stability rather than relying solely on chemical or isotopic proxies. This capability helps clarify how event type controls the evolution of carbon export during transport.

With climate change expected to intensify mountain rainfall extremes and tectonic regions continuing to experience large earthquakes, accurately tracking carbon mobilization will be increasingly important for carbon-cycle models and future climate feedback predictions.

The authors report the work in Science China Earth Sciences, demonstrating that RPO provides a powerful new tool for tracing how landscapes reshape the carbon carried by rivers long after the initial disturbance.