Control of temperature on the weathering of slow-eroding post-orogenic terrains

The long-term climate stability of the Earth has been attributed to the negative feedback between the rate of CO₂-consuming silicate weathering and the partial pressure of atmospheric CO₂. It is generally believed that the capability of silicate weathering in feedbacking climate is mainly associated with the rapid-eroding mountains where fresh bedrock adequately exposes. In contrast, the slow-eroding terrains are considered to have low climate sensitivity of silicate weathering due to the almost complete depletion of CO₂-consuming Ca and Mg cations in highly-weathered top regolith. However, much of the Earth's history, marked by tectonic quiescence and slow erosion, has also exhibited significant climate stability. Here we demonstrate that the slow-eroding post-orogenic terrains exceptionally show strong temperature dependence of silicate weathering. This conclusion is drawn from a historical reconstruction of the weathering-derived clay production over the past ∼23 million years, based on the sediments from the Ocean Drilling Program sites 1147/1148 offshore from the South China continent. We employ a sensitive proxy, the Rb/Zr ratio of fine sediments, showing that weathering of exposed granitic plutons closely tracks temperature changes. The resulting apparent activation energy (Ea) of silicate weathering (77.1 ± 14.9 kJ/mol) is significantly higher than previous estimations for the slow-eroding terrains. Given the temporal and spatial dominance of slow-eroding terrains on global weathering flux, our findings suggest that the strong temperature dependence of weathering in these settings would largely enhance the sensitivity of global silicate weathering flux in response to temperature changes. This may help to explain the Earth's climate stability, particularly during periods of tectonic quiescence.