The erosion of active mountain ranges exposes rocks to the surface of the Earth. Acidic rain- and soil waters slowly dissolve minerals in these rocks. Depending on the type of mineral, these “chemical weathering” reactions can either draw down CO₂ from the atmosphere or release CO₂. Therefore, uplift of different rock-types in mountain ranges can potentially affect Earth’s climate.

In our recent study, we wanted to investigate how rock-type affects the balance of CO2 drawdown and release in mountains. We collected waters from small streams on the eastern Tibetan Plateau. These streams drain regions with either metasedimentary or granitoid rocks. Moreover, the erosion rates of the mountains vary by more than two orders of magnitude. This contrast can be clearly seen in the shape of the landscape.

Across the erosion rate gradient, we find that granitoid lithologies have generally lower weathering rates than metasedimentary rocks. Using a mixing model, we can infer the carbon balance of these weathering reactions. For all lithologies, increasing erosion shifts weathering from CO2 drawdown to CO2 release. This shift is most dramatic for metasedimentary rocks.

Throughout the history of a mountain belt, different rock-types are exposed to the surface of the Earth. Our results suggest that changes in the exposure of rocks can alter the carbon cycle and earth’s climate in addition to changes in erosion rates.

Bufe, A., Cook, K.L., Galy, A., Wittmann, H., Hovius, N. (2022). The effect of lithology on the relationship between denudation rate and chemical weathering pathways. Evidence from the eastern Tibetan Plateau. Earth Surface Dynamics. 10(3), 513-530. Journal Link