Quaternary denudation rates in a tropical volcanic island: example of Santo Antao in Cabo Verde

The Earth surface, where life develops and stands, is strongly affected by denudation which is the sum of physical erosion and chemical weathering. Denudation impacts soil formation and agriculture, affects the relief stability and, at the geological time scale, controls the atmospheric CO₂ via the weathering of silicates and the production of sediments that later bury organic matter in the oceans. In the context of global warming, it is particularly important to predict how denudation will change and hence impact the Earth Surface where we live. This requires to understand the links between past climate variability and denudation changes, especially during the Quaternary when Earth experienced rapid climate oscillations of amplitude similar to what is expected in the future due to anthropic impact. To reach this goal, quantitative estimate of past denudation rates during the Quaternary are needed especially in Volcanic island located in tropics because here silicate weathering and hence CO2 consumption is particularly efficient.

In this study, we reconstruct Quaternary paleo-denudation rates in Santoa Antao, one of the largest islands of the Cabo Verde archipelago that is located in the Atlantic ocean 800 km off the coast of Senegal. To reconstruct the paleo-denudation rates we measured in situ cosmogenic ³He concentrations in ancient fluvial sediments stored in deep entrenched valleys across the island. The depositional ages of sediments were determined by dating using Ar/Ar adjacent volcanic layers (pumices or basalt lavas). For comparison between all data, paleo-denudation rates are normalized to modern ³He derived denudation rates across the same drainage basin obtained from the analysis of modern river sand in a previous study. This yields to a 0-550ka record of paleo-denudation rates that is compared to climate variations to discuss the potential links between the two.