The chemical weathering of rocks on the Earth’s surface draws down atmospheric CO2, balancing emissions from volcanoes and maintaining habitable temperatures. Basalt and carbonate rocks are particularly crucial in this balance, because they are efficiently weathered: as estimated from studies of the dissolved elements in rivers, basalt accounts for 20-35% of modern global silicate weathering and CO2 consumption flux, despite only covering 5% of Earth’s surface. To formulate sensitivities and feedbacks between weathering of these rocks and climate, we need an accurate description of the exact processes that drive the conversion of rock to soil by weathering. Besides water flow, erosion rate and vegetation are thought to exercise significant control.
The aim of DEVENDRA, dedicated to the pioneer of cosmogenic nuclide geochemistry Devendra Lal (1920 – 2012), is to make basalt and carbonate rocks accessible to determining the rates at which these rocks get weathered and eroded. We employ a novel method never applied to basalt and carbonate lithologies: the ratio of the rare cosmogenic isotope beryllium-10 produced by cosmic rays rained out from the atmosphere that of stable beryllium-9 released by weathering. In DEVENDRA we develop this system, and use this new method to calibrate – using globally-distributed soil profiles and catchments of differing climate and erosion rate – the laws that govern weathering and CO2 drawdown in these rocks. The outcomes from DEVENDRA will refine the global weathering models that are used to understand Earth’s carbon cycle on geological time scales, to predict the trajectory of anthropogenic CO2 in coming centuries, and to estimate the potential for negative CO2 emissions by artificially-enhanced weathering of basalts.
