Deciphering the Effect of Vegetation and Erosion on basalt and carbonate weathering by Novel Denudation Rate Approaches

Introduction

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.

Importance of Basalt and Carbonate Rocks

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.

Need for Accurate Descriptions

To formulate sensitivities and feedbacks between the 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.

Factors Influencing Weathering

Besides water flow, erosion rate, and vegetation are thought to exercise significant control. Currently, however, we lack the tools needed to decipher these controls.

Limitations of Current Methods

The preferred approach used to quantify erosion and weathering rates – cosmogenic nuclides, produced in situ in quartz – does not work in basalt and carbonate lithologies.

Project Aim: DEVENDRA

The aim of DEVENDRA, dedicated to the pioneer of cosmogenic nuclide geochemistry Devendra Lal (1920 – 2012), is to eliminate this blind spot using a novel method never applied to basalt and carbonate lithologies: the ratio of cosmogenic beryllium-10 rained out from the atmosphere to stable beryllium-9 released by weathering.

Method Development

DEVENDRA will develop this system as a novel erosion and weathering rate meter for these rocks.

Calibration of Weathering Laws

The project will 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.

Expected Outcomes

The outcomes from DEVENDRA will refine the global weathering models that are used to understand Earth’s carbon cycle on geological time scales. This will help to:

1. Predict the trajectory of anthropogenic CO2 in coming centuries.
2. Estimate the potential for negative CO2 emissions by artificially-enhanced weathering of basalts.