Periodic Reporting for period 1 - DEVENDRA (Deciphering the Effect of Vegetation and Erosion on basalt and carbonate weathering by Novel Denudation Rate Approaches)
Période du rapport: 2023-04-01 au 2025-09-30
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.
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.
The work consists of three independent approaches.
1) A central innovation within DEVENDRA is the development and implementation of the 10Be(meteoric)/9Be isotope system as a robust method for determining denudation rates in quartz-free lithologies, such as carbonate and mafic rocks. This work entails meticulous chemical work in dedicated ultra-clean laboratories, and Accelerator Mass Spectrometry to measure virtually single atoms of 10Be (perforemd at Universität zu Köln).
2) Intense field work of the enrire DEVENDRA team at several locations worldwide that differ in climate:
a. Temperate climate: Central Germany (Vogelsberg vocanic province and Swabian Alps limestones)
b. Mediterranean climate: Sardinia, Italy
c. Tropical humid climate: Eastern and Western Cordillera in Colombia
d. Subartic climate: West Canada (Rocky Mountains, Vancouver Island)
3) Employing a combination of water flow measurements in streams, water elemental chemical concentrations, and reactive flow models to derive the laws of weathering, namely the “reactivity” of these rocks (their capacity to resist the impact of weather). In addition we establish full inorganic elemental budgets of the ecosystems that cover our sampling sites. These provide the impact of plants on rock weathering.
1) A central innovation within DEVENDRA is the development and implementation of the 10Be(meteoric)/9Be isotope system as a robust method for determining denudation rates in quartz-free lithologies, such as carbonate and mafic rocks. This work entails meticulous chemical work in dedicated ultra-clean laboratories, and Accelerator Mass Spectrometry to measure virtually single atoms of 10Be (perforemd at Universität zu Köln).
2) Intense field work of the enrire DEVENDRA team at several locations worldwide that differ in climate:
a. Temperate climate: Central Germany (Vogelsberg vocanic province and Swabian Alps limestones)
b. Mediterranean climate: Sardinia, Italy
c. Tropical humid climate: Eastern and Western Cordillera in Colombia
d. Subartic climate: West Canada (Rocky Mountains, Vancouver Island)
3) Employing a combination of water flow measurements in streams, water elemental chemical concentrations, and reactive flow models to derive the laws of weathering, namely the “reactivity” of these rocks (their capacity to resist the impact of weather). In addition we establish full inorganic elemental budgets of the ecosystems that cover our sampling sites. These provide the impact of plants on rock weathering.
Enhanced basalt weathering may help dictate the trajectory of Earth’s climate in the Anthropocene by being a key part of negative emission strategies. Estimates suggest that up to 0.5-2 Gt/y CO2 can be sequestered by the distribution of 1-5 Gt/y of powdered basalt onto soils. DEVENDRA’s 10Be(meteoric)/9Be approach might provide means to predict the efficiency of this method in natural environments.