Periodic Reporting for period 1 - SIFFT (Solute Isotope Fractionation during Fluid Transit)
Reporting period: 2021-02-01 to 2023-01-31
The chemical dissolution (or weathering) of continental silicate rocks is a crucial Earth System process that makes nutrients available to ecosystems and consumes atmospheric CO2, affecting climate and habitability on Earth over geological timescales. Understanding the mechanistic controls on chemical weathering is one of the big challenges in Earth Science. Predicting how nutrient and carbon cycles, driven by weathering, will respond to the anthropogenic perturbation of atmospheric composition, the hydrological cycle, and natural ecosystems is a major European and global environmental research priority. The SIFFT project uses a combination of geochemical and hydrological techniques, coupled with laboratory experiments, to investigate the mechanistic relationship between hydrology and weathering. The overall objective is to test whether certain geochemical tracers (such as silicon stable isotope ratios) can be used to reconstruct how the speed of weathering reactions is controlled by water flow through soils and rocks.
To achieve the aims of this project, two fieldtrips to the Capesterre river catchment in Guadeloupe were made, along with monthly sampling trips by local collaborators. In total, several hundred samples of river water, rain water, soil water, rocks, and vegetation were collected and characterized physically and chemically using different techniques, with a total of over a thousand different analyses. In addition, several batch weathering experiments were carried out, with experimental runtime of 300 days. The results have revealed large variations in the chemical composition of river water during storm events, demonstrating the major role of hydrology on weathering, confirming the role of hydrology outlined in one of the proposed hypotheses.
In the SIFFT project, we have amassed the single largest dataset of silicon isotope ratios to date at any given site. In addition, silicon isotope dynamics in a natural watershed were for the first time investigated in combination with controlled lab experiments, allowing to directly constrain key parameters required to model and interpret they system. Final (ongoing) part of the project combines all the obtained data in a new model framework in order to unequivocally test two competing hypotheses on the hydrological control of weathering. Overall, this work is expected to advance our understanding of chemical weathering dynamics, with implications for constraining global carbon budgets in the context of geologic and anthropogenic climate change, and to influence the design of carbon capture solutions based around enhanced weathering of silicate rocks.