Pogge von Strandmann, Philip AE;
He, Xiaoqing;
Zhou, Ying;
Wilson, David J;
(2025)
Comparing open versus closed system weathering experiments using lithium isotopes.
Applied Geochemistry
, Article 106458. 10.1016/j.apgeochem.2025.106458.
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Abstract
Chemical weathering of silicate rocks represents a critical part of the carbon cycle, and also a potential method for the artificial drawdown of atmospheric CO2 (“enhanced weathering”). However, weathering and particularly the resulting secondary minerals (especially clays) have proven hard to measure and quantify. Here we use lithium isotopes to examine and compare two different types of laboratory weathering experiments, using the same initial water and rock, in order to determine their similarities and differences. Specifically, we compare “open system” experiments, where the reacting water drips through the rock powder, with “closed system” experiments, where the reacting water and rock are in contact in a closed beaker. The results (elemental ratios, mobility calculations, saturation indices) suggest that closed experiments, with their longer water-rock interactions times, exhibit more secondary minerals formation. This finding is confirmed by their higher “equilibrium” solution δ7Li values (δ7Li = 35.7 versus 29.5 ‰, respectively). The determination of their observed fractionation factors (α = 0.983 ± 0.004 and 0.977 ± 0.003 for the open and closed experiments, respectively) and partition coefficients between water and secondary minerals yields a test case, to determine whether the amount of clays that form during weathering can be calculated solely from Li isotope ratios, giving values similar to the amount of basalt dissolved. Based on potassium concentration (here the most mobile element), 1.9–3.2 g of rock was dissolved. Based on the Li isotopes, 1.6–2.0 g of clay was precipitated during the month-long experiment. This result agrees with other estimates from isotope systems, which suggest that clay formation is rapid, which in turn has consequences for weathering processes, and especially for the efficiency of enhanced weathering.
| Type: | Article |
|---|---|
| Title: | Comparing open versus closed system weathering experiments using lithium isotopes |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1016/j.apgeochem.2025.106458 |
| Publisher version: | https://doi.org/10.1016/j.apgeochem.2025.106458 |
| Language: | English |
| Additional information: | © 2025 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). |
| Keywords: | Weathering, Li isotope fractionation, Experiments, Enhanced weathering |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10209007 |
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