Pogge Von Strandmann, P;
Fraser, W;
Hammond, S;
Tarbuck, G;
Wood, I;
Oelkers, E;
Murphy, M;
(2019)
Experimental determination of Li isotope behaviour during basalt weathering.
Chemical Geology
, 517
pp. 34-43.
10.1016/j.chemgeo.2019.04.020.
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Abstract
Silicate weathering is the primary control of atmospheric CO2 concentrations on multiple timescales. However, tracing this process has proven difficult. Lithium isotopes are a promising tracer of silicate weathering. This study has reacted basalt sand with natural river water for ~9 months in closed experiments, in order to examine the behaviour of Li isotopes during weathering. Aqueous Li concentrations decrease by a factor of ~10 with time, and δ7Li increases by ~19‰, implying that Li is being taken up into secondary phases that prefer 6Li. Mass balance using various selective leaches of the exchangeable and secondary mineral fractions suggest that ~12–16% of Li is adsorbed, and the remainder is removed into neoformed secondary minerals. The exchangeable fractionation factors have a Δ7Liexch-soln = −11.6 to −11.9‰, while the secondary minerals impose Δ7Lisecmin-soln = −22.5 to −23.9‰. Overall the experiment can be modelled with a Rayleigh fractionation factor of α = 0.991, similar to that found for natural basaltic rivers. The mobility of Li relative to the carbon-cycle-critical cations of Ca and Mg changes with time, but rapidly evolves within one month to remarkably similar mobilities amongst these three elements. This evolution shows a linear relationship with δ7Li (largely due to a co-variation between aqueous [Li] and δ7Li), suggesting that Li isotopes have the potential to be used as a tracer of Ca and Mg mobility during basaltic weathering, and ultimately CO2 drawdown.
| Type: | Article |
|---|---|
| Title: | Experimental determination of Li isotope behaviour during basalt weathering |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1016/j.chemgeo.2019.04.020 |
| Publisher version: | https://doi.org/10.1016/j.chemgeo.2019.04.020 |
| Language: | English |
| Additional information: | This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | Chemical weathering, Weathering experiments, Isotope fractionation, Basalt 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-pp.ucl.ac.uk/id/eprint/10072996 |
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