The lithium isotope response to the variable weathering of soils in Iceland

Philip A.E. Pogge von Strandmann*, Kevin W. Burton, Sophie Opfergelt, Bianca Genson, Rannveig A. Guicharnaud, Sigurður R. Gislason

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

This study has analysed Li isotopes ratios from well-studied soil and pore water profiles from Iceland that have the same parent material but have experienced different degrees of chemical weathering. Thus, from least to most weathered, we have analysed vitrosols (V), gleyic andosols (GA), brown andosols (BA), Histosols (H) and Histic Andosols (HA). Although the most weathered H and HA soils have the highest content in clay-sized material, they have the least fractionated δ7Lipore water values. In contrast, the least weathered GA and BA pore waters are most fractionated for Li isotopes. Given that Li isotope ratios are fractionated by clay mineral formation, this appears counter-intuitive. A single trend for all samples of δ7Li as a function of Li/Na ratios suggests that they are all controlled by a process with a single fractionation factor, in this case likely the formation of poorly-crystalline allophane, which dominates in the “least weathered” soils. This rapidly forming secondary mineral dominates Li isotope fractionation over more slowly-forming crystalline clays. The fractionation along a single path shows that the key process here in controlling the Li isotope ratio of surface waters is the degree of Li uptake by secondary minerals. This does not necessarily correspond to the amount of clay minerals present in the soil, but to the amount of clay minerals that are being newly formed in a single passage of the pore water through the soil, or are in equilibrium with soil solutions at the time of sampling.

Original languageEnglish
Pages (from-to)55-73
Number of pages19
JournalGeochimica et Cosmochimica Acta
Volume313
DOIs
Publication statusPublished - 1 Aug 2021

Bibliographical note

Funding Information:
This study and PPvS were funded by ERC Consolidator grant 682760 CONTROLPASTCO2. Birkbeck, University of London is thanked for the undergraduate project of BG. We would like to thank Kristján Jónasson and the Icelandic Institute of Natural History for providing the secondary mineral samples.

Funding Information:
This study and PPvS were funded by ERC Consolidator grant 682760 CONTROLPASTCO2. Birkbeck, University of London is thanked for the undergraduate project of BG. We would like to thank Kristj?n J?nasson and the Icelandic Institute of Natural History for providing the secondary mineral samples.

Publisher Copyright:
© 2021 Elsevier Ltd

Other keywords

  • Degree of weathering
  • Pore waters
  • Secondary minerals
  • Silicate weathering
  • Soil weathering

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