Comparison of the range of lithium isotopic ratios measured in this work at the Bisley 1 catchment in Puerto Rico with those previously published.
Comparison of the range of lithium isotopic ratios (δ7 Li) measured in this work at the Bisley 1 catchment in Puerto Rico (colored, bottom three rows) with those previously published (black, top nine rows). The values reported in this study are remarkable for including the lowest ever reported regolith and porewater values, a range of δ7 Li values spanning 87 per mille, and unexpected relationships between the regolith, porewater, and stream water. Credit: Chapela Lara et al. [2022], Figure 2
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Earth Surface

For non-traditional stable isotopes to become great tracers in terrestrial biogeochemical processes, we need to better understand their fractionation mechanisms. This is challenging in critical zone research due to the complex interaction of air, soil, rock, water, and biota.

Chapela Lara et al. [2022] investigated lithium isotope systematics during chemical breakdown of andesitic volcanic bedrock at the Luquillo Critical Zone Observatory. Located in Puerto Rico and characterized by tropical climate, the soils at the study site are well developed and have experienced extreme weathering, as primary minerals in andesite transform to secondary clays and then oxides.

Co-evolution of lithium concentrations and isotope ratios is examined in the context of such mineralogy shifts. Lithium isotope ratios have changed dramatically: the authors document the lowest values ever documented on Earth, which they attribute to different weathering reactions. The authors find that, against general belief, the isotopic ratio of streamwater does not reflect this extreme weathering.

This comprehensive study contributes greatly to the science community and develops further a robust tool to better understand the evolution, service, and functions of critical zones.

Citation: Chapela Lara, M., Buss, H. L., Henehan, M. J., Schuessler, J. A., & McDowell, W. H. (2022). Secondary minerals drive extreme lithium isotope fractionation during tropical weathering. Journal of Geophysical Research: Earth Surface, 127, e2021JF006366.

—Lixin Jin, Associate Editor, Journal of Geophysical Research: Earth Surface

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