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The article by Winnick and others titled “Weathering intensity and lithium isotopes: A reactive transport perspective” (p. 647–682) incorporates lithium isotope fractionation into weathering models of upland soils to understand the drivers of lithium isotope signals in rivers across the globe. When run over a broad range of water infiltration and erosion rates, the model reproduces global parabolic patterns of dissolved δ⁷Li values as a function of weathering intensity, or the balance of chemical versus physical weathering. However, they find that reduced water travel times under rapid erosion, previously hypothesized to drive global lithium patterns, are inconsistent with observations of high lithium concentrations. Instead, they suggest that lithium concentrations and isotopic composition under rapid erosion are controlled by the supply of lithium-rich, highly weatherable minerals, or alternatively, increased contributions from geothermal waters.

Explanation of cover figure: This figure provides a conceptual model for links between weathering regimes and lithium isotope dynamics based on Bouchez and others (2013) and this study. When weathering is fast relative to erosion, clay dissolution results in low lithium concentrations and dissolved δ⁷Li values. As erosion rates increase, weathering results in clay formation which strongly fractionates lithium isotopes and increases dissolved δ⁷Li. When erosion dominates denudation, reduced soil residence times and the supply of lithium-rich weatherable minerals results in low dissolved δ⁷Li values and high lithium concentrations, in contrast to reduced water transit times as previously hypothesized.