Lithium (Li) isotopes are a tracer of silicate weathering processes, but how they react to different components of organic and plant-assisted weathering is poorly known. To examine the effect of organic acids compared to a strong mineral acid (HCl) on Li isotope behaviour, basalt-water weathering experiments were amended with different organic acids (glycine, malic acid, cinnamic acid, and humic acid; 0.01 M). The presence of the different acids significantly affects the behaviour of dissolved elemental concentrations (such as Mg, Fe, and Al), both by increasing primary rock dissolution and hindering rates of secondary mineral formation. However, the behaviour of Li isotopes appears unaffected, with all experiments following an almost identical trend of δ⁷Li versus Li/Na. This observation was consistent with a single fractionation factor during the uptake of Li into secondary minerals, yet both calculated saturation states and leaching experiments on the reacted solids indicated that Li was removed into multiple phases, suggesting that the bulk combined fractionation factor barely varied. Of the Li lost from solution in the organic experiments, we estimated that on average 76% went into neoformed clays, 16% into oxides/oxyhydroxides, and 10% into the exchangeable fraction. The fractionations observed for each phase were Δ⁷Li_exch-soln = −12.7 ± 1.7‰, Δ⁷Li_ox-soln = −26.7 ± 0.4‰, and Δ⁷Li_clay-soln = −21.6 ± 3.3‰. These fractionations were identical, within error, to those from experiments with organic-free water, implying that the Li isotope behaviour was unaffected by the presence of organic acids in the weathering reaction. This result has interesting consequences for the interpretation of Li isotopes in terms of plant-assisted weathering and the geological record of terrestrialisation. In particular, it appears to imply that seawater Li isotope records can be expected to resolve the integrated effect of plants on weathering fluxes or weathering congruence, rather than being sensitive to specific organic-mediated weathering mechanisms.

锂 (Li) 同位素是硅酸盐风化过程的示踪剂，但它们如何对有机和植物辅助风化的不同成分作出反应却鲜为人知。为了检查有机酸与强无机酸 (HCl) 相比对 Li 同位素行为的影响，玄武岩水风化实验用不同的有机酸（甘氨酸、苹果酸、肉桂酸和腐殖酸；0.01 M）进行了修正。不同酸的存在显着影响溶解元素浓度（如 Mg、Fe 和 Al）的行为，既增加原生岩石溶解，又阻碍次生矿物形成速率。然而，Li 同位素的行为似乎不受影响，所有实验都遵循几乎相同的 δ ^7趋势Li 对 Li/Na。这一观察结果与锂吸收到次生矿物中的单一分馏因子一致，但计算的饱和状态和反应固体的浸出实验均表明锂被去除为多相，这表明整体组合分馏因子几乎没有变化。在有机实验中从溶液中损失的锂中，我们估计平均 76% 进入新成型粘土，16% 进入氧化物/羟基氧化物，10% 进入可交换部分。每相观察到的分馏为 Δ ⁷ Li _exch-soln  = -12.7 ± 1.7‰、Δ ⁷ Li _ox-soln  = -26.7 ± 0.4‰ 和 Δ ⁷ Liclay _-soln = -21.6 ± 3.3‰。这些分馏与无有机水实验中的分馏完全相同，误差不超过，这意味着 Li 同位素行为不受风化反应中有机酸存在的影响。这一结果对于在植物辅助风化和陆地化地质记录方面解释锂同位素具有有趣的结果。特别是，这似乎意味着海水 Li 同位素记录有望解决植物对风化通量或风化一致性的综合影响，而不是对特定的有机介导的风化机制敏感。