Organic metal complexes (OMCs) transport trace metals (, Co, Ni, Cu) from surface soils, via the unsaturated zone, to sites of cave carbonate (speleothem) formation. OMCs clearly imprint on speleothem trace element chemistry, but the role of kinetic factors in the signal transfer process has yet to be elucidated. We investigated whether OMCs may viably link metal concentrations in stalagmites and local hydrology (, drip rate), via their time-sensitive dissociation (or ‘decay’) in the speleothem water thin-film. We performed competitive ligand exchange experiments using water and soil samples from eight geographically diverse Aotearoa New Zealand caves, providing a first comparative characterisation of speleothem-specific OMC kinetics. Critically, this approach corroborated that NOM ligands limit transition metal availability at the dripwater-speleothem interface, exhibiting stabilities on the order Cu ≈ Co > Ni, whereas organic complexation of the alkaline earth metals Mg and Sr was virtually absent. Systematic variations of OMC stability with natural organic matter characteristics were not observed amongst water samples, whilst enhanced complexation was clearly evident in the comparably organic-rich soil extracts. Our results imply that the supply of transition metals to speleothems is inversely related to drip rate, increasing with drip interval via the decay of OMCs. This process appears most sensitive on time-scales relevant to typical speleothem-forming settings (<0 to ca. 40 drips min, corresponding to ca. <5.6 mL min), and therefore provides a general, mechanistic link to a quantitative proxy of palaeoclimatic cave drip rates.

中文翻译：

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表征形成洞穴水域的有机金属配合物的衰变

有机金属配合物 (OMC) 将痕量金属（Co、Ni、Cu）从表层土壤通过非饱和带输送到洞穴碳酸盐（洞穴）形成的地点。 OMC 清楚地影响了洞穴微量元素化学，但动力学因素在信号传递过程中的作用尚未阐明。我们研究了 OMC 是否可以通过其在洞穴水薄膜中的时间敏感解离（或“衰变”），将石笋中的金属浓度与当地水文（滴水率）有效联系起来。我们使用来自新西兰八个不同地理洞穴的水和土壤样本进行了竞争性配体交换实验，首次提供了洞穴植物特异性 OMC 动力学的比较表征。重要的是，这种方法证实了 NOM 配体限制了滴水-洞穴界面处过渡金属的可用性，表现出 Cu ≈ Co > Ni 顺序的稳定性，而碱土金属 Mg 和 Sr 的有机络合几乎不存在。在水样中没有观察到 OMC 稳定性随天然有机质特征的系统变化，而在相对富含有机物的土壤提取物中，络合作用明显增强。我们的结果表明，过渡金属对洞穴的供应与滴水率成反比，通过 OMC 的衰变，随着滴水间隔的增加而增加。该过程在与典型洞穴形成环境相关的时间尺度上显得最敏感（<0 至约 40 滴/分钟，对应于约<5.6 mL/分钟），因此为古气候的定量代理提供了一般的机械联系洞穴滴水率。