Trace element and kinetic data from competitive ligand exchange experiments on water and soils from eight Aotearoa-New Zealand caves

This dataset provides all data discussed and presented in the manuscript "Characterising the decay of organic metal complexes in speleothem-forming cave waters" by Sebastian N. Höpker, Sebastian F. M. Breitenbach, Megan Grainger, Claudine H. Stirling, and Adam Hartland.

The dataset is the basis for the kinetic characterisation of organic metal complex (OMC) dissociation rates in water samples (drips and cave streams) and soil extracts (1:10 weight:volume CaCl2 extraction) from eight cave systems in Aotearoa-New Zealand. The study aimed to explore the magnitude and variability of OMC stability in various karst systems to assess the role of OMC decay in determining speleothem (cave carbonate) trace metal concentrations. Kinetic experiments were conducted using competitive ligand exchange (CLE) with Chelex-100 resin as competing ligand. Cave water samples were spiked with 5 ppb of Co, Ni, Cu prior to analysis. Experiments were carried out at solution pH 8.5 and ca. 22 °C. Upon addition of Chelex-100, 11 aliquots were taken over the course of 2 hours via a syringe, and immediately filtered using 0.45 micron filters. Quantification of metal concentrations as reported here was carried out by inductively-coupled plasma mass spectrometry (ICP-MS). Most experiments clearly depict an exponential decrease in metal concentrations in the test solutions over time, reflecting the dissociation of OMCs present in the solution. The data were used to fit kinetic models and derive dissociation rate constants discussed in the manuscript. The dataset further includes all manuscript tables and supplementary tables, as well as data used in a simple forward model presented in the manuscript. Data are provided in individual tabs. A brief description of each tab and variable is provided in the tab "README".

Our experiments 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 NOM 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-1, corresponding to ca. <5.6 mL min-1), and therefore provides a general, mechanistic link to a quantitative proxy of palaeoclimatic cave drip rates.

本数据集涵盖了Sebastian N. Höpker、Sebastian F. M. Breitenbach、Megan Grainger、Claudine H. Stirling以及Adam Hartland所撰写的论文"Characterising the decay of organic metal complexes in speleothem-forming cave waters"中讨论和展示的全部数据。

本数据集是针对新西兰奥特亚罗瓦（Aotearoa-New Zealand）8个洞穴系统的水样（洞穴滴水与洞穴溪流）及土壤提取物（按1:10重量体积比的氯化钙（CaCl2）萃取液）中有机金属络合物（organic metal complex, OMC）解离速率进行动力学表征的核心依据。本研究旨在探索各类喀斯特系统（karst system）中OMC稳定性的幅度与变异性，以评估OMC降解在决定石笋（speleothem，洞穴碳酸盐沉积）痕量金属浓度中的作用。

动力学实验采用竞争性配体交换（competitive ligand exchange, CLE）方法，以Chelex-100树脂作为竞争性配体。分析前，洞穴水样被添加5 ppb的钴（Co）、镍（Ni）、铜（Cu）。实验在溶液pH为8.5、温度约22℃的条件下开展。加入Chelex-100树脂后，在2小时内通过注射器采集11份等分试样，并立即使用0.45微米滤膜过滤。如本文所述，金属浓度的定量分析采用电感耦合等离子体质谱法（inductively-coupled plasma mass spectrometry, ICP-MS）完成。

多数实验清晰显示，测试溶液中的金属浓度随时间呈指数级下降，反映了溶液中存在的OMC发生了解离。本数据集被用于拟合动力学模型，并推导论文中讨论的解离速率常数。此外，本数据集还包含论文中的全部表格与补充表格，以及论文中展示的简单正向模型（forward model）所用的数据。所有数据以独立工作表（tab）形式提供，每个工作表及变量的简要说明收录于名为"README"的工作表中。

本实验证实，天然有机质（natural organic matter, NOM）配体限制了滴水-石笋界面处过渡金属（transition metal）的可利用性，其稳定性顺序大致为Cu ≈ Co > Ni；而碱土金属（alkaline earth metal）镁（Mg）与锶（Sr）几乎不存在有机络合现象。在各类水样中未观测到OMC稳定性随NOM特征发生系统性变化，但在有机质含量相对较高的土壤提取物中，络合作用显著增强。

研究结果表明，向石笋供应的过渡金属含量与滴水速率呈负相关关系：通过OMC的降解，过渡金属供应量随滴水间隔的延长而增加。该过程在典型石笋形成环境相关的时间尺度上（约<0至40滴每分钟，对应约<5.6毫升每分钟）最为敏感，因此为古气候洞穴滴水速率的定量代用指标（proxy）提供了普适性的机制性关联。