Laboratoire de Physico-Chimie de l'Atmosphère, Université du Littoral Côte d'Opale, 189A Avenue Maurice Schumann, 59140, Dunkerque, France.
Laboratório de Águas e Efluentes & Laboratório de Análises Ambientais, Universidade Federal do Tocantins, Rua Badejos, Gurupi, TO, Brazil.
Chemosphere. 2022 Jul;299:134472. doi: 10.1016/j.chemosphere.2022.134472. Epub 2022 Mar 31.
Atmospheric deposition is a key mode of iron (Fe) input to ocean regions where low concentrations of this micronutrient limit marine primary production. Various natural particles (e.g., mineral dust, volcanic ash) and anthropogenic particles (e.g., from industrial processes, biomass burning) can deliver Fe to the ocean, and assessment of their relative importance in supplying Fe to seawater requires knowledge of both their deposition flux and their Fe solubility (a proxy for Fe bioavailability). Iron isotope (Fe, Fe, Fe, Fe) analysis is a potential tool for tracing natural and anthropogenic Fe inputs to the ocean. However, it remains uncertain how the distinct Fe isotopic signatures (δFe) of these particles may be modified by physicochemical processes (e.g., acidification, photochemistry, condensation-evaporation cycles) that are known to enhance Fe solubility during atmospheric transport. In this experimental study, we measure changes over time in both Fe solubility and δFe of a Tunisian soil dust and an Fe-Mn alloy factory industrial ash exposed under irradiation to a pH 2 solution containing oxalic acid, the most widespread organic complexing agent in cloud- and rainwater. The Fe released per unit surface area of the ash (∼1460 μg Fe m) is ∼40 times higher than that released by the dust after 60 min in solution. Isotopic fractionation is also observed, to a greater extent in the dust than the ash, in parallel with dissolution of the solid particles and driven by preferential release of Fe into solution. After the initial release of Fe, the re-adsorption of A-type Fe-oxalate ternary complexes on the most stable surface sites of the solid particles seems to impair the release of the heavier Fe isotopes, maintaining a relative enrichment in the light Fe isotope in solution over time. These findings provide new insights on Fe mobilisation and isotopic fractionation in mineral dust and industrial ash during atmospheric processing, with potential implications for ultimately improving the tracing of natural versus anthropogenic contributions of soluble Fe to the ocean.
大气沉降是铁（Fe）输入海洋的主要方式之一，而海洋中这种微量元素的浓度较低会限制海洋初级生产力。各种天然颗粒（如矿物尘、火山灰）和人为颗粒（如工业过程、生物质燃烧）都可以将 Fe 输送到海洋，评估它们在向海水提供 Fe 方面的相对重要性需要了解它们的沉积通量及其 Fe 溶解度（Fe 生物可利用性的指标）。铁同位素（Fe、Fe、Fe、Fe）分析是追踪海洋中自然和人为 Fe 输入的潜在工具。然而，这些颗粒的独特 Fe 同位素特征（δFe）可能会通过物理化学过程（如酸化、光化学、凝结-蒸发循环）发生变化，这些过程已知会在大气传输过程中提高 Fe 的溶解度，目前仍不确定这一点。在这项实验研究中，我们测量了在 pH 2 溶液中暴露于辐射下的突尼斯土壤尘和 Fe-Mn 合金厂工业灰的 Fe 溶解度和 δFe 随时间的变化，该溶液中含有草酸，这是云中和雨水中最广泛的有机络合剂。与尘埃相比，灰烬单位表面积释放的 Fe 量（约 1460μg Fe m）在 60 分钟后溶解在溶液中的 Fe 释放量高约 40 倍。还观察到同位素分馏，在尘埃中比在灰烬中更为明显，与固体颗粒的溶解平行，并由 Fe 优先释放到溶液中驱动。在 Fe 的初始释放之后，A 型 Fe-草酸三元配合物重新吸附到固体颗粒最稳定的表面位置似乎会阻碍较重 Fe 同位素的释放，从而随着时间的推移保持溶液中轻 Fe 同位素的相对富集。这些发现为大气处理过程中矿物尘和工业灰中铁的迁移和同位素分馏提供了新的见解，对最终改善对海洋中可溶性 Fe 的自然与人为贡献的追踪具有潜在意义。
