Iron organic speciation in a warmer and a more acidic ocean

铁是陆地和海洋生物必需的有毒元素。它在海水中的浓度低于纳摩尔，限制了估计40%海洋表面的海洋初级生产和碳输出。潜在的生物可利用的铁（即可用于浮游植物生长）被认为主要在溶解部分中，其与有机配体强烈络合（> 99%）。不同铁物种的化学分布或化学形态高度依赖于pH值，并且在较小程度上依赖于温度。由于大气中二氧化碳压力增加，海洋pH值下降和温度升高的影响将改变铁的形态，并可能改变铁与有机配体之间的相互作用，从而影响其整体生物地球化学循环，其在水柱中的停留时间，并最终影响其生物利用度。鉴于铁对地球化学生态系统的重要性，了解其化学形态在酸性更强和更温暖的海洋中可能如何变化至关重要。用于研究铁形态的最灵敏的方法是基于与电活性人工配体结合的铁的汞滴上的伏安吸附。总铁和配体的浓度和稳定常数可以检索，但这些方法往往需要挑剔的实验程序。主要问题是pH调节的要求，这可能会显著改变样品中的铁形态并误导解释。在这个项目中，我们试图开发在pH值灵活的分析方法，以测量在当前和未来的pH/温度值的铁形态，以了解海洋酸化和温度升高对铁形态的影响。

Iron is an essential and toxic element for terrestrial and marine life. It is present at subnanomolar concentration in seawater, limiting the oceanic primary production and carbon export in an estimated 40 % of the ocean surface. The potentially bioavailable iron (i.e. useable for phytoplankton growth) is believed to be mostly in the dissolved fraction, which is strongly complexed (> 99 %) with organic ligands. The chemical distribution of the different iron species, or chemical speciation, is highly dependent on the pH and, to a lesser extent, temperature. The impact of the decrease in ocean pH and increase in temperature, both due to the increasing CO2 pressure in the atmosphere, will modify the iron speciation and potentially the interaction between the iron and the organic ligands, thus affecting its overall biogeochemical cycling, its residence time in the water column and ultimately its bioavailability. In view of the importance of iron on biogeochemical ecosystems, understanding how its chemical speciation is likely to change in more acidic and warmer oceans is of vital importance. The most sensitive methods used to investigate iron speciation are based on the voltammetric adsorption on a mercury drop of iron bound to an electroactive artificial ligand. The total iron and ligands concentration and the stability constants can be retrieved but these methods often require fastidious experimental procedures. The main issue is the requirement of pH adjustment which is potentially modifying significantly the iron speciation in the samples and misleading the interpretation. In this project, we are trying to develop analytical methods flexible in pH to measure the iron speciation at current and future pH/temperature value to gain insights into the effect of ocean acidification and increased temperatures on Fe speciation.