A survey of Fe-isotope fractionation in the marine biogeochemical cycle

尽管铁对浮游生物生产和全球碳循环的重要性，但海洋可溶性铁的来源缺乏量化，海洋铁的生物地球化学循环也知之甚少。我们建议使用新的Fe同位素系统来验证这个循环。这是可能的，因为在许多主要的地球化学过程中，Fe同位素以一种特有的方式发生断裂。我们以前的沉积活性铁的研究表明，在早期的海洋成岩作用的系统同位素趋势，并建议，溶解的铁逃逸回大海具有独特的和非常轻的同位素组成。在两个通量，大陆铁和成岩改性铁的简单情况下，海水的同位素组成应反映各自的混合比例。此外，过程反应物和产物的Fe同位素组成取决于给定反应的完成程度，因此可以指示特定地球化学过程发生的程度。我们试图研究海洋Fe同位素分馏在整个海洋地球化学循环的Fe。大部分的研究将在波罗的海，其中包括海洋铁循环的所有主要方面，并占主导地位的溶解铁只有两个来源。波罗的海的高铁负荷将保持样本量可控，并支持方法开发。铁同位素分馏将在河口混合，海洋颗粒形成和海洋成岩作用和水柱的目的是开发一个适用于公海的工具箱进行研究。

Sources of soluble Fe to the ocean are poorly quantified and the marine biogeochemical cycle of Fe is poorly understood despite the importance of Fe for plankton production and the global carbon cycle. We propose to use the novel Fe isotope system to characterise this cycle. This is now possible because Fe isotopes fractionate in a characteristic way during many of the principal biogeochemical processes. Our previous study of sedimentary reactive Fe shows a systematic isotopic trend during early marine diagenesis and suggests that the dissolved Fe escaping back into the sea has a unique and very light isotopic composition. In the simple case of two fluxes, continental Fe and diagenetically modified Fe, the isotopic composition of seawater should reflect the respective mixing proportions. In addition, the Fe isotopic composition of process reactant and product depends on the completeness of a given reaction and may therefore indicate to what extent a particular biogeochemical process takes place. We seek to investigate marine Fe isotope fractionation in the full marine biogeochemical cycle of Fe. Much of the study will be done in the Baltic Sea, which comprises all principal aspects of the marine Fe cycle and is dominated by only two sources of dissolved Fe. The high Fe load of the Baltic Sea will keep sample sizes manageable and support method development. Fe isotope fractionation will be investigated during estuarine mixing, marine particle formation and marine diagenesis and in the water column with the aim to develop a toolbox applicable to the open ocean.