Constraining the magnitude of different iron sources to the ocean with a model of the stable isotopic composition of dissolved and particulate iron

铁是海洋生物区系必需的微量营养元素，其分布强烈影响浮游植物初级生产力的大小，从而影响海洋中的碳吸收。虽然我们正在慢慢地了解目前全球海洋中溶解铁的分布情况，但对于这种分布背后的机制，特别是不同外部铁源（风成尘、海洋沉积物、热液和河流输入）对海洋的相对作用，仍然没有达成共识。其中一些（如灰尘）预计会随着气候变化而发生强烈变化，而其他则不会。因此，具体来源的相关性的不确定性严重阻碍了我们了解海洋铁循环和初级生产将如何应对气候变化的能力。研究海洋溶解铁的稳定同位素组成是限制不同铁源作用的一个新工具。由于不同的外部铁源具有不同的同位素比率，因此该组成原则上可用于推断不同来源的相对贡献。然而，在海洋内部不同形式（溶解和非生物/生物粒子，氧化还原状态）之间转换铁的过程可以在其同位素和物理过程（运输和扩散）之间发生断裂，也会影响铁的同位素组成。这使得有必要将铁同位素数据的解释与海洋中铁循环的模型结合起来。在拟议的项目中，基于我以前的工作的铁的全球海洋地球化学模型将被扩展，明确表示同位素效应，以解开影响海洋中溶解铁的同位素组成的不同过程的作用。再加上在国际GEOTRACES计划中获得的铁同位素测量值越来越多，这将使人们能够更好地量化主要外部铁源的数量和相对作用，从而能够更有力地预测未来海洋初级生产。

Iron is an essential micronutrient for ocean biota, and its distribution strongly affects the magnitude of phytoplankton primary productivity and thus the carbon uptake in the ocean. While we are slowly obtaining a picture of the present global distribution of dissolved iron in the ocean, there is still no consensus on the mechanisms behind this distribution and especially on the relative role of different external iron sources to the ocean (aeolian dust, marine sediments, hydrothermal and riverine inputs). Some of these (e.g. dust) are predicted to change strongly with ongoing climate change while others are not. The uncertainty of how relevant the specific sources are, is therefore severely hampering our ability to prognose how the oceanic iron cycle and primary production will react to climate change. A new tool to constrain the role of the different iron sources is the study of the stable isotopic composition of oceanic dissolved iron. As different external sources of iron have different isotopic ratios, this composition can in principle be used to infer the relative contribution of the different sources. However, processes that transform iron between different forms (dissolved and abiotic/biological particles, redox states) in the interior of the ocean can fractionate between its isotopes and physical processes (transport and diffusion) also affects the isotopic composition of iron. This makes it necessary to combine the interpretation of iron isotope data with a model of iron cycling in the ocean. In the proposed project, a global biogeochemical model of iron based on my previous work will be extended with an explicit representation of isotopic effects to disentangle the role of different processes affecting the isotopic composition of dissolved iron in the ocean. Together with the growing amount of iron isotope measurements obtained within the international GEOTRACES program, this will allow a better quantification of the magnitude and relative role of the main external iron sources, and thus allow more robust prognoses of the future oceanic primary production.