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

铁是海洋生物必需的微量营养素，其分布强烈影响浮游植物初级生产力的大小，从而影响海洋的碳吸收。虽然我们正在慢慢了解海洋中溶解铁目前的全球分布情况，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(例如灰尘)预计将随着正在进行的气候变化而发生强烈变化，而另一些则不会。因此，具体来源的相关性有多大的不确定性严重阻碍了我们预测海洋铁循环和初级生产将如何应对气候变化的能力。一个限制不同铁源作用的新工具是研究海洋中溶解铁的稳定同位素组成。由于不同的外部铁源具有不同的同位素比率，这种组成原则上可以用来推断不同来源的相对贡献。然而，海洋内部不同形式的铁(溶解的和非生物/生物颗粒、氧化还原状态)之间的转化过程可以在其同位素之间进行分馏，物理过程(运输和扩散)也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，将扩展基于我以前工作的全球铁生物地球化学模型，明确表示同位素效应，以揭示影响海洋中溶解铁同位素组成的不同过程的作用。再加上国际地质勘测系统计划内获得的越来越多的铁同位素测量，这将使我们能够更好地量化主要外部铁源的大小和相对作用，从而能够对未来海洋初级生产力做出更可靠的预测。

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.