Although iron (Fe) is a key regulator of primary production over much of the ocean, many components of the marine iron cycle are poorly constrained, which undermines our understanding of climate change impacts. In recent years, a growing number of studies (often part of GEOTRACES) have used Fe isotopic signatures (δ⁵⁶Fe) to disentangle different aspects of the marine Fe cycle. Characteristic δ⁵⁶Fe endmembers of external sources and assumed isotopic fractionation during biological Fe uptake or recycling have been used to estimate relative source contributions and investigate internal transformations, respectively. However, different external sources and fractionation processes often overlap and act simultaneously, complicating the interpretation of oceanic Fe isotope observations. Here we investigate the driving forces behind the marine dissolved Fe isotopic signature (δ⁵⁶Fe_diss) distribution by incorporating Fe isotopes into the global ocean biogeochemical model PISCES. We find that distinct external source endmembers acting alongside fractionation during organic complexation and phytoplankton uptake are required to reproduce δ⁵⁶Fe_diss observations along GEOTRACES transects. δ⁵⁶Fe_diss distributions through the water column result from regional imbalances of remineralization and abiotic removal processes. They modify δ⁵⁶Fe_diss directly and transfer surface ocean signals to the interior with opposing effects. Although attributing crustal compositions to sedimentary Fe sources in regions with low organic carbon fluxes improves our isotope model, δ⁵⁶Fe_diss signals from hydrothermal or sediment sources cannot be reproduced accurately by simply adjusting δ⁵⁶Fe endmember values. This highlights that additional processes must govern the exchange and/or speciation of Fe supplied by these sources to the ocean.

中文翻译：

---

全球海洋模型对铁同位素循环的限制

尽管铁 (Fe) 是海洋大部分地区初级生产的关键调节剂，但海洋铁循环的许多组成部分受到的限制很差，这破坏了我们对气候变化影响的理解。近年来，越来越多的研究（通常是 GEOTRACES 的一部分）使用 Fe 同位素特征（δ ⁵⁶ Fe）来解开海洋 Fe 循环的不同方面。特性 δ ⁵⁶外部来源的 Fe 端元和生物 Fe 吸收或回收过程中假定的同位素分馏已分别用于估计相对来源贡献和研究内部转化。然而，不同的外部来源和分馏过程经常重叠并同时作用，使海洋铁同位素观测的解释复杂化。在这里，我们通过将 Fe 同位素纳入全球海洋生物地球化学模型 PISCES来研究海洋溶解的 Fe 同位素特征 (δ ⁵⁶ Fe _diss ) 分布背后的驱动力。我们发现，在有机络合和浮游植物吸收过程中，不同的外部源端元与分馏一起作用是复制 δ ⁵⁶ Fe _{diss所必需的。}沿 GEOTRACES 样带的观测。δ ⁵⁶ Fe _diss在水柱中的分布是再矿化和非生物去除过程的区域不平衡造成的。它们直接修改 δ ⁵⁶ Fe _diss并将表面海洋信号传输到内部，产生相反的效果。尽管将地壳成分归因于有机碳通量低的地区的沉积铁源改进了我们的同位素模型，但仅通过调整 δ ⁵⁶就无法准确再现来自热液或沉积物源的δ ⁵⁶ Fe _diss信号Fe 端元值。这凸显了额外的过程必须控制这些来源向海洋提供的铁的交换和/或物种形成。