Iron is a key micronutrient controlling phytoplankton growth in vast regions of the global ocean. Despite its importance, uncertainties remain high regarding external iron source fluxes and internal cycling on a global scale. In this study, we used a global dissolved iron data set, including GEOTRACES measurements, to constrain source and scavenging fluxes in the marine iron component of a global ocean biogeochemical model. Our model simulations tested three key uncertainties: source inputs of atmospheric soluble iron deposition (varying from 1.4 to 3.4 Gmol/yr), reductive sedimentary iron release (14–117 Gmol/yr), and compared a variable ligand parameterization to a constant distribution. In each simulation, scavenging rates were tuned to reproduce the observed global mean iron inventory for consistency. The variable ligand parameterization improved the global model-data misfit the most, suggesting that heterotrophic bacteria are an important source of ligands to the ocean. Model simulations containing high source fluxes of atmospheric soluble iron deposition (3.4 Gmol/yr) and reductive sedimentary iron release (114 Gmol/yr) further improved the model most notably in the surface ocean. High scavenging rates were then required to maintain the iron inventory resulting in relatively short surface and global ocean residence times of 0.83 and 7.5 years, respectively. The model simulates a tight spatial coupling between source inputs and scavenging rates, which may be too strong due to underrepresented ligands near source inputs, contributing to large uncertainties when constraining individual fluxes with dissolved iron concentrations. Model biases remain high and are discussed to help improve global marine iron cycle models.

中文翻译：

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使用海洋生物地球化学模型中的 GEOTRACES 溶解铁测量限制全球海洋铁源和配体介导的清除通量

铁是控制全球海洋广大地区浮游植物生长的关键微量营养素。尽管它很重要，但在全球范围内，外部铁源通量和内部循环的不确定性仍然很高。在这项研究中，我们使用了全球溶解铁数据集，包括 GEOTRACES 测量，来限制全球海洋生物地球化学模型的海洋铁成分中的来源和清除通量。我们的模型模拟测试了三个关键的不确定性：大气可溶性铁沉积的源输入（从 1.4 到 3.4 Gmol/yr）、还原性沉积铁释放（14-117 Gmol/yr），并将可变配体参数化与恒定分布进行比较。在每个模拟中，清除率被调整以重现观察到的全球平均铁库存以保持一致性。可变配体参数化改善了全球模型数据最不匹配的情况，这表明异养细菌是海洋配体的重要来源。包含大气可溶性铁沉积（3.4 Gmol/yr）和还原性沉积铁释放（114 Gmol/yr）的高源通量的模型模拟进一步改进了模型，最显着的是在表层海洋中。然后需要高清除率来维持铁库存，导致相对较短的表面和全球海洋停留时间分别为 0.83 年和 7.5 年。该模型模拟了源输入和清除率之间的紧密空间耦合，由于源输入附近的配体代表性不足，这可能太强，从而在用溶解铁浓度限制单个通量时产生很大的不确定性。