Iron (Fe), a micronutrient for algal growth, and plutonium (Pu), an anthropogenic radionuclide, share some common features. This includes similar oceanic distributions when different input modes are taken into account, as well as their chemical behavior, such as a high affinity to natural organic matter (NOM). The NOM produced by various phytoplankton communities can potentially influence Fe cycling in the ocean, and likely also influence the transport behavior of Pu. We conducted laboratory incubation experiments using the coccolithophore Emiliania huxleyi and the diatom Skeletonema costatum, in the presence of ⁵⁹Fe and ²³⁸Pu as radiotracers, in order to differentiate Fe and Pu uptake by extracellular exopolymeric substances (EPS) and intracellular biopolymers. The Fe and Pu distributions in select organic compound classes produced by these two types of phytoplankton, including proteins, total carbohydrates (TCHO) and uronic acids (URA), were compared. Our results indicated that most of the Fe and Pu (>95%) were found concentrated in E. huxleyi-derived non-attached EPS, while much less (<2%) was present in the intracellular fraction of E. huxleyi. In contrast, in the diatom S. costatum, Fe and Pu were both distributed with EPS > intracellular biopolymers > outer cell covering (i.e., frustule). In fact, over 50% of the Fe was concentrated in S. costatum-derived attached EPS and intracellular biopolymers. The diatom derived Fe-EPS complexes were more hydrophobic, with stronger tendency to aggregate in seawater. Fe binding to biopolymers in both E. huxleyi and S. costatum cultures was related to URA concentrations, but the overall distribution of URA between these two phytoplankton species was different (e.g., high intracellular abundance of URA in S. costatum but low intracellular URA abundance in E. huxleyi). Our findings suggest that the presence of URA on cellular surfaces of S. costatum (i.e., attached EPS) and its high intracellular fraction could be an indicator for Fe transport from the surrounding seawater to the diatom cells. However, for the coccolithophore E. huxleyi, Fe was not efficiently taken up during its growth. Instead, the more hydrophilic non-attached EPS (i.e., low protein/TCHO ratio) produced by E. huxleyi could have stabilized Fe in the colloidal form as Fe-EPS complexes. Similar partitioning behavior of Fe and Pu suggests that Pu isotopes can potentially serve as a tracer for Fe biogeochemistry in the ocean.

铁（Fe）是藻类生长的微量营养元素，and（Pu）是人为放射性核素，具有一些共同的特征。当考虑到不同的输入模式时，这包括相似的海洋分布及其化学行为，例如对天然有机物（NOM）的高亲和力。各种浮游植物群落产生的NOM可能会影响海洋中铁的循环，还可能影响Pu的运输行为。我们在⁵⁹ Fe和²³⁸ Fe的存在下，使用coccolithophore Emiliania huxleyi和硅藻Skeletonema costatum进行了实验室培养实验。Pu作为放射性示踪剂，以区分胞外聚合物（EPS）和胞内生物聚合物对Fe和Pu的吸收。比较了这两种浮游植物所产生的特定有机化合物类别中的Fe和Pu分布，包括蛋白质，总碳水化合物（TCHO）和糖醛酸（URA）。我们的结果表明，大多数的Fe和Pu（> 95％）都集中在赫黎来源的未附着EPS中，而在赫。黎的细胞内部分中则少得多（<2％）。相反，在硅藻S.costatum中，Fe和Pu均以EPS>细胞内生物聚合物>细胞外覆盖物（即截头壳）分布。实际上，超过50％的铁都集中在肋骨沙门氏菌中。衍生的附着EPS和细胞内生物聚合物。硅藻衍生的Fe-EPS复合物疏水性更高，在海水中聚集的趋势更强。铁与虎杖和链球菌培养物中生物聚合物的结合与URA浓度有关，但是这两种浮游植物物种之间URA的总体分布是不同的（例如，肋骨中URA的细胞内丰度高而胞内URA丰度低在E. huxleyi中）。我们的研究结果表明在肋链球菌的细胞表面上存在URA（即附着的EPS）及其较高的细胞内分数可能是Fe从周围海水向硅藻细胞运输的指标。然而，对于coccolithophore huxleyi，Fe在其生长过程中并未被有效吸收。取而代之的是，赫x黎大肠杆菌产生的亲水性更高的非附着EPS（即低蛋白质/ TCHO比）可以将Fe以胶体形式稳定为Fe-EPS复合物。Fe和Pu的类似分配行为表明，Pu同位素可以作为海洋中Fe生物地球化学的示踪剂。