Postdoctoral Fellowship: OPP-PRF: Understanding the Role of Specific Iron-binding Organic Ligands in Governing Iron Biogeochemistry in the Southern Ocean

铁是全球海洋中的一种基本营养物质，浮游植物需要铁来执行几项基本的细胞功能。在南大洋，铁尤其稀缺，对初级生产和由此产生的表层海洋的二氧化碳吸收起着主要控制作用。南大洋中的大多数溶解铁与一种称为配体的有机铁结合化合物的复杂混合物结合。这些配体的浓度和特性控制着铁的生物利用度、反应性和运输。胞外多糖(EPS)是一类特别重要的配体，由当地微生物群落在高浓度下产生，具有各种功能，包括作为冷冻保护剂。尽管已知EPS的重要性，但大多数铁结合配体的研究都集中在总配体浓度或铁载体的鉴定上。铁载体是一种作为微生物铁获取策略而产生的铁结合小分子，由于其异常高的铁结合亲和力，被认为在铁循环中扮演着不成比例的角色。该项目将必要的EPS浓度测量添加到2023年美国地理跟踪公司GP17-ANT阿蒙森海探险队的样本子集中。该项目首次整合了EPS、铁载体和大宗配体测量，从而为有机配体的组成如何决定南大洋的铁供应和命运提供了前所未有的见解。研究计划涉及实地和实验相结合的方法。用于电化学EPS分析的现场样品将在从冰缘到开阔水域的GP17-ANT横断面上采集。之前资助的大宗配基浓度和铁载体鉴定的配对样本也将沿着同一横断面进行。这三项分析的结果将结合起来评估EPS和铁载体对总配位体的相对贡献，并解释它们对该地区铁生物地球化学循环的影响。将进行实验室实验，以评估EPS是否改变海水中铁载体和铁的粒度分馏，从而将这两种物种穿梭到颗粒相。然后，实验结果将被用来解释综合的现场数据，并提高对配体对阿蒙森海中铁的运输和生物有效性的影响的理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Iron is an essential nutrient in the global ocean, required by phytoplankton to perform several essential cellular functions. In the Southern Ocean, iron is especially scarce and exerts a primary control on primary production and resulting CO2 uptake by the surface ocean. Most dissolved iron in the Southern Ocean is bound to a complex mixture of organic iron-binding compounds, called ligands. The concentrations and identities of these ligands control iron bioavailability, reactivity, and transport. Exopolysaccharides (EPS) are a particularly important group of ligands that are produced in high concentrations by local microbial communities for a variety of functions, including as cryoprotectants. Despite the known importance of EPS, most iron-binding ligand studies focus on total ligand concentrations or siderophore identification. Siderophores, small iron-binding molecules produced as a microbial iron acquisition strategy, are thought to play a disproportionate role in iron cycling due to their unusually high iron-binding affinities. This project adds essential EPS concentration measurements to a subset of samples from the 2023 U.S. GEOTRACES GP17-ANT expedition to the Amundsen Sea. This project integrates EPS, siderophores and bulk ligand measurements for the first time, thereby offering unprecedented insights into how the composition of organic ligands governs the supply and fate of iron to the Southern Ocean.The research plan involves a combination of field and experimental approaches. Field samples for electrochemical EPS analysis will be collected on a GP17-ANT transect spanning from the ice edge to open water. Previously funded paired samples of bulk ligand concentrations and siderophore identification will also be taken along the same transect. Results from the three analyses will be combined to assess the relative contributions of EPS and siderophores to the total ligand pool and interpret their impact on iron biogeochemical cycling in the region. Lab experiments will be performed to evaluate whether EPS alters the size fractionation of siderophores and iron in seawater, shuttling both species into the particulate phase. Experimental results will then be used to interpret the integrated field data and improve understanding of the impact of ligands on iron transport and bioavailability in the Amundsen Sea.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.