Fe Behavior and Bioavailability in Sub-aerial Runoff into the Ross Sea

浮游植物或微小的海洋藻类是碳循环的重要组成部分，可以通过将大气中的碳转移到海洋中来降低大气中二氧化碳的含量。南大洋浮游植物的浓度经常受到海洋铁供应的限制。这反过来又影响了碳从大气向海洋转移的速度。南大洋中铁的主要来源是被侵蚀的大陆岩石。为了预测未来南大洋浮游植物的浓度及其对碳循环的后续影响，了解陆地冰川融化加剧导致的南大洋目前和未来的铁来源是必要的。南大洋的铁的一个鲜为人知的来源是来自无冰地区的流输入，如南极洲的麦克默多干谷。如果冰川退缩，这种铁的来源可能会变得更大。这项研究调查了麦克默多干谷河流直接进入南大洋的铁的来源和数量。因为不是所有形式的铁都能被浮游植物利用，所以将进行实验来确定浮游植物可利用的铁以及铁如何与海水混合。该项目的沉浸式360度视频、信息图表和教育视频将在社交媒体、学校和科学活动以及城市科学中心分享。在南大洋（SO）有过量的宏量营养素，但区域初级生产有限或共同有限，由于铁。向海洋中添加铁会影响生物化学循环，增加初级产量，并影响SO中浮游植物群落的结构和组成。到SO的铁通量在全球范围内是重要的，因为增加的铁施肥导致增加的碳固存，这对增加的大气二氧化碳分压起负反馈作用。南极沿海地区潜在生物可利用铁的一个来源是南极洲无冰地区的直接空中水流排放，如果陆地冰川退缩，这一来源可能变得更加重要。如果要开发出更好的碳循环和大气化学预测模型，就必须了解铁的来源、性质、潜在命运和进入SO的通量。该项目将研究控制溶解铁排入罗斯海的河流过程和特征，包括光还原、温度和与有机物的络合。这项新研究将量化颗粒铁的生物利用度和南极流入SO的河流中溶解铁的生物利用度。将对溶解的铁进行现场形态测量，使用高分辨率光谱确定颗粒铁的形态，将与沿海海水进行混合实验，并通过海洋生物分析确定铁的生物利用度。该项目将为两名学生提供宝贵的南极实地经验，并通过与K-12学校、公共STEM活动、城市科学中心和强大的社交媒体的现有合作关系，接触到数千人。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Phytoplankton, or microscopic marine algae, are an important part of the carbon cycle and can lower the rates of atmospheric carbon dioxide by transferring the atmospheric carbon into the oceans. The concentration of phytoplankton in the Southern Ocean is regularly limited by the availability of marine iron. This in turn influences the rate of carbon transfer from the atmosphere to the ocean. The primary source of iron in the Southern Ocean is eroded continental rock. Understanding the current and future sources of iron to the Southern Ocean as a result of increased melting of terrestrial glaciers is necessary for predicting future concentrations of Southern Ocean phytoplankton and the subsequent influence on the carbon cycle. A poorly understood source of iron to the Southern Ocean is stream input from ice-free regions such as the McMurdo Dry Valleys in Antarctica. This source of iron is likely to become larger if glaciers retreat. This study investigates the sources and amount of iron transported by McMurdo Dry Valley streams directly into the Southern Ocean. Because not all forms of iron can be used by phytoplankton, experiments will be performed to determine how available iron is to phytoplankton and how iron mixes with seawater. Immersive 360-degree video, infographics, and educational videos of findings from this project will be shared on social media, at schools and science events, and in an urban science center.In the Southern Ocean (SO) there is an excess of macronutrients but regional primary production is limited or co-limited due to iron. An addition of iron to the ocean will affect biochemical cycles, increase primary production, and affect the structure and composition of phytoplankton communities in the SO. Iron flux to the SO is globally significant, as increased Fe fertilization leads to increased carbon sequestration which acts as a negative feedback to increased atmospheric pCO2. One source of potentially bioavailable iron to the coastal regions of the SO is from direct sub-aerial stream discharge in ice-free areas of Antarctica, a source that may become more important if terrestrial glaciers retreat. It is imperative to understand the source, nature, potential fate, and flux of iron to the SO if better predictive models for the carbon cycle and atmospheric chemistry are to be developed. This project will investigate in-stream processes and characteristics controlling dissolved iron draining into the Ross Sea including photoreduction, temperature, and complexation with organic matter. The novel study will quantify bioavailability of particulate iron and bioavailability of dissolved iron in Antarctic in streams draining into the SO. On-site speciation measurements will be performed on dissolved iron species, particulate iron speciation will be determined using high-resolution spectroscopy, mixing experiments will be performed with coastal marine water, and the bioavailability of Fe will be determined through marine bioassays. This project will provide two students with valuable Antarctic field experience and reach thousands of individuals through existing partnerships with K-12 schools, public STEM events, an urban science center, and a strong social media presence.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.