Biopolymers as carrier phases for selected natural radionuclides (of Th, Pa, Pb, Po, Be) in diatoms and coccolithophores

与粒子有关的天然放射性同位素主要通过二氧化硅和碳酸盐压载粒子运输到海底，因此可以用作粒子运输的示踪剂。 Th（IV）、Pa（IV，V）、Po（IV）、Pb（II）和Be（II）放射性核素是海洋学研究中的重要替代物，在古海洋学研究中用于示踪颗粒和胶体循环，估算颗粒有机碳的输出通量，示踪海气交换、古生产力和/或海洋环流。 尽管示踪剂方法被认为是常规的，但在某些情况下，数据的解释或有效性已成为有争议的，主要是由于无机代理和有机载体分子的不确定性。 最近的研究表明，清洁硅藻细胞壳和纯二氧化硅颗粒，吸附天然放射性核素的程度低得多（1-2个数量级）比整个硅藻细胞（有或没有壳）。 构建硅质或钙质壳的浮游植物，如硅藻和颗石藻，通过生物矿化过程使用生物聚合物作为纳米级模板组装。 这些模板可以作为放射性核素和稳定金属的可能载体。 在这个项目中，德克萨斯A M大学加尔维斯顿的一个研究小组假设，放射性核素的吸附是由选择性生物聚合物控制的，这些生物聚合物与生物蛋白石（硅藻），CaCO 3（颗石藻）和附着的外聚合物物质（EPS）有关，而不是纯矿物相。 为了实现这一想法，他们研究的主要目标将包括分离、鉴定和分子水平表征单个生物聚合物（例如，多糖、糖醛酸、蛋白质、氢醌、异羟肟酸铁载体等）在实验室生长的硅藻和颗石藻培养物中，它们负责结合附着在细胞上或生物蛋白石或CaCO 3基质中以及附着的EPS混合物中的不同放射性核素（Th、Pa、Pb、Po和Be）。 将进行实验室规模的放射性标记实验，并将采用不同的分离技术和表征技术。智力优势：本研究将有助于阐明硅藻和球石模板生长的分子基础，以及EPS在海洋中清除天然放射性核素的作用，并有助于解决不同天然放射性同位素（230，234 Th，231 Pa，210 Po，210 Pb和7，10 Be）在海洋示踪应用中的争议。 拟议的跨学科研究项目将需要采用仪器方法，在分子水平上对这些与放射性核素有关的载体分子进行表征。这项研究的结果将有助于了解硅藻和球石对放射性核素的生物介导的海洋清除，这对海洋中的碳循环很重要，并将有助于改进对通过实地研究，特别是通过GEOTRACES计划获得的数据的解释。 这个新项目将加强TAMUG为博士后，研究生和本科生提供的培训计划。 最后，结果将被整合在大学课程和外展活动在得克萨斯州A M大学，包括NSF-REU，海营，长老宿舍和展览在当地的科学博览会和互动与其课外计划从事9-12年级的学生从传统上代表性不足的群体。

Particle-associated natural radioisotopes are transported to the ocean floor mostly via silica and carbonate ballasted particles, allowing their use as tracers for particle transport. Th(IV), Pa (IV,V), Po(IV), Pb(II) and Be(II) radionuclides are important proxies in oceanographic investigations, used for tracing particle and colloid cycling, estimating export fluxes of particulate organic carbon, tracing air-sea exchange, paleoproductivity, and/or ocean circulation in paleoceanographic studies. Even though tracer approaches are considered routine, there are cases where data interpretation or validity has become controversial, largely due to uncertainties about inorganic proxies and organic carrier molecules. Recent studies showed that cleaned diatom frustules and pure silica particles, sorb natural radionuclides to a much lower extent (by 1-2 orders of magnitude) than whole diatom cells (with or without shells). Phytoplankton that build siliceous or calcareous shells, such as the diatoms and coccolithophores, are assembled via bio-mineralization processes using biopolymers as nanoscale templates. These templates could serve as possible carriers for radionuclides and stable metals. In this project, a research team at the Texas A & M University at Galveston hypothesize that radionuclide sorption is controlled by selective biopolymers that are associated with biogenic opal (diatoms), CaCO3 (coccolithophores) and the attached exopolymeric substances (EPS), rather than to pure mineral phase. To pursue this idea, the major objectives of their research will include separation, identification and molecular-level characterization of the individual biopolymers (e.g., polysaccharides, uronic acids, proteins, hydroquinones, hydroxamate siderophores, etc.) that are responsible for binding different radionuclides (Th, Pa, Pb, Po and Be) attached to cells or in the matrix of biogenic opal or CaCO3 as well as attached EPS mixture, in laboratory grown diatom and coccolithophore cultures. Laboratory-scale radiolabeling experiments will be conducted, and different separation techniques and characterization techniques will be applied. Intellectual Merit : It is expected that this study will help elucidate the molecular basis of the templated growth of diatoms and coccoliths, EPS and their role in scavenging natural radionuclides in the ocean, and help resolve debates on the oceanographic tracer applications of different natural radioisotopes (230,234Th, 231Pa, 210Po, 210Pb and 7,10Be). The proposed interdisciplinary research project will require instrumental approaches for molecular-level characterization of these radionuclides associated carrier molecules.Broader Impacts: The results of this study will be relevant for understanding biologically mediated ocean scavenging of radionuclides by diatoms and coccoliths which is important for carbon cycling in the ocean, and will contribute to improved interpretation of data obtained by field studies especially through the GEOTRACES program. This new program will enhance training programs at TAMUG for postdocs, graduate and undergraduate students. Lastly, results will be integrated in college courses and out-reach activities at Texas A&M University, including NSF-REU, Sea Camp, Elder Hostel and exhibits at the local science fair and interaction with its after-school program engaging Grade 9-12 students from groups traditionally underrepresented.