Collaborative research: Using individual amino acids N isotopes in sinking particles and surficial sediments to reconstruct euphotic zone N sources and trophic structure

氮是海洋表层的一种限制性营养物质。固定氮(N)，如硝酸盐，控制海洋植物和藻类对大气二氧化碳的吸收和有机物的产生。氮的有效性、利用模式和海洋表面的生物群落结构有助于确定有机物质传递给高等生物的数量。氮的可用性也控制着有多少有机物沉入深水。该项目将重建加州湾、赤道太平洋和马尾藻海表层水域过去氮的来源、使用模式和营养结构。来自科珀斯克里斯蒂的德克萨斯农工大学和马萨诸塞大学达特茅斯分校的主要研究人员使用的工具是单个氨基酸的氮同位素比率。研究人员将测量沉积物捕集器收集的下沉颗粒样本的同位素比率，例如马尾藻海海洋通量计划使用的沉淀物捕集器。本研究将培养稳定同位素生物地球化学和海洋学方面的研究生。该项目还将为麦克奈尔项目的学生提供研究经费。麦克奈尔的学生来自代表性不足和经济困难的背景，他们在德克萨斯农工大学科珀斯克里斯蒂分校攻读STEM领域的学位，这是一所西班牙裔和少数族裔服务机构。该项目的数据将通过生物和化学海洋学数据管理办公室（www.bco-dmo.org）向公众提供。人们对利用沉积物和珊瑚骨架中保存的蛋白质物质中释放的氨基酸的复合特定N同位素比率来重建过去气候强迫的氮源变化、利用模式和光带群落结构非常感兴趣。然而，目前尚未证实：1)发光带中产生的单个氨基酸的氮同位素比率是否通过沉降颗粒保真地输送到深海珊瑚和沉积物中；2)沉积有机质中释放的单个氨基酸的氮同位素比率是否因成岩作用而改变。通过对长期收集的沉积物捕集器材料的分析，该项目试图验证单个氨基酸中的氮同位素比率反映了1)加利福尼亚湾、赤道太平洋和马尾藻海中氮来源、利用模式和营养结构的整体空间差异；2)氮来源、利用模式、营养结构的时间变化。由于季节性上升流和/或厄尔尼诺-南方涛动，加利福尼亚湾和赤道太平洋内的营养结构。本研究还将测试三个地点的沉积有机质中总水解氨基酸的氮同位素比率是否保留沉降颗粒携带的不变氮同位素模式。该项目将首次比较沉积物捕集器样品和深海含氧区表层沉积物中氨基酸的氮稳定同位素比值，以验证深海沉积物中总水解氨基酸是否保留了上覆泛光带中产生的未改变的氮同位素信号，这将为解决阻碍古氮循环重建的总体N同位素比值的成岩蚀变提供新的思路。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。

Nitrogen is a limiting nutrient over most of the surface ocean. Fixed nitrogen (N) such as nitrate controls absorption of atmospheric carbon dioxide and production of organic matter by marine plants and algae. Nitrogen availability, use patterns, and biological community structure in the surface ocean help determine the amount of organic matter passed onto higher organisms. Nitrogen availability also controls how much organic matter sinks into deep waters. This project will reconstruct past sources of nitrogen, use patterns, and trophic structures in surface waters of the Gulf of California, equatorial Pacific, and Sargasso Sea. The tool employed by the principal investigators from Texas A&M University in Corpus Christi and University of Massachusetts Dartmouth is nitrogen isotope ratios of individual amino acids. The investigators will measure isotope ratios in sinking particle samples collected by sediment traps such as those used by the Ocean Flux Program in the Sargasso Sea. This study will train graduate students in stable isotope biogeochemistry and oceanography. This project will also provide research funds for students in the McNair program. McNair students come from underrepresented and economically challenged backgrounds to pursue degrees in STEM fields at Texas A&M University Corpus Christi, a Hispanic and Minority Serving Institution. Data from this project will be made available to the public through the Biological and Chemical Oceanography-Data Management Office (www.bco-dmo.org).There is great interest in reconstructing past climate-forced variations in nitrogen sources, their patterns of utilization, and euphotic zone community structure using compound specific N isotope ratios in amino acids liberated from preserved proteinaceous materials in sediments and coral skeletons. However, it has not yet been verified whether 1) the nitrogen isotope ratios of individual amino acids produced in the euphotic zone are transported with fidelity by sinking particles to deep-sea corals and sediments and 2) the nitrogen isotope ratios of individual amino acids liberated from sedimentary organic matter have been altered by diagenesis. Through analysis of sediment trap material collected over time, this project seeks to verify that nitrogen isotope ratios in individual amino acids reflect the 1) overall spatial contrast in N sources, utilization patterns, and trophic structures among the Gulf of California, equatorial Pacific, and Sargasso Sea and 2) temporal variations in nitrogen sources, utilization patterns, and trophic structures within both the Gulf of California and equatorial Pacific due to seasonal upwelling and/or El Nino-Southern Oscillation. This study will also test if the nitrogen isotope ratios of total hydrolysable amino acids in sedimentary organic matter from the three locations retain the unaltered nitrogen isotope patterns carried by sinking particles. This project will, for the first time, compare nitrogen stable isotope ratios in amino acids collected from sediment trap samples with surficial sediments from deep-sea oxic sites to verify whether total hydrolysable amino acids in deep-sea sediments preserve unaltered nitrogen isotope signals produced in overlying euphotic zone, which can provide insights on addressing diagenetic alteration of bulk N isotope ratios that have hindered paleo-nitrogen cycle reconstruction.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.