Understanding the nitrogen isotopes of planktonic foraminifera: A modern Sargasso Sea study

了解浮游有孔虫的氮同位素：现代马尾藻海研究

• 批准号: 1060947
• 负责人: Daniel Sigman
• 金额: $ 61.99万
• 依托单位: Princeton University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-04-01 至 2016-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1060947&HistoricalAwards=false
• 关键词: Understanding; nitrogen; isotopes; planktonic; foraminifera

Nitrogen (N) and phosphorus are the two nutrients required in large quantity by phytoplankton in the ocean, and together they limit productivity throughout most of the tropical, subtropical, and temperate ocean. Both the cycling of N and its input/output budget have been argued to control the fertility of the ocean and the ocean's role in setting atmospheric CO2. The CaCO3 tests of foraminifera can represent a substantial fraction of marine sediments and have been used extensively in paleoceanography; they are an obvious target for isotopic analysis of microfossil-bound organic matter. In recent years, researchers at Princeton have developed a protocol for the isotopic analysis of foraminiferal shell-bound N. The current protocol is at least 100 times more sensitive than typical on-line combustion, allowing for rapid progress with a N isotope archive that was previously not feasible to measure. Measurements on surface sediments and a downcore record from the Caribbean show the promise of foraminifera-bound del15N (fb-del15N) to provide both a robust N isotope archive for paleoceanography, and one with a unique potential of richness, given the existence of multiple foraminiferal species with different depth habitats and behaviors. Moreover, the finding from the Caribbean Sea record -- reduced N fixation in ice age Atlantic -- has changed the scientific conversation about the nature of the input/output budget of oceanic fixed N and its potential to change ocean fertility and atmospheric CO2. However, the controls on fb-del15N have not yet been adequately studied.In this project, as a first major step in developing a foundation for the paleoceanographic application of fb-del15N, the same Princeton University team will study its genesis in the water column, transport to the seafloor, and early diagenesis. They will undertake this study in the Sargasso Sea south of Bermuda. This is one of the best studied regions of the ocean, in general and with respect to foraminifera, and a region that has been has been a focus of the N isotope research of the PI for the last decade and others previously. Moreover, its significant seasonality -- in physical oceanography, biogeochemistry, and foraminiferal species abundance -- will facilitate the effort to understand the controls on fb-del15N at a mechanistic level. The research team will participate in six Bermuda Atlantic Time-series Study (BATS) cruises over two years, collecting foraminifera and other N forms likely to provide insight into the controls on fb-del15N. From the nearby Oceanic Flux Program (OFP) moored sediment traps and from shallow sediments collected in the region, they will pick foraminifera shells and again make relevant ancillary measurements. This work will establish the relationship of foraminiferal biomass to shell-bound del15N for different species, and comparison of the foraminiferal isotope data with the upper ocean N pools will yield empirical isotopic relationships and work toward a mechanistic insight of fb-del15N (e.g., the importance of different N pools to the diets of different foraminifera; the role of algal symbionts). The sediment trap and surface sediment data will support the plankton tow data by integrating over longer time scales and will also address questions regarding late stage (e.g., gametogenic) calcification and the early diagenesis of fb-del15N and fb-N content. Broader Impacts: This study will yield an improved understanding of the nutrient dynamics of foraminifera, a class of organisms whose shells are a central tool in micropaleontology and paleoclimatology. The project will also build on the principal investigator's involvement in the Bermuda Institute of Ocean Sciences as an asset for integrating ocean-related education and research at both the undergraduate and graduate levels.

氮（N）和磷是海洋中浮游植物所需的两种营养素，并且它们共同限制了整个热带，亚热带和温带海洋的生产力。 N及其投入/产出预算的循环都被认为是控制海洋的生育能力和海洋在设定大气CO2中的作用。 有孔虫的CACO3测试可以代表很大一部分海洋沉积物，并已广泛用于古文化。它们是微化石结合有机物的同位素分析的明显靶标。近年来，普林斯顿的研究人员开发了一种方案，用于对有孔虫壳结合N的同位素分析。当前方案的敏感性至少比典型的在线燃烧高100倍，从而可以通过以前不可能测量的N同位素档案快速进步。对表面沉积物的测量和加勒比海的底线记录显示了有孔虫结合的DEL15N（FB-DEL15N）的承诺，既可以为古代摄影提供可靠的N同位素档案，并且具有具有不同深度的多孔物种具有不同深度的生态和行为，并且具有丰富性的独特潜力。 此外，加勒比海记录的发现 - 减少了冰河时代的n固定 - 大西洋的n固定性变化了有关海洋固定N的投入/输出预算的性质的科学对话，以及其改变海洋生育能力和大气二氧化碳的潜力。 然而，对FB-DEL15N的控制尚未进行充分的研究。在该项目中，作为为FB-DEL15N的古文学应用建立基础的第一步，同一普林斯顿大学团队将在水柱中研究其Genesesis在水柱中，运输到海藻和早期的成岩。他们将在百慕大南部的萨尔加索海进行这项研究。这是一般和有孔虫研究的海洋研究区域之一，并且在过去十年和其他其他地区和其他地区一直是PI的N同位素研究的重点。此外，其重要的季节性 - 在物理海洋学，生物地球化学和有孔虫物种的丰度中 - 将有助于在机械水平上理解FB-DEL15N的控制措施。 研究小组将在两年内参加六个百慕大大西洋时间序列研究（BATS）巡航，收集有孔虫和其他N形式，可能会洞悉FB-DEL15N的控制。从附近的海洋通量程序（OFP）系泊沉积物陷阱和该地区收集的浅层沉积物中，它们将挑选有孔虫壳，并再次进行相关的辅助测量。这项工作将建立有孔虫生物量与壳结合的Del15N的关系，用于不同物种，并且有孔虫同位素数据与上海洋n池的比较将产生经验的同位素关系，并致力于FB-DEL15N的机械洞察力（例如，不同n池的重要性与不同的diets a and foraminifera; eminifera; eminiferg; eminiferg; eminiferg;沉积物陷阱和表面沉积物数据将通过整合较长的时间尺度来支持浮游生物牵引数据，还将解决有关晚期（例如配子生成）钙化以及FB-DEL15N和FB-N含量的早期成岩作用的问题。更广泛的影响：这项研究将对有孔虫的营养动力学提高理解，有孔虫是一种生物体，其壳是微石材结构病和古气候学中的核心工具。 该项目还将以主要研究者参与百慕大海洋科学研究所的参与为基础，作为在本科和研究生一级整合与海洋有关的教育和研究的资产。