The Nitrogen Isotopic Composition of Diatom Resting Spores in Southern Ocean Sediments: A Source of Bias and/or Paleoenvironmental Information?

南大洋沉积物中硅藻休眠孢子的氮同位素组成：偏差和/或古环境信息的来源？

• 批准号: 1744871
• 负责人: Rebecca Robinson
• 金额: $ 39.68万
• 依托单位: University of Rhode Island
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-15 至 2023-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1744871&HistoricalAwards=false
• 关键词: Nitrogen; Isotopic; Composition; Diatom; Resting

The chemical composition of diatom fossils in the Southern Ocean provides information about the environmental history of Antarctica, including sea ice extent, biological production, and ocean nutrient distribution. The sea ice zone is an important habitat for a group of diatoms, largely from the genus Chaetoceros, that have a unique life cycle stage under environmental stress, when they produce a structure called a resting spore. Resting spores are meant to reseed the surface ocean when conditions are more favorable. The production of these heavy resting spores tends to remove significant amounts of carbon and silicon, essential nutrients, out of the surface ocean. As a result, this group has the potential to remove carbon from the surface ocean and can impact the sedimentary record scientists use to reconstruct environmental change. This project explores the role of resting spores in the sedimentary record using the nitrogen isotopic signature of these fossils and how those measurements are used to estimate carbon cycle changes. The work will include laboratory incubations of these organisms to answer if and how the chemistry of the resting spores differs from that of a typical diatom cell. The incubation results will be used to evaluate nutrient drawdown in sea ice environments during two contrasting intervals in earth history, the last ice age and the warm Pliocene. This work should have significant impact on how the scientific community considers the impact of seasonal sea ice cover in the Southern Ocean in terms of how it responds to and regulates global climate. The project provides training and research opportunities for undergraduate and graduate students. Ongoing research efforts in Antarctic earth sciences will be disseminated through an interactive display at the home institution.The work proposed here will address uncertainties in how Chaetoceros resting spores record surface nutrient conditions in their nitrogen stable isotopic composition, the relative impact of their specific signal with respect to the full sedimentary assemblage, and their potential to bias or enhance environmental reconstructions in the sea ice zone. Measurements of nitrogen stable isotopes of nitrate, biomass, and diatom-bound nitrogen and silicon-to-nitrogen ratios of individual species grown in the laboratory will be used to quantify how resting spores record nutrient drawdown in the water column and to what degree their signature is biased toward low nutrient conditions. These relationships will be used to inform diatom-bound nitrogen isotope reconstructions of nutrient drawdown from a Pliocene coastal polyna and an open ocean core that spans the last glacial maximum. This proposal capitalizes on the availability of Southern Ocean isolates of Chaetoceros spp. collected in 2017 for the proposed culture work and archived sediment cores and/or existing data.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.

南大洋中硅藻化石的化学成分提供了有关南极环境历史的信息，包括海冰范围，生物生产和海洋养分分布。海冰区是一组硅藻的重要栖息地，主要来自Chaetoceros属，它们在环境压力下具有独特的生命周期阶段，当时它们会产生一种称为静止孢子的结构。静止的孢子是在条件更有利的情况下播种地面海洋。这些沉重的休息孢子的产生倾向于从地表海洋中清除大量的碳和硅（必需营养素）。结果，该群体有可能从地面海洋中去除碳，并可能影响记录科学家用来重建环境变化。该项目使用这些化石的氮同位素特征以及如何使用这些测量值来估算碳循环变化，探索静息孢子在沉积记录中的作用。这项工作将包括对这些生物的实验室孵育，以回答静息孢子的化学是否以及与典型的硅藻细胞的化学不同。在地球历史上的两个对比间隔，最后一个冰河时代和温暖的上新世，孵化结果将用于评估海冰环境中的养分缩水。这项工作应该对科学界如何考虑季节性海冰覆盖在南大洋的影响方面的影响以及调节全球气候的影响。该项目为本科生和研究生提供了培训和研究机会。南极地球科学的正在进行的研究工作将通过家庭机构的互动式展示来散布。此处提出的工作将解决Chaetoceros静止孢子如何在其氮稳定的同位素组合中记录表面营养条件的不确定性。测量实验室中生长的个别物种的硝酸盐，生物量和硅藻结合的氮和硅与氮的测量将用于量化静息孢子记录水柱中的养分累积累积，并如何降低其标志的偏见，偏向于低营养条件。这些关系将用于告知从上新世沿海Polyna和跨越最后冰川最大值的开放式海洋核心的营养降低的硅藻同位素重建。该提案资本利用了Chaetoceros spp的南洋分离株的可用性。该奖项于2017年收集了2017年的文化工作和归档的沉积物核心和/或现有数据。该奖项反映了NSF的法定任务，并使用基金会的知识分子优点和更广泛的影响审查标准，被认为值得通过评估来获得支持。