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.

南大洋硅藻化石的化学成分提供了有关南极洲环境历史的信息，包括海冰范围、生物生产和海洋营养物分布。海冰区是一群硅藻的重要栖息地，这些硅藻主要来自角毛藻属，它们在环境压力下具有独特的生命周期阶段，此时它们会产生一种称为休眠孢子的结构。当条件更有利时，休眠孢子会在海洋表面重新播种。这些重的休眠孢子的产生往往会从表面海洋中去除大量的碳和硅，这些必需的营养物质。因此，该小组有可能从表层海洋中去除碳，并可以影响科学家用来重建环境变化的沉积记录。该项目利用这些化石的氮同位素特征探索沉积记录中休眠孢子的作用，以及如何使用这些测量来估计碳循环变化。这项工作将包括对这些生物体进行实验室孵化，以回答静息孢子的化学成分与典型硅藻细胞的化学成分是否以及如何不同。孵化结果将用于评估地球历史上两个对比时期（最后一个冰河时代和温暖的上新世）海冰环境中养分的减少。这项工作应该对科学界如何考虑南大洋季节性海冰覆盖对全球气候的响应和调节影响产生重大影响。该项目为本科生和研究生提供培训和研究机会。南极地球科学领域正在进行的研究工作将通过母机构的交互式展示进行传播。这里提出的工作将解决角毛藻静息孢子如何记录其氮稳定同位素组成中的表面营养条件的不确定性、其特定信号与尊重完整的沉积组合，及其偏置或加强海冰区环境重建的潜力。对实验室中生长的单个物种的硝酸盐、生物量、硅藻结合氮和硅氮比的氮稳定同位素的测量将用于量化静息孢子如何记录水柱中的养分减少及其特征偏向于低营养条件。这些关系将用于为上新世沿海冰湖和跨越末次盛冰期的开放海洋核心的养分减少的硅藻结合氮同位素重建提供信息。该提案利用了南大洋角毛藻属分离株的可用性。 2017 年为拟议的文化工作和存档的沉积物岩芯和/或现有数据收集的数据。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。