Collaborative Proposal: A Field and Laboratory Examination of the Diatom N and Si Isotope Proxies: Implications for Assessing the Southern Ocean Biological Pump

合作提案：硅藻 N 和 Si 同位素代理的现场和实验室检查：对评估南大洋生物泵的影响

• 批准号: 1341464
• 负责人: Rebecca Robinson
• 金额: $ 41.36万
• 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: 2016
• 资助国家: 美国
• 起止时间: 2016-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1341464&HistoricalAwards=false
• 关键词: Collaborative; Proposal; Field; Laboratory; Examination

Collaborative Proposal: A field and laboratory examination of the diatom N and Si isotope proxies: Implications for assessing the Southern Ocean biological pumpThe rise in atmospheric carbon dioxide concentrations and associated climate changes make understanding the role of the ocean in large scale carbon cycle a priority. Geologic samples allow exploration of potential mechanisms for carbon dioxide drawdown during glacial periods through the use of geochemical proxies. Nitrogen and silicon isotope signatures from fossil diatoms (microscopic plants) are used to investigate changes in the physical supply and biological demand for nutrients (like nitrogen and silicon and carbon) in the Southern Ocean. The project will evaluate the use the nitrogen and silicon isotope proxies through a series of laboratory experiments and Southern Ocean field sampling. The results will provide quantification of real relationships between nitrogen and silicon isotopes and nutrient usage in the Southern Ocean and allow exploration of the role of other factors, including biological diversity, ice cover, and mixing, in altering the chemical signatures recorded by diatoms. Seafloor sediment samples will be used to evaluate how well the signal created in the water column is recorded by fossil diatoms buried in the seafloor. Improving the nutrient isotope proxies will allow for a more quantitative understanding of the role of polar biology in regulating natural variation in atmospheric carbon dioxide. The project will also result in the training of a graduate student and development of outreach materials targeting a broad popular audience.This project seeks to test the fidelity of the diatom nitrogen and silicon isotope proxies, two commonly used paleoceanographic tools for investigating the role of the Southern Ocean biological pump in regulating atmospheric CO2 concentrations on glacial-interglacial timescales. Existing ground-truthing data, including culture experiments, surface sediment data and downcore reconstructions, all suggest that nutrient utilization is the primary driver of isotopic variation in the Southern Ocean. However, strong contribution of interspecific variation is implied by recent culture results. Moreover, field and laboratory studies present some contradictory results in terms of the relative importance of interspecific variation and of inferred post-depositional alteration of the nutrient isotope signals. Here, a first order test of the N and Si diatom nutrient isotope paleo-proxies, involving water column dissolved and particulate sampling and laboratory culturing of field-isolates, is proposed. Southern Ocean water, biomass, live diatoms and fossil diatom sampling will be conducted to investigate species and assemblage related variability in diatom nitrogen and silicon isotopes and their relationship to surface nutrient fields and early diagenesis. Access to fresh materials produced in an analogous environmental context to the sediments of primary interest is critical for making robust paleoceanographic reconstructions. Field sampling will occur along 175°W, transecting the Antarctic Circumpolar Current from the subtropics to the marginal ice edge. Collection of water, sinking/suspended particles and multi-core samples from 13 stations and 3 shipboard incubation experiments will be used to test four proposed hypotheses that together evaluate the significance of existing culture results and seek to allow the best use of diatom nutrient isotope proxies in evaluating the biological pump.

协作提案：硅藻N和SI同位素代理的现场和实验室检查：评估南方海洋生物泵的影响，大气二氧化碳浓度的上升以及相关的气候变化使人们了解海洋在大规模碳循环中的作用。地质样品允许通过使用地球化学代理来探索冰川时期二氧化碳减量的潜在机制。化石硅藻（微观植物）的氮和硅同位素特征用于研究南大洋中营养素（例如氮，硅和碳）物理供应和生物学需求的变化。该项目将通过一系列实验室实验和南方海洋田间采样来评估氮和硅同位素代理的使用。该结果将提供量化氮与硅同位素之间的实际关系以及南大洋中的营养用法，并允许探索其他因素的作用，包括生物多样性，冰盖和混合，改变硅藻记录的化学特征。海底沉积物样品将用于评估水柱中所产生的信号的记录，化石硅藻在海底内建造的信号。改善养分同位素代理将使对极性生物学在确定大气二氧化碳自然变化中的作用的作用有更定量的理解。该项目还将导致培训研究生，并针对广泛受众的外展材料的发展。该项目旨在测试硅藻氮和硅同位素代理的忠诚度，这是两种通常使用的古疗法工具，用于调查南方海洋生物泵在调节大气中浓度熟悉熟悉熟料的熟料时代的作用。现有的地面研究数据，包括培养实验，表面沉积物数据和下侧重建，所有这些都表明营养利用率是南大洋同位素变化的主要驱动力。但是，最近培养结果暗示了种间变异的强烈贡献。此外，野外和实验室研究就种间变异和推断的营养同位素信号的指定后沉积变化的相对重要性提出了一些矛盾的结果。在这里提出了N和Si Diotom养分同位素古质子的一阶测试，该测试涉及水柱溶解和特定的采样和实验室培养物的野外溶质培养物。将进行南部海水，生物量，活硅藻和化石硅藻采样，以研究硅氮和硅同位素的物种和组合相关的变异性及其与表面养分场和早期成岩作用的关系。在类似的环境环境中与主要兴趣沉积物相似的新鲜材料的访问对于制造强大的古质学重建至关重要。场采样将沿175°W进行，将南极圆极电流从亚热带到边缘冰边缘。从13个站点收集了水，下沉/悬浮颗粒和多核样品，以及3个船舶孵化实验将用于测试四个提出的假设，共同评估现有培养结果的重要性，并寻求允许在评估生物泵方面充分利用硅藻同位素的同位素代理。