Quantifying biological, diagenetic and global redox effects on uranium “stable” isotopes in deep-sea corals across glacial-interglacial cycles

量化冰期-间冰期循环中深海珊瑚中铀“稳定”同位素的生物、成岩和全球氧化还原效应

基本信息

批准号：
2054892
负责人：
Francois Tissot
金额：
$ 48.23万
依托单位：
California Institute of Technology
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2021
资助国家：
美国
起止时间：
2021-08-01 至 2024-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=2054892&HistoricalAwards=false
关键词：
Quantifying biological diagenetic global redox

项目摘要

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Most life in the ocean requires an adequate supply of dissolved oxygen. The oxygen concentration of seawater is impacted by temperature, ocean circulation, and biological activity. All of these factors may change in response to rising atmospheric carbon dioxide levels. Geologic records of ocean oxygen concentration can show how changing climate has influenced marine oxygen concentrations in the past. That knowledge will improve predictions of ocean oxygen levels in the future. Natural glacial cycles are linked to changes in atmospheric carbon dioxide concentrations. This study will reconstruct marine oxygen levels across the last glacial cycle. The study will estimate dissolved oxygen using a new method - records of natural uranium isotopes preserved in deep-sea corals. These corals record the composition of seawater at the time of their growth. The study will analyze fossil corals spanning the last more than 200,000 years. These records will improve understanding of the links between climate and ocean oxygen levels. The Broader Impacts of the project include support for a postdoctoral researcher and a graduate student. The research team will work with the Caltech Center for Teaching, Learning & Outreach to arrange education and outreach activities. Those activities include visits to K-12 schools, mentoring of high-school summer research projects, and hosting of public lectures. The goal of these activities is to increase public awareness of past and current climate change. To understand how ocean oxygen levels have fluctuated during glacial-interglacial cycles, this work will apply a new U isotope (238U/235U) paleo-redox proxy to a unique collection of deep-sea corals. Uranium is a redox-sensitive element whose isotopic composition in the ocean (i) is predominantly controlled by the global extent of seafloor anoxia, and (ii) can be faithfully recorded in carbonates when they are devoid of diagenetic and detrital influences. The deep-sea corals to be studied here grew in oxygenated environments on seamounts in the open ocean, meaning that local and/or secondary processes are unlikely to have impacted their U isotopic composition. By characterizing, at high temporal resolution, the 238U/235U of these exceptionally well-preserved deep-sea corals from multiple sites and depths over the last approximately 200,000 years, a detailed seawater 238U/235U record will be reconstructed. To resolve even subtle variations in 238U/235U, state-of-the-art methods achieving precision and accuracy of ±0.01-0.03‰ on 238U/235U data will be employed. To most robustly interpret the high-resolution and high-precision record to be acquired, a novel inverse isotope mass balance model will be used, which will allow quantification of the extent of seafloor anoxia across glacial-interglacial cycles.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.

该奖项的全部或部分资金来源于《2021 年美国救援计划法案》（公法 117-2）。海洋中的大多数生命都需要充足的溶解氧供应。海水中的氧气浓度受到温度、海洋环流的影响。所有这些因素都可能随着大气二氧化碳浓度的上升而发生变化。海洋氧气浓度的地质记录可以显示气候变化如何影响过去的海洋氧气浓度。未来。冰川周期与大气二氧化碳浓度的变化有关。这项研究将使用一种新方法（深海珊瑚中保存的天然铀同位素记录）来重建海洋氧气水平。该研究将分析过去 20 万年的珊瑚化石，从而加深对气候与海洋含氧量之间关系的了解。该项目的主要内容包括为一名博士后研究员和一名研究生提供支持，该研究团队将与加州理工学院的教学、学习和外展中心合作，安排教育和外展活动，包括参观 K-12 学校、指导高中生。学校暑期研究项目和举办公开讲座的目的是提高公众对过去和当前气候变化的认识，这项工作将应用一种新的U同位素，以了解冰期-间冰期循环期间海洋氧气水平的波动。 (238U/235U) 深海珊瑚的独特集合的古氧化还原代理铀是一种氧化还原敏感元素，其在海洋中的同位素组成 (i) 主要受全球海底缺氧程度控制，并且 (ii)当没有成岩和碎屑影响时，可以在碳酸盐中忠实地记录这里要研究的深海珊瑚生长在公海海山的含氧环境中，通过以高时间分辨率表征过去约 200,000 个地点和深度的这些保存异常完好的深海珊瑚的 238U/235U，这意味着局部和/或次生过程不太可能影响其 U 同位素组成。几年后，将重建详细的海水 238U/235U 记录，以解决 238U/235U 的细微变化，将采用最先进的方法，在 238U/235U 数据上实现 ±0.01-0.03‰ 的精度和准确度，为了最有力地解释要获取的高分辨率和高精度记录，将采用一种新颖的反同位素质量平衡。将使用模型，这将允许量化跨冰期-间冰期循环的海底缺氧程度。该奖项反映了 NSF 的法定使命，并被认为值得支持通过使用基金会的智力优点和更广泛的影响审查标准进行评估。