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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自《2021年美国救援计划法案》(公法117-2)。大多数海洋生命需要充足的溶解氧供应。海水中的氧浓度受温度、海洋环流和生物活动的影响。所有这些因素都可能随着大气二氧化碳水平的上升而改变。海洋氧气浓度的地质记录可以显示气候变化过去是如何影响海洋氧气浓度的。这一知识将改善对未来海洋氧气水平的预测。自然冰川周期与大气二氧化碳浓度的变化有关。这项研究将重建上一次冰川周期中的海洋氧气水平。这项研究将使用一种新的方法--深海珊瑚中保存的天然铀同位素记录来估计溶解氧。这些珊瑚记录了它们生长时海水的组成。这项研究将分析过去20多万年的珊瑚化石。这些记录将提高对气候和海洋氧气水平之间联系的理解。该项目的更广泛影响包括支持一名博士后研究员和一名研究生。研究小组将与加州理工学院教学、学习和推广中心合作，安排教育和推广活动。这些活动包括参观K-12学校，指导高中暑期研究项目，以及举办公开讲座。这些活动的目标是提高公众对过去和现在气候变化的认识。为了了解海洋氧气水平在冰期-间冰期循环期间的波动，这项工作将把一种新的U同位素(238U/235U)古氧化还原替代物应用于一组独特的深海珊瑚。铀是一种氧化还原敏感元素，其在海洋中的同位素组成(1)主要受全球海底缺氧程度的控制，(2)当碳酸盐没有成岩和碎屑影响时，可以准确地记录在碳酸盐中。这里要研究的深海珊瑚生长在公海海山上的富氧环境中，这意味着当地和/或次级过程不太可能影响它们的铀同位素组成。通过以高时间分辨率表征过去大约200,000年来来自多个地点和深度的保存极为完好的深海珊瑚的238U/235U，将重建详细的海水238U/235U记录。为了解决238U/235U的微小变化，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。为了最有力地解释将要获得的高分辨率和高精度记录，将使用一个新的反同位素质量平衡模型，该模型将允许量化跨冰川-间冰期循环的海底缺氧程度。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。