Collaborative Research: Illuminating the Cenozoic Alkenone pCO2 Record

合作研究：阐明新生代烯酮 pCO2 记录

• 批准号: 2100537
• 负责人: Ann Pearson
• 金额: $ 38.43万
• 依托单位: Harvard University
• 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=2100537&HistoricalAwards=false
• 关键词: Collaborative; Research; Illuminating; Cenozoic; Alkenone; Collaborative; Research; Illuminating; Cenozoic; Alkenone

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). This study will improve the foundation of a widely used geologic proxy for atmospheric carbon dioxide. To correctly predict the magnitude of future global warming from rising greenhouse gas (GHG) concentrations, it is essential to understand the relationship between GHGs – particularly carbon dioxide (CO2) – and Earth’s temperature. One way to investigate this relationship is to examine how Earth’s temperature and CO2 levels have varied together in the past. Direct measurements of atmospheric CO2 extend back only to 1958, while measurements from bubbles of atmosphere trapped in ice cores extend back to about 1 million years (Ma) ago. Any estimate of CO2 older than about 1 Ma requires the use of a proxy for CO2 concentrations. One such proxy is based upon how ‘picky’ marine algae are about the two different isotopes of carbon. When algae grow with high CO2 levels they mostly take up the isotope carbon-12, and use less of the isotope carbon-13. When they grow with low CO2 levels they take up relatively more carbon-13. However, recent findings show that marine algae may also change how ‘picky’ they are due to other factors besides CO2 levels. The primary goal of this project is to investigate how these other factors affect the algal CO2 proxy through controlled laboratory experiments and analysis of modern ocean sediments. These findings can then be applied to ancient ocean sediments, in order to improve interpretations of reconstructed CO2 levels in the past. This project will train a post-doctoral investigator, a Ph.D. student, and two summer undergraduate interns.Accurate reconstructions of past atmospheric pCO2 levels can improve predictions of future warming by providing geologic tests during Earth conditions that were different from the short observational record. An important proxy for CO2 concentrations during the past 55 million years is the carbon isotopic composition of long-chain unsaturated ketones (alkenones) from the Noelaerhabdaceae family of algae. The crucial assumptions of the existing proxy are that: (i) carbon isotope fractionation (Ep) by these algae is set by the rate of diffusive supply of CO2 relative to the rate of carbon use, and (ii) the fractionation is primarily governed by the carbon-fixing enzyme RuBisCO, with an assumed isotope effect of roughly 25 per mil. Recent work challenges these assumptions, suggesting that non-diffusive supply of CO2 is ubiquitous, that kinetic RuBisCO fractionation in these algae may be as small as about 11 per mil and that irradiance independently influences carbon isotope fractionation. Additional information is needed to incorporate these new factors into quantitative reconstructions of pCO2, including re-interpreting Cenozoic alkenone Ep values. Project objectives include:i. Measure the response of alkenone Ep to variations in irradiance, cell size, and pCO2 in laboratory chemostat and dilute batch cultures,ii. Revise the quantitative framework for alkenone paleobarometry, developing practical equations to use for paleo-pCO2 reconstruction, andiii. Test this revised laboratory-based framework with new sediment analyses from the modern and Pleistocene ocean.The project goal is to provide a framework, based in mechanistic rather than empirical evidence, for understanding alkenone Ep variations during the Cenozoic. This will help develop an equation relating Ep to CO2 that uses variables that can be measured or easily estimated, and that could be adopted readily by the paleoclimate community.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.

该奖项是根据2021年《美国救援计划法》（公法117-2）全部或部分资助的。这项研究将改善广泛使用大气二氧化碳的地质代理的基础。为了正确预测温室气体（GHG）浓度的未来全球变暖的大小，必须了解温室气体（尤其是二氧化碳（CO2））与地球温度之间的关系。研究这种关系的一种方法是检查地球的温度和二氧化碳水平在过去如何变化。大气二氧化碳的直接测量只能追溯到1958年，而被困在冰块中的大气气泡的测量值延伸到大约100万年（MA）。大于1 MA的二氧化碳的任何估计都需要使用代理二氧化碳浓度。这样的代理是基于“挑剔”海洋藻类对碳的两个不同同位素的方式。当藻类以高二氧化碳水平生长时，它们主要占用同位素碳12，并且使用较少的同位素碳-13。当它们以低二氧化碳水平生长时，它们占相对较高的碳13。但是，最近的发现表明，海洋藻类还可能改变它们除了二氧化碳水平以外的其他因素所致。该项目的主要目标是通过受控实验室实验和现代海洋沉积物的分析来研究这些其他因素如何影响藻类CO2的代理。然后，这些发现可以应用于古老的海洋沉积物，以改善过去重建的二氧化碳水平的解释。该项目将培训博士后研究员博士学位。学生和两个夏季的本科生杂志。过去的大气PCO2水平的重建可以通过在地球条件下提供与短期观察记录不同的地球条件下的地质测试来改善对未来变暖的预测。在过去的5500万年中，二氧化碳浓度的重要代理是藻类Noelaeraerhabdaceae家族的长链不饱和酮（烯烃）的碳同位素组成。现有代理的关键假设是：（i）这些藻类的碳同位素分馏（EP）是由相对于碳使用率不同的二氧化碳供应速率而设置的，并且（ii）分馏主要由碳固定酶Rubisco控制，并由假定的同位素效应（每平均25毫米）构成了高度25毫米。最近的工作对这些假设提出了挑战，表明二氧化碳的供应无处不在，这些藻类的动力学rubisco分馏可能高达每mil 11，并且辐照度独立影响碳同位素分馏。需要其他信息将这些新因素纳入PCO2的定量重建中，包括重新解释新生代烯酮EP值。项目对象包括：i。测量实验室化学仪和稀释批量培养物中烯酮EP对辐照度，细胞大小和PCO2变化的反应，ii。修改烯酮古生物计量学的定量框架，开发用于古PCO2重建的实用方程，Andiii。通过现代和更新世海洋的新沉积物分析测试该修订的基于实验室的框架。项目目标是提供一个基于机械性的，而不是经验证据的框架，以理解新生代期间烯酮EP的变化。这将有助于开发一个与CO2相关的方程式，该方程使用可以测量或易于估算的变量，并且可以轻松地被古气候社区采用。该奖项反映了NSF的法定任务，并被认为是通过基金会的知识分子优点和更广泛的审查标准通过评估来通过评估来支持的。