Collaborative Research: Reconstructing Temperatures during the Mid-Pliocene Warm Period in the McMurdo Dry Valleys with Cosmogenic Noble Gases

合作研究：用宇宙成因惰性气体重建麦克默多干谷中上新世温暖期的温度

• 批准号: 1935945
• 负责人: Marissa Tremblay
• 金额: $ 28.19万
• 依托单位: Purdue University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-08-15 至 2025-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1935945&HistoricalAwards=false
• 关键词: Collaborative; Research; Reconstructing; Temperatures; during

.______________________________________________________________________________________________________________Part I: Nontechnical DescriptionScientists study the Earth's past climate in order to understand how the climate will respond to ongoing global change in the future. One of the best analogs for future climate might the period that occurred approximately 3 million years ago, during an interval known as the mid-Pliocene Warm Period. During this period, the concentration of carbon dioxide in the atmosphere was similar to today's and sea level was 15 or more meters higher, due primarily to warming and consequent ice sheet melting in polar regions. However, the temperatures in polar regions during the mid-Pliocene Warm Period are not well determined, in part because we do not have records like ice cores that extend this far back in time. This project will provide constraints on surface temperatures in Antarctica during the mid-Pliocene Warm Period using a new type of climate substitute, known as cosmogenic noble gas paleothermometry. This project focuses on an area of Antarctica called the McMurdo Dry Valleys. In this area, climate models suggest that temperatures were more than 10 C warmer during the mid-Pliocene than they are today, but indirect geologic observations suggest that temperatures may have been similar to today. The McMurdo Dry Valleys are also a place where rocks have been exposed to Earth surface conditions for several million years, and where this new climate substitute can be readily applied. The team will reconstruct temperatures in the McMurdo Dry Valleys during the mid-Pliocene Warm Period in order to resolve the discrepancy between models and indirect geologic observations and provide much-needed constraints on the sensitivity of Antarctic ice sheets to warming temperatures. The temperature reconstructions generated in this project will have scientific impact in multiple disciplines, including climate science, glaciology, geomorphology, and planetary science. In addition, the project will (1) broaden the participation of underrepresented groups by supporting two early-career female principal investigators, (2) build STEM talent through the education and training of a graduate student, (3) enhance infrastructure for research via publication of a publicly-accessible, open-source code library, and (4) be broadly disseminated via social media, blog posts, publications, and conference presentations.Part II: Technical DescriptionThe mid-Pliocene Warm Period (3-3.3 million years ago) is the most recent interval of the geologic past when atmospheric CO2 concentrations exceeded 400 ppm and is widely considered an analog for how Earth’s climate system will respond to current global change. Climate models predict polar amplification - the occurrence of larger changes in temperatures at high latitudes than the global average due to a radiative forcing - both during the mid-Pliocene Warm Period and due to current climate warming. However, the predicted magnitude of polar amplification is highly uncertain in both cases. The magnitude of polar amplification has important implications for the sensitivity of ice sheets to warming and the contribution of ice sheet melting to sea level change. Proxy-based constraints on polar surface air temperatures during the mid-Pliocene Warm Period are sparse to non-existent. In Antarctica, there is only indirect evidence for the magnitude of warming during this time. This project will provide constraints on surface temperatures in the McMurdo Dry Valleys of Antarctica during the mid-Pliocene Warm Period using a newly developed technique called cosmogenic noble gas (CNG) paleothermometry. CNG paleothermometry utilizes the diffusive behavior of cosmogenic 3He in quartz to quantify the temperatures rocks experience while exposed to cosmic-ray particles within a few meters of the Earth’s surface. The very low erosion rates and subzero temperatures characterizing the McMurdo Dry Valleys make this region uniquely suited for the application of CNG paleothermometry for addressing the question: what temperatures characterized the McMurdo Dry Valleys during the mid-Pliocene Warm Period? To address this question, the team will collect bedrock samples at several locations in the McMurdo Dry Valleys where erosion rates are known to be low enough that cosmic ray exposure extends into the mid-Pliocene or earlier. They will pair cosmogenic 3He measurements, which will record the thermal histories of our samples, with measurements of cosmogenic 10Be, 26Al, and 21Ne, which record samples exposure and erosion histories. We will also make in situ measurements of rock and air temperatures at sample sites in order to quantify the effect of radiative heating and develop a statistical relationship between rock and air temperatures, as well as conduct diffusion experiments to quantify the kinetics of 3He diffusion specific to each sample. This suite of observations will be used to model permissible thermal histories and place constraints on temperatures during the mid-Pliocene Warm Period interval of cosmic-ray exposure.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.

________________________________________________________________________________________________________ 第一部分：非技术描述科学家研究地球过去的气候，以便了解气候将如何应对未来持续的全球变化。未来气候的最佳类比之一可能是大约 300 万年前发生的时期，即上新世中期温暖期。在此期间，大气中二氧化碳的浓度与今天相似，海平面高出 15 米或更多，这主要是由于气候变暖以及随之而来的极地冰盖融化。然而，上新世中期温暖期极地地区的温度还没有得到很好的确定，部分原因是我们没有像冰芯这样可以追溯到这么远的时间的记录。该项目将使用一种新型的气候替代方法（称为宇宙成因惰性气体古温度测量法）对上新世中期温暖期南极洲的表面温度进行限制。该项目重点关注南极洲一个名为麦克默多干谷的地区。气候模型表明，上新世中期该地区的气温比现在高出 10 摄氏度以上，但间接地质观测表明，当时的气温可能与今天相似。麦克默多干谷也是岩石暴露于地球表面条件数百万年的地方，并且可以很容易地应用这种新的气候替代品。该团队将重建上新世中期温暖期麦克默多干谷的温度，以解决模型与间接地质观测之间的差异，并为南极冰盖对气温变暖的敏感性提供急需的约束。该项目中生成的温度重建将对多个学科产生科学影响，包括气候科学、冰川学、地貌学和行星科学。此外，该项目将 (1) 通过支持两名职业生涯早期的女性首席研究员来扩大代表性不足群体的参与，(2) 通过研究生的教育和培训培养 STEM 人才，(3) 通过发布可公开访问的开源代码库来加强研究基础设施，以及 (4) 通过社交媒体、博客文章、出版物和会议演示进行广泛传播。第二部分：技术说明 上新世中期温暖期（距今 3-330 万年）是地质历史上最近的一段时期，当时大气中二氧化碳浓度超过 400 ppm，并且被广泛认为是地球气候系统如何应对当前全球变化的类比。气候模型预测极地放大——由于辐射强迫，高纬度地区的温度变化比全球平均水平更大——无论是在上新世中期温暖期还是由于当前的气候变暖。然而，在这两种情况下，预测的极性放大幅度都高度不确定。极地放大的幅度对于冰盖对变暖的敏感性以及冰盖融化对海平面变化的贡献具有重要意义。上新世中期温暖时期对极地表面气温的基于代理的约束很少甚至不存在。在南极洲，只有间接证据表明这段时间变暖的程度。该项目将使用一种新开发的称为宇宙成因稀有气体（CNG）古测温法的技术，对上新世中期温暖时期南极洲麦克默多干谷的地表温度进行限制。 CNG 古测温法利用石英中宇宙成因 3He 的扩散行为来量化岩石在暴露于地球表面几米范围内的宇宙射线粒子时所经历的温度。麦克默多干谷的极低侵蚀率和零度以下的温度使得该地区非常适合应用 CNG 古测温法来解决以下问题：上新世中期温暖时期麦克默多干谷的特征温度是多少？为了解决这个问题，研究小组将在麦克默多干谷的几个地点收集基岩样本，这些地点的侵蚀率已知足够低，宇宙射线暴露可以延伸到上新世中期或更早。他们将把记录样品热历史的宇宙 3He 测量与记录样品暴露和侵蚀历史的宇宙 10Be、26Al 和 21Ne 测量配对。我们还将对样品地点的岩石和空气温度进行原位测量，以量化辐射加热的影响并建立岩石和空气温度之间的统计关系，并进行扩散实验以量化每个样品特有的 3He 扩散动力学。这套观测结果将用于模拟允许的热历史，并对上新世中期宇宙射线暴露期间的温度施加限制。该奖项反映了 NSF 的法定使命，并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，被认为值得支持。

项目成果

Cosmogenic 3 He paleothermometry on post-LGM glacial bedrock within the central European Alps

中欧阿尔卑斯山内末次盛冰期后冰川基岩的宇宙成因 3 He 古温度测量

• DOI: 10.5194/gchron-4-641-2022
• 发表时间: 2022
• 期刊: Geochronology
• 作者: Gribenski, Natacha;Tremblay, Marissa M.;Valla, Pierre G.;Balco, Greg;Guralnik, Benny;Shuster, David L.
• 通讯作者: Shuster, David L.