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: 1935907
• 负责人: Gregory Balco
• 金额: $ 2.97万
• 依托单位: Berkeley Geochronology Center
• 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 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1935907&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.

。在大约300万年前发生的时期，在被称为中新世中期温暖时期的时间间隔时，未来气候的最佳类似物之一可能是发生的时期。在此期间，大气中二氧化碳的浓度与今天的水平相似，海平面高15米或更高，这主要是由于极地区域的变暖和随之而来的冰盖融化。但是，在中新世温暖时期的极性区域的温度并不是很好地确定，部分原因是我们没有像冰芯这样的记录，可以延伸到时间。该项目将使用一种新型的气候替代品（称为宇宙贵族气体热量计）在中新世温暖期间对南极洲的表面温度的限制。该项目侧重于一个称为McMurdo Dry Valleys的南极地区。在该区域，攀登模型表明，在上新世中期的温度比今天的温度高10 c，但间接地质观察表明，温度可能与今天相似。 McMurdo Dry Valleys也是岩石已接触到地面条件已有数百万年的地方，并且可以很容易地使用这种新的气候替代品。该团队将在中新世中期温暖时期重建麦克默多干山谷中的温度，以解决模型和间接地质观察之间的差异，并对南极冰盖对温暖温度的敏感性提供急需的约束。该项目中产生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。 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中新世温暖时期（3-330万年前）是地质过去的最新间隔，当时大气中的二氧化碳浓度超过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模拟。气候模型预测极性扩增 - 高纬度的温度变化比辐射强迫造成的全球平均水平发生较大变化 - 这是在中新世中期温暖时期和当前气候变暖所致。但是，在这两种情况下，极性扩增的预测幅度都高度不确定。极性扩增的大小对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。在中新世中期温暖期间，基于代理对极性表面空气温度的约束稀疏到不存在。在南极，只有间接证据表明在这段时间内变暖的程度。该项目将使用一种新开发的技术，称为宇宙基因贵族气体（CNG）苍白的效果测定法。 CNG的淡淡热度计利用石英中宇宙基因的差异行为来量化岩石体验，同时暴露于地球表面几米之内的宇宙射线颗粒。麦克穆尔多干山谷的表征非常低的侵蚀速率和亚零温度使该区域独特地适合应用CNG的佩弗热量法来解决以下问题：哪些温度是在中新世温暖的期间中麦克穆尔多（McMurdo）干山谷的特征？为了解决这个问题，该团队将在麦克穆尔多干谷的多个位置收集基岩样品，众所周知，侵蚀速率足够低，以至于宇宙射线暴露延伸到中新世中期或更早。他们将将宇宙源性3HE测量与宇宙基因10BE，26AL和21NE的测量结果相结合，该测量记录了我们的样品的热历史，并记录了样品的暴露和侵蚀历史。我们还将在样品位点对岩石和空气温度进行原位测量，以量化辐射加热并在岩石与空气温度之间发展统计关系的影响，以及进行扩散实验，以量化每个样品特定的3HE差异的动力学。这套观察套件将用于建模许可热历史，并在宇宙射线曝光的中新世温暖期间间隔内对温度的限制。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和更广泛影响的审查标准来通过评估来通过评估来获得的支持。