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

.______________________________________________________________________________________________________________Part I：非技术描述科学家研究地球S回顾了气候，以便了解未来气候将如何应对正在进行的全球变化。对未来气候最好的类比之一可能是大约300万年前的时期，那段时间被称为上新世中期暖期。在此期间，大气中的二氧化碳浓度与今天相似，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，上新世中期暖期极地地区的温度并没有得到很好的确定，部分原因是我们没有像冰芯这样的记录可以追溯到很久以前。该项目将使用一种新型的气候替代品，即宇宙成因惰性气体古温度计，来限制上新世中期南极洲表面的温度。该项目的重点是南极洲一片名为麦克默多干谷的区域。在这一地区，气候模型表明，上新世中期的温度比现在高出10摄氏度以上，但间接的地质观察表明，温度可能与今天相似。麦克默多干燥山谷也是岩石暴露在地球表面条件下数百万年的地方，这种新的气候替代品可以很容易地应用。该团队将重建麦克默多干燥山谷在上新世中期暖期的温度，以解决模型和间接地质观测之间的差异，并对南极冰盖对气温变暖的敏感性提供亟需的限制。该项目产生的温度重建将在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初期的女性首席调查员扩大代表不足群体的参与，(2)通过教育和培训一名研究生培养STEM人才，(3)通过出版可供公众查阅的开放源码资料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、第二部分：技术描述上新世中期暖期(300-330万年前)是过去地质历史中大气二氧化碳浓度超过400ppm的最新时段，被广泛认为是地球气候系统将如何应对当前全球变化的类比。气候模型预测了极地放大--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是高度不确定的。极地放大的大小对冰盖对气候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。上新世中期暖期极地表面气温的代理约束很少，甚至根本不存在。在南极洲，只有间接证据表明在这段时间内气候变暖的幅度。该项目将使用一种名为宇宙成因惰性气体(CNG)古测温的新技术，对上新世中期南极洲麦克默多干燥山谷的表面温度进行限制。CNG古测温仪利用宇宙成因的3He在石英中的扩散行为来量化岩石在地球表面几米内暴露于宇宙射线粒子时所经历的温度。麦克默多干河谷具有极低的侵蚀速率和零下的温度，这使得该地区特别适合应用CNG古温度计来解决以下问题：麦克默多干河谷在上新世中期暖期的特点是什么温度？为了解决这个问题，该团队将在麦克默多干燥山谷的几个地点收集基岩样本，这些地点的侵蚀速度已知足够低，以至于宇宙射线暴露到上新世中期或更早。他们将把记录我们样品热历史的宇宙成因3He测量与记录样品暴露和侵蚀历史的宇宙成因10Be、26Al和21Ne测量配对。我们亦会在样本现场量度岩石和空气温度，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，以及进行扩散实验，以量化每个样本的3He扩散动力学。这套观测结果将用于模拟允许的热历史，并对宇宙射线暴露的中上新世暖期期间的温度施加限制。这一奖项反映了美国国家科学基金会的法定使命，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。

.______________________________________________________________________________________________________________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.