When was Summit, Greenland last ice-free: 81Kr dating of dirty ice at the bottom of the GISP2 ice core

格陵兰岛萨米特最后一次无冰是什么时候：GISP2冰芯底部脏冰的81Kr测年

• 批准号: 2052958
• 负责人: Michael Bender
• 金额: $ 13.59万
• 依托单位: Princeton 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: 2021-06-15 至 2024-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2052958&HistoricalAwards=false
• 关键词: When; was; Summit; Greenland; last

Ice sheets melt as Planet Earth becomes warmer. This melting causes sea level to rise, constituting one of the most serious problems resulting from global warming. Complete melting of the Greenland Ice Sheet would raise the average level of the oceans by 7 meters, with significant consequences for cities and towns along the coasts of the world. Understanding how extensively the Greenland Ice Sheet melted in the past will help us predict how fast it will melt in the future. The investigators will determine the age of ice at the very bottom of the ice sheet. The measurements will be made on ice from a site called “GISP2”, in central Greenland, where a hole has been drilled through the 3053-meter thick ice sheet. The ice at the bottom of the hole is likely to be the oldest ice on Greenland and the dating of this bottom ice will tell us the last time that Greenland was not covered by a big ice sheet. By comparing the time when Greenland was ice-free with global climate events that occurred in the past, we hope to learn why the Greenland Ice Sheet melted in the past, and what human activities might cause it to melt in the future. This work will have 2 major benefits to society. First, it will lead to a better understanding of how human activities are likely to affect sea level in the future. Second, it will lead to the training of a postdoctoral fellow, who will collect most of the data, understand the results, and develop research skills that will complete her training as an outstanding independent scientist.The great planetary ice sheets may melt due to global warming, causing sea level to rise. Complete melting of the East Antarctic ice sheet would raise sea level by 53 m, melting of the West Antarctic Ice Sheet would lead to a 5 m rise, and melting of Greenland would cause a 7 m rise. The Greenland ice sheet is generally regarded as most susceptible to melting and therefore of greatest concern. Melting of the Greenland Ice Sheet would lead to a catastrophic rise in sea level, causing flooding of coastal cities as well as lowlands near the ocean. A premise of this proposal is that, if we determine when Greenland was last ice-free, we will have new information which will help us predict the rate of melting in the future, and, consequent rate of sea level rise. The investigators will determine the age of ice at the very bottom of the ice sheet. We will do this using a method called “krypton 81 dating”. Krypton 81 is a form of krypton that is radioactive and gradually changes into another element. The lower the krypton-81 concentration in air trapped in ancient ice, the older the ice. The measurements will be made on ice from a site called “GISP2”, in central Greenland, where a hole has been drilled through the 3053-meter thick ice sheet. The dating measurements will be made at the University of Science and Technology of China, in Hefei. This University has the one instrument in the world capable of measuring the abundance of 81Kr with the required accuracy. Having dated the oldest ice, we will examine the age in the context of known global climate events that occurred around the same time. For example, climate was particularly warm at several times in the past, including 400,000 years ago and 1,070,000 years ago. A date near one of those 2 times would suggest that the planetary warming was sufficient to melt the Greenland Ice Sheet, after which the planet cooled and Greenland was continuously glaciated. This information would challenge global climate models to account for global warming at the appropriate time and would clarify what is required for the melting and regrowth of the ice sheet. This new insight would, in turn, improve our ability to estimate the melting trajectory of the Greenland Ice Sheet on human-relevant timescales (say, thousands to hundreds of thousands of years). It would also improve our ability to understand past climate events and the role of Greenland melting. A Postdoctoral Fellow will be directly responsible for most aspects of the project, including preparing ice core samples for analysis, extracting dissolved gases, interpreting the results, preparing a paper reporting the data, and submitting the results to the NSF Arctic Data Center. The post doctoral scientist will be mentored by the PI and provide support for becoming an independent scientist playing an important role in moving the field forward.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.

随着地球变暖，冰盖融化。这种融化导致海平面上升，这是全球变暖造成的最严重的问题之一。格陵兰冰盖完全融化将使海平面平均上升 7 米，对世界沿海城镇产生重大影响。了解格陵兰冰盖过去融化的范围将帮助我们预测它未来融化的速度。研究人员将确定冰盖最底部冰的年龄。这些测量将在格陵兰岛中部一个名为“GISP2”的地点的冰上进行，该地点已在 3053 米厚的冰盖上钻了一个洞。洞底部的冰很可能是格陵兰岛最古老的冰，对底部冰的测年将告诉我们格陵兰岛最后一次未被大冰盖覆盖的时间。通过将格陵兰岛无冰时期与过去发生的全球气候事件进行比较，我们希望了解格陵兰岛冰盖过去为何融化，以及未来哪些人类活动可能导致其融化。这项工作将为社会带来两大好处。首先，它将有助于更好地了解人类活动可能如何影响未来的海平面。其次，它将培养一名博士后研究员，她将收集大部分数据，了解结果，并发展研究技能，从而完成她作为一名杰出独立科学家的培训。巨大的行星冰盖可能会因全球变暖而融化，导致海平面上升。南极东部冰盖完全融化将使海平面上升53 m，南极西部冰盖融化将导致海平面上升5 m，格陵兰岛融化将导致海平面上升7 m。格陵兰冰盖通常被认为最容易融化，因此最受关注。格陵兰冰盖融化将导致海平面灾难性上升，导致沿海城市和靠近海洋的低地被洪水淹没。该提案的前提是，如果我们确定格陵兰岛上次无冰的时间，我们将获得新的信息，帮助我们预测未来的融化速度，以及随之而来的海平面上升速度。研究人员将确定冰盖最底部冰的年龄。我们将使用一种称为“氪81约会”的方法来做到这一点。氪 81 是氪的一种形式，具有放射性并逐渐转变为另一种元素。古代冰中空气中的氪 81 浓度越低，冰就越古老。这些测量将在格陵兰岛中部一个名为“GISP2”的地点的冰上进行，该地点已在 3053 米厚的冰盖上钻了一个洞。测年工作将在位于合肥的中国科学技术大学进行。该大学拥有世界上唯一一台能够以所需精度测量 81Kr 丰度的仪器。在测定了最古老的冰的年代后，我们将在大约同一时间发生的已知全球气候事件的背景下研究其年龄。例如，过去有几次气候特别温暖，包括40万年前和107万年前。如果日期接近这两个时间之一，则表明地球变暖足以融化格陵兰冰盖，此后地球变冷，格陵兰岛持续冰川化。这些信息将挑战全球气候模型在适当的时间解释全球变暖，并将澄清冰盖融化和再生所需的条件。反过来，这一新见解将提高我们在与人类相关的时间尺度（例如数千到数十万年）内估计格陵兰冰盖融化轨迹的能力。它还将提高我们了解过去的气候事件和格陵兰岛融化的作用的能力。博士后研究员将直接负责该项目的大部分方面，包括准备冰芯样本进行分析、提取溶解气体、解释结果、准备报告数据的论文以及将结果提交给 NSF 北极数据中心。博士后科学家将接受 PI 的指导，并为成为一名独立科学家提供支持，在推动该领域发展方面发挥重要作用。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。