Investigation of Past Atmospheric Methane Variability with Stable Isotopes in Antarctic Ice Cores

用南极冰芯稳定同位素研究过去大气甲烷变化

• 批准号: 2324307
• 负责人: Edward Brook
• 金额: $ 53.24万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-10-01 至 2026-09-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2324307&HistoricalAwards=false
• 关键词: Investigation; Past; Atmospheric; Methane; Variability

Atmospheric methane contributes to the greenhouse effect and therefore Earth’s temperature. Humans have caused an almost three-fold increase in methane since the industrial revolution. As the planet warms, changes on the Earth surface and in the atmosphere will further change methane levels. How these feedbacks will change over time is not well known. Studies of past variations in methane, by measuring ancient air trapped in ice, provide examples of these changes and help build better predictions of future change. In this project researchers will use measurements of different chemical forms of the carbon and hydrogen in methane to better understand reasons for past changes. The proposed research will develop laboratory measurement methods for hydrogen isotopes, use the different chemical forms of methane to understand the changes in atmospheric methane that happened when past ice ages ended and the Earth warmed, and use unique, very old ice samples ( 1 million years) from Antarctica to understand what controls methane levels in the atmosphere when climate was as warm or warmer than today. Developing new methods involves testing an existing system for purifying methane for measurements of hydrogen isotopes by mass spectrometry. The system is already operational and calibrated for carbon isotopes in methane. Next, the researchers will measure hydrogen isotopes in methane from samples from Taylor Glacier and Allan Hills, Antarctica, that cover two transitions from ice ages to interglacial warm periods. These data will be used to constrain where the methane increase that happened at these times originated, because hydrogen isotope ratios are sensitive to the latitude of the methane source. Finally, the researchers will measure both carbon and hydrogen isotopes in samples from 1 to 3 million years in age from the Allan Hills Blue Ice Area in Antarctica. Comparisons between these measurements and existing data for younger samples may reveal important differences between the mixture of source types that make up the methane budget in these different time periods. For example, prior to 1 million years ago, the apparent lack of large Northern Hemisphere ice sheets during glacial periods, and resulting higher glacial sea levels, would have had impacts on the global wetland methane source. Additionally, warmer temperatures might have increased CH4 emissions from wetlands but also increased production of the hydroxyl radical and methane destruction in the stratosphere. The project will support a post-doctoral researcher who will collaborate with the Ice Drilling Program at Dartmouth College to create virtual field labs used in high school and college classes.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.

大气中的甲烷会导致温室效应，进而影响地球温度。自工业革命以来，人类造成的甲烷排放量几乎增加了三倍。随着地球变暖，地球表面和大气的变化将进一步改变甲烷水平。这些反馈将如何随着时间的推移而改变尚不清楚。通过测量古代冰中的空气来研究甲烷过去的变化，提供这些变化的例子，并有助于更好地预测未来的变化。在该项目中，研究人员将利用对甲烷中碳和氢不同化学形式的测量来更好地了解过去变化的原因。拟议的研究将开发氢同位素的实验室测量方法，利用甲烷的不同化学形式来了解过去冰河时代结束和地球变暖时大气中甲烷发生的变化，并利用来自南极洲的独特、非常古老的冰样本（100万年）来了解当气候与今天一样温暖或比现在更温暖时，是什么控制着大气中的甲烷水平。开发新方法涉及测试现有的甲烷纯化系统，以通过质谱法测量氢同位素。该系统已经投入运行并针对甲烷中的碳同位素进行了校准。接下来，研究人员将测量南极洲泰勒冰川和艾伦山样本中甲烷中的氢同位素，这些样本涵盖了从冰河时代到间冰期温暖期的两个转变。这些数据将用于限制在这些时间发生的甲烷增加的起源，因为氢同位素比对甲烷源的纬度很敏感。最后，研究人员将测量来自南极洲艾伦山蓝冰区的 1 至 300 万年前样本中的碳同位素和氢同位素。这些测量结果与较年轻样本的现有数据之间的比较可能会揭示在这些不同时间段内构成甲烷预算的源类型混合物之间的重要差异。例如，在100万年前，冰川时期北半球明显缺乏大型冰盖，并导致冰川海平面升高，这会对全球湿地甲烷来源产生影响。此外，气温升高可能会增加湿地的甲烷排放量，但也会增加平流层中羟基自由基的产生和甲烷的破坏。该项目将支持一名博士后研究员，他将与达特茅斯学院的冰钻项目合作，创建用于高中和大学课程的虚拟现场实验室。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。