Tracing Past Methane Variations with Stable Isotopes in Antarctic Ice Cores

该项目将开发方法来测量被困在冰芯中的空气中甲烷中碳-13与碳-12的比率，以及重氢与轻氢的比率。不同形式的碳和氢的比例是过去这种气体的不同来源的“指纹”--例如热带湿地和冻结在海底的甲烷。一旦分析方法被开发出来，这些测量将被用来研究甲烷为什么在过去的冰河时期和之前的暖期突然变化。这些数据将被用来了解野火、甲烷水合物和湿地等甲烷来源如何应对气候变化。这些信息是理解随着地球变暖，大气中甲烷发生重大变化的未来风险所必需的。该项目涉及两项任务。首先，研究人员将使用连续流动方法建造和测试甲烷同位素测量的气体提取系统，目标是达到或提高少数几个进行这些测量的其他实验室所达到的精度。该系统将与俄勒冈州立大学现有的质谱仪连接。该系统由真空室和一系列捕集器、净化柱和炉子组成，这些设备将甲烷从其他气体中分离出来，并将其转化为二氧化碳或氢气用于质谱分析。其次，该团队将测量甲烷的同位素组成，包括与过去两个间冰期相关的浓度大幅变化，以及上一个冰期甲烷的突然变化。这些测量将被用来了解这些浓度变化的主要原因是否是气候驱动的湿地排放变化，或者是否涉及其他来源，例如甲烷水合物或野火。这一裁决反映了NSF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。

This project will develop methods to measure the ratios of carbon-13 to carbon-12, and heavy to light hydrogen in methane in air trapped in ice cores. The ratios of the different forms of carbon and hydrogen are "fingerprints" of different sources of this gas in the past--for example wetlands in the tropics versus methane frozen in the sea floor. Once the analysis method is developed, the measurements will be used to examine why methane changed abruptly in the past, both during the last ice age, and during previous warm periods. The data will be used to understand how methane sources like wildfires, methane hydrates, and wetlands respond to climate change. This information is needed to understand future risks of large changes in methane in the atmosphere as Earth warms. The project involves two tasks. First, the investigators will build and test a gas extraction system for methane isotopic measurements using continuous flow methods, with the goal of equaling or bettering the precision attained by the few other laboratories that make these measurements. The system will be interfaced with existing mass spectrometers at Oregon State University. The system consists of a vacuum chamber and sequence of traps, purification columns, and furnaces that separate methane from other gases and convert it to carbon dioxide or hydrogen for mass spectrometry. Second, the team will measure the isotopic composition of methane across large changes in concentration associated with two past interglacial periods and during abrupt methane changes of the last ice age. These measurements will be used to understand if the main reason for these concentration changes is climate-driven changes in emissions from wetlands, or whether other sources are involved, for example methane hydrates or wildfires.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.