Atmospheric H2 in the Northern Hemisphere over the past Millennium

该项目将分析格陵兰岛Summit冰芯中的分子氢（H2），以重建过去一千年大气中H2的变化。这将是第一次记录工业时代开始前的过去大气H2。研究结果将揭示古大气H2的自然变率及其与气候变化的关系。由此产生的数据将为评估自前工业化时代以来人类活动如何影响大气H2提供基线。这项研究的结果将为全球评估未来氢经济将如何影响大气成分和气候提供信息。该项目将为博士后学者和本科生提供培训。这项研究包括在顶峰钻探一个新的冰芯，从野外样品中提取空气，随后分析H2、Ne和CH4。根据观测到的H2/Ne比值，可以推断出古大气中H2的含量，以解释在空气捕获过程中孔隙封闭分馏和钻井/采样过程中可能的气体损失。本研究将生成H2的第一个千年尺度大气历史，并研究与中世纪气候异常和小冰期相关的百年尺度变率。预计氢气中与气候相关的变异，因为主要的损失机制是土壤中的微生物吸收，这一过程对水文条件高度敏感。因此，峰会的古大气H2记录将为我们对全球H2生物地球化学循环的理解提供新的约束，并为用于评估未来H2排放的气候敏感性的全球模型提供重要测试。该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知识价值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 analyze molecular hydrogen (H2) in an ice core from Summit, Greenland to reconstruct atmospheric changes in H2 over the past millennium. This will be the first record of past atmospheric H2 prior to the onset of the industrial era. The results will reveal the natural variability in paleo-atmospheric H2 and how it relates to climate change. The resulting data will provide a baseline for assessing how human activities have influenced atmospheric H2 since the preindustrial era. The results of this study will inform global assessments of how the future hydrogen economy will affect atmospheric composition and climate. The project will provide training for a postdoctoral scholar and undergraduate students.The research involves drilling a new ice core at Summit, extracting air from the samples in the field, with subsequent analysis for H2, Ne, and CH4. Paleo-atmospheric levels of H2 will be inferred from the observed H2/Ne ratio to account for pore close-off fractionation during firn air entrapment and possible gas loss during drilling/sampling. This study will generate the first millennial scale atmospheric history of H2 and examine centennial scale variability associated with the Medieval Climate Anomaly and Little Ice Age. Climate-related variability in H2 is expected because the major loss mechanism is microbial uptake in soil, a process that is highly sensitive to hydrological conditions. The Summit paleo-atmospheric H2 record will therefore provide new constraints on our understanding of the global biogeochemical cycling of H2 and an important test for global models used to assess the climate sensitivity of future H2 emissions.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.