Deciphering Changes in Atmospheric Nitrous Oxide Concentration During the Last Ice Age Using the Intramolecular Site-Preference of Nitrogen Isotopes

该项目的目的是了解为什么在上一个冰期(大约20,000-100,000年前)大气中一氧化二氮(N2O)的含量低于随后的暖期(10,000年前到现在)，以及为什么在冰期内的气候变化期间，大气中的一氧化二氮含量波动。一氧化二氮是一种温室气体，导致现代全球变暖。据认为，现代气候变暖将反过来导致土壤和海洋中细菌产生的一氧化二氮自然来源增加，从而产生“正反馈”。然而，这些来源将增加的数量还不确定，因为一氧化二氮的不同产生方式，以及它们对气候变暖的敏感度，还不是很清楚。该项目将测量南极洲冰川中非常大的古代空气样本中一氧化二氮分子的独特性质。这种方法可以区分产生一氧化二氮的不同微生物过程，但它还没有被应用到相关的时间段。这些数据将提供有关自然气候变化如何影响一氧化二氮生产的信息。这反过来将有助于预测未来的变化，并有助于理解为什么地球气候从冰期转变为暖期，然后又回来。温室气体同位素组成的冰芯记录有助于确定过去自然源和汇强度的变化，并有助于理解自然排放与气候变化之间的联系。这个项目将开发两个关于N-15在N2O中的分子内位置偏好的记录。一项记录跨越了最后一次冰川消融(10,000-21,000年前)，当时大气中N2O的浓度上升了30%，另一项记录跨越了上一次冰河时期N2O变化较小的千年尺度的气候变化(Heinrich Staial 4和Dansgaard Oeschger 8，35,000-41,000年前)。这些记录将被用来了解氮循环中哪些变化导致大气N2O浓度变化，以及哪些机制将N2O排放与气候变化联系起来。理想情况下，研究这两个不同的时间段将分离出与整个去冰川序列纠缠在一起的千禧年气候反应，从而更清楚地了解N2O生物地球化学是如何应对气候变化的。这项工作还将允许探索一种同位素示踪剂，用于原位产生N2O，这种N2O污染了特别是尘土飞扬的冰中的大气信号。该项目将使用一套独特的、日期准确的南极洲泰勒冰川冰样和俄勒冈州立大学实验室运行的定制天然气提取线上的连续流动同位素比质谱仪。该奖项反映了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。

The objective of this project is to understand why the nitrous oxide (N2O) content of the atmosphere was lower during the last ice age (about 20,000-100,000 years ago) than in the subsequent warm period (10,000 years ago to present) and why it fluctuated during climate changes within the ice age. Nitrous oxide is a greenhouse gas that contributes to modern global warming. It is thought that modern warming will in turn cause increases in natural sources of nitrous oxide from bacteria in soils and the ocean, creating a "positive feedback." However, the amount these sources will increase is uncertain because the different ways that nitrous oxide are produced, and how sensitive they are to warmer climate, are not well known. This project will measure a unique property of the nitrous oxide molecule in very large ancient air samples from a glacier in Antarctica. This method can distinguish between different microbial processes that produce nitrous oxide but it has not been applied yet to the time periods in question. The data will provide information about how natural climate changes affect nitrous oxide production. This, in turn, will be useful for predicting future changes and for understanding why the Earth's climate shifts from ice ages to warm periods and back again. Ice-core records of greenhouse gas isotopic composition are useful for determining past changes in natural source and sink strengths and for understanding how natural emissions are linked to climate change. This project will develop two records of the intramolecular site preference of Nitrogen-15 in N2O. One record spans the last deglaciation (10,000-21,000 years ago) when atmospheric N2O concentration rose by 30 percent, and the other record spans millennial-scale climate changes during the last ice age when N2O varied by smaller amounts (Heinrich Stadial 4 and Dansgaard Oeschger 8, 35,000-41,000 years ago). The records will be used to understand what changes in the nitrogen cycle caused atmospheric N2O concentration to vary and what mechanisms link the N2O emissions to climate change. Ideally, studying the two different time periods will isolate the millennial climate responses entangled with the full deglacial sequence, creating a clearer picture of how N2O biogeochemistry responds to climate change. This work will also allow exploration of an isotopic tracer for in situ production of N2O that contaminates the atmospheric signal in particularly dusty ice. The project will use a unique, well-dated suite of ice samples from Taylor Glacier, Antarctica and continuous flow isotope ratio mass spectrometry on a custom gas extraction line operated in the Oregon State University laboratory.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.