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

本项目的目的是了解为什么大气中的一氧化二氮（N2 O）含量在最后一个冰河时期（约20，000 - 100，000年前）比随后的温暖时期（10，000年前至今）低，以及为什么它在冰河时期的气候变化中波动。 一氧化二氮是一种导致现代全球变暖的温室气体。人们认为，现代变暖反过来会导致土壤和海洋中细菌产生的一氧化二氮的自然来源增加，从而产生“正反馈”。“然而，这些来源将增加的数量是不确定的，因为一氧化二氮产生的不同方式，以及它们对温暖气候的敏感程度，并不为人所知。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，但尚未应用于所讨论的时间段。 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。 反过来，这将有助于预测未来的变化，并有助于理解为什么地球的气候从冰河时期转变到温暖时期，然后再回来。 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，并有助于了解自然排放与气候变化的联系。该项目将开发两个记录的分子内的位置偏好的氮-15在N2 O。一个记录跨越了最后一次冰川消退（10，000 - 21，000年前），当时大气中N2 O浓度上升了30%，另一个记录跨越了最后一个冰河时期的千年气候变化，当时N2 O变化较小（Heinrich Stadial 4和Dansgaard Oeschger 8，35，000 - 41，000年前）。这些记录将用于了解氮循环中的哪些变化导致大气N2 O浓度变化，以及N2 O排放与气候变化之间的联系机制。理想情况下，研究这两个不同的时间段将隔离千年的气候响应纠缠在一起的完整的冰消序列，创建一个更清晰的图片如何N2 O地球化学响应气候变化。这项工作还将允许探索同位素示踪剂，用于原位生产N2 O，特别是在尘埃冰中污染大气信号。该项目将使用来自南极泰勒冰川的一套独特的、年代久远的冰样品，以及在俄勒冈州州立大学实验室运行的定制气体提取线上的连续流同位素比质谱。该奖项反映了NSF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。

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.