Investigating links between atmospheric chemistry and climate using oxygen isotope measurements of sulfate and nitrate from Greenland ice cores

从冰芯记录中观察到温室气体浓度与温度指标之间的密切关系，对我们理解温室气体与气候之间的关系产生了深远的影响。然而，尽管经过了几十年的研究，我们对温室气体浓度变化的原因仍然没有确切的认识。在决定大气中对气候变化(如CH4)和人类健康(如CO)至关重要的痕量气体的寿命方面，羟基自由基(OH)起着重要作用，并在很大程度上决定了大气的氧化能力。从冰芯中提取的硝酸盐和硫酸盐气溶胶的氧同位素组成(&amp；#8710；17O)提供了有关过去大气化学的信息，可作为评估古大气化学模型模拟的工具。南极沃斯托克冰芯对硫酸盐和硝酸盐的初步测量表明，与工业化前的全新世相比，上一次冰川时期极地地区的对流层臭氧浓度较高，中高纬度地区的羟基浓度较高。目前正在使用包含同位素示踪剂的全球化学-气候模型对这些数据集进行定量解释，并证明了硝酸盐和硫酸盐对氧化剂浓度的敏感性。目前，在北半球的冰期-间冰期时间尺度上没有硫酸盐和硝酸盐的测量结果。我们在这里的目标是将现有的关于冰川-间冰期时间尺度的观测数据集扩展到北半球，以检验这一时间尺度上甲烷浓度的变异性在很大程度上(50%)是由于对流层羟基浓度的变化，正如陆地植被模拟所表明的那样。我们还将提供一个初步的研究，看看OH的变化是否可以部分解释在两个突然的气候事件中甲烷的可变性。有关甲烷汇强度的定量信息将改变我们将甲烷记录定量解释为陆地气候条件的代理的能力，从而提高我们对气候变化与甲烷源和汇之间的机械反馈的理解。了解气候变化对大气化学和大气氧化能力的影响，对于预测未来气候变化对当地和区域空气污染和人类健康的影响至关重要。该项目将涉及在跨学科和国际背景下培训两名研究生(一名美国人和一名法国人)使用地球化学分析工具。

Observation of the tight correlation between greenhouse gas concentrations and indicators of temperature from the ice core record has had a profound impact on our understanding of the relationship between greenhouse gases and climate. However, despite many decades of research, we still do not have a firm understanding of the causes of the variability in greenhouse gas concentrations. The hydroxyl radical (OH) plays a major role in determining the lifetimes of atmospheric trace gases important to both climate change (e.g. CH4) and human health (e.g. CO), and largely determines the oxidative capacity of the atmosphere. The oxygen isotopic composition (∆17O) of nitrate and sulfate aerosols extracted from ice cores provides information about the chemistry of past atmospheres, and can serve as a tool for evaluating model simulations of paleo atmospheric chemistry. Initial measurements of sulfate and nitrate ∆17O from the Vostok, Antarctica ice core suggest higher tropospheric O3 concentrations in polar-regions and higher OH concentrations in the mid- to high-latitudes during the last glacial period relative to the preindustrial Holocene. Quantitative interpretation of these data sets is ongoing using a global chemistry-climate model containing the isotopic tracers, and demonstrates the sensitivity of nitrate and sulfate ∆17O to oxidant concentrations. Currently, no measurements of sulfate and nitrate ∆17O exist on the glacial-interglacial timescale in the Northern Hemisphere. Our goal here is to expand the existing observational data set on the glacial-interglacial timescale to the Northern Hemisphere in order to test the hypothesis that variability in methane concentrations on the on this timescale is largely (50%) due to changes in tropospheric OH concentrations, as has been suggested by terrestrial vegetation modeling. We also will provide a first look into whether changes in OH may partially explain variability of methane during two abrupt climate events. Quantitative information about the sink strength of methane will transform our ability to quantitatively interpret the methane record as a proxy for terrestrial climate conditions, and as such improve our understanding of the mechanistic feedbacks between climate change and the sources and sinks of methane. Understanding the affects of a changing climate on atmospheric chemistry and the oxidizing capacity of the atmosphere is crucial for predicting the impacts of future climate change on local and regional air pollution and human health. The project will involve training two graduate students (one US and one French) in the tools of geochemical analysis in an interdisciplinary and international context.