Collaborative Research: Inert Gas and Methane Based Climate Records throughout the South Pole Deep Ice Core

合作研究：整个南极深冰芯基于惰性气体和甲烷的气候记录

• 批准号: 1443710
• 负责人: Jeffrey Severinghaus
• 金额: $ 41.15万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1443710&HistoricalAwards=false
• 关键词: Collaborative; Research; Inert; Gas; Methane

Gases trapped in ice cores have revealed astonishing things about the greenhouse gas composition of the past atmosphere, including the fact that carbon dioxide concentrations never rose above 300 parts per million during the last 800,000 years. This places today's concentration of 400 parts per million in stark contrast. Furthermore, these gas records show that natural sources of greenhouse gas such as oceans and ecosystems act as amplifiers of climate change by increasing emissions of gases during warmer periods. Such amplification is expected to occur in the future, adding to the human-produced gas burden. The South Pole ice core will build upon these prior findings by expanding the suite of gases to include, for the first time, those potent trace gases that both trapped heat and depleted ozone during the past 40,000 years. The present project on inert gases and methane in the South Pole ice core will improve the dating of this crucial record, to unprecedented precision, so that the relative timing of events can be used to learn about the mechanism of trace gas production and destruction, and consequent climate change amplification. Ultimately, this information will inform predictions of future atmospheric chemical cleansing mechanisms and climate in the context of our rapidly changing atmosphere. This award also engages young people in the excitement of discovery and polar research, helping to entrain the next generations of scientists and educators. Education of graduate students, a young researcher (Buizert), and training of technicians, will add to the nation?s human resource base. This award funds the construction of the gas chronology for the South Pole 1500m ice core, using measured inert gases (d15N and d40Ar--Nitrogen and Argon isotope ratios, respectively) and methane in combination with a next-generation firn densification model that treats the stochastic nature of air trapping and the role of impurities on densification. The project addresses fundamental gaps in scientific understanding that limit the accuracy of gas chronologies, specifically a poor knowledge of the controls on ice-core d15N and the possible role of layering and impurities in firn densification. These gaps will be addressed by studying the gas enclosure process in modern firn at the deep core site. The work will comprise the first-ever firn air pumping experiment that has tightly co-located measurements of firn structural properties on the core taken from the same borehole.The project will test the hypothesis that the lock-in horizon as defined by firn air d15N, CO2, and methane is structurally controlled by impermeable layers, which are in turn created by high-impurity content horizons in which densification is enhanced. Thermal signals will be sought using the inert gas measurements, which improve the temperature record with benefits to the firn densification modeling. Neon, argon, and oxygen will be measured in firn air and a limited number of deep core samples to test whether glacial period layering was enhanced, which could explain low observed d15N in the last glacial period. Drawing on separate volcanic and methane synchronization to well-dated ice cores to create independent ice and gas tie points, independent empirical estimates of the gas age-ice age difference will be made to check the validity of the firn densification model-inert gas approach to calculating the gas age-ice age difference. These points will also be used to test whether the anomalously low d15N seen during the last glacial period in east Antarctic ice cores is due to deep air convection in the firn, or a missing impurity dependence in the firn densification models. The increased physical understanding gained from these studies, combined with new high-precision measurements, will lead to improved accuracy of the gas chronology of the South Pole ice core, which will enhance the overall science return from this gas-oriented core. This will lead to clarification of timing of atmospheric gas variations and temperature, and aid in efforts to understand the biogeochemical feedbacks among trace gases. These feedbacks bear on the future response of the Earth System to anthropogenic forcing. Ozone-depleting substances will be measured in the South Pole ice core record, and a precise gas chronology will add value. Lastly, by seeking a better understanding of the physics of gas entrapment, the project aims to have an impact on ice-core science in general.

冰芯中捕获的气体揭示了过去大气中温室气体成分的惊人信息，其中包括在过去 80 万年中二氧化碳浓度从未上升到百万分之 300 以上的事实。 这与今天百万分之 400 的浓度形成鲜明对比。 此外，这些气体记录表明，海洋和生态系统等温室气体的天然来源通过在温暖时期增加气体排放而充当了气候变化的放大器。 预计未来还会出现这种放大现象，从而增加人类产生的气体负担。 南极冰芯将在这些先前发现的基础上，扩大气体组，首次包括那些在过去 4 万年里既捕获热量又消耗臭氧的强效微量气体。 目前关于南极冰芯中惰性气体和甲烷的项目将以前所未有的精度改进这一重要记录的年代测定，以便可以利用事件的相对时间来了解痕量气体产生和破坏的机制，并随之而来的气候变化放大。 最终，这些信息将为在我们快速变化的大气背景下对未来大气化学净化机制和气候的预测提供信息。 该奖项还让年轻人对发现和极地研究感到兴奋，有助于培养下一代科学家和教育工作者。 研究生、年轻研究员（Buizert）的教育以及技术人员的培训将增加国家的人力资源基础。 该奖项资助南极 1500m 冰芯的气体年代学建设，使用测量的惰性气体（d15N 和 d40Ar——分别是氮和氩同位素比）和甲烷，并结合处理空气滞留的随机性质和杂质对致密化的作用。 该项目解决了科学认识上的根本差距，这些差距限制了气体年代学的准确性，特别是对冰芯 d15N 的控制以及分层和杂质在冰晶致密化中可能发挥的作用了解甚少。 这些差距将通过研究深部核心部位现代火的气体封闭过程来解决。 这项工作将包括有史以来第一个空气抽吸实验，该实验对取自同一钻孔的岩心的结构特性进行紧密的同位测量。该项目将测试由空气空气 d15N 定义的锁定层位的假设、二氧化碳和甲烷在结​​构上受不渗透层控制，而不渗透层又是由高杂质含量层产生的，其中致密化得到增强。 将使用惰性气体测量来寻找热信号，这可以改善温度记录，有利于冰晶致密化建模。 将在空气和有限数量的深部岩心样本中测量氖气、氩气和氧气，以测试冰期分层是否增强，这可以解释末次冰期观测到的低 d15N。 利用单独的火山和甲烷同步到年代清楚的冰芯来创建独立的冰和气体连接点，将对气体年龄-冰年龄差异进行独立的经验估计，以检查冰晶致密化模型-惰性气体方法的有效性计算气体年龄-冰河年龄差。 这些点还将用于测试南极东部冰芯末次冰期期间出现的异常低 d15N 是否是由于冷杉中的深层空气对流，或者冷杉致密化模型中缺少杂质依赖性所致。 从这些研究中获得的更多物理知识，加上新的高精度测量，将提高南极冰芯气体年代学的准确性，这将增强这个以气体为导向的核心的整体科学回报。 这将有助于澄清大气气体变化和温度的时间，并有助于了解痕量气体之间的生物地球化学反馈。 这些反馈关系到地球系统对人为强迫的未来反应。 臭氧消耗物质将在南极冰芯记录中进行测量，精确的气体年代学将增加价值。 最后，通过寻求对气体截留物理学的更好理解，该项目旨在对冰芯科学产生总体影响。