Carbonyl Sulfide, Methyl Chloride, and Methyl Bromide Measurements in the New Intermediate-depth South Pole Ice Core

过去，地球气候经历了戏剧性的变化，影响了全球范围内的物理、化学、地质和生物过程。这种变化在地球大气中留下了印记，二氧化碳和甲烷等痕量气体丰度的变化就是明证。反过来，大气微量气体成分的变化也影响了地球的气候。研究过去大气的成分变化有助于我们了解全球生物地球化学循环与地球-S气候相互作用的历史。有关过去大气成分的最可靠信息来自对极地冰芯中的空气的分析。该项目旨在生成相对短暂、非常低丰度的痕量气体的冰芯记录，以确定其大气水平过去的变化范围，并调查造成这种变化的全球生物地球化学循环的变化。该项目测量了三种这样的气体：羰基硫化物、甲基氯和甲基溴。羰基硫化物的变化可以指示初级生产力和二氧化碳的光合作用更新的变化。甲基氯和甲基溴的变化显著影响平流层臭氧的自然变化。此外，控制大气中甲基氯和甲基溴水平的过程与控制大气中甲烷水平的过程是相同的。测量将在南极的新冰芯进行，预计将提供4万年的记录。该项目的主要重点是建立整个全新世(过去11000年)的高质量痕量气体记录，以及从上一次冰期开始的更多探索性测量，包括2.9万-3.6万年前大气甲烷发生巨大变化的时期。由于南极冰层的温度较低，拟议的羰基硫化物测量预计将直接测量这种气体过去的大气可变性，而不需要对较温暖环境下的冰芯测量结果进行大的水解校正。此外，我们将测试这样一种预期，即在南极西部冰盖深处分割冰芯的最后一次冰期的同时测量将不需要水解损失校正。关于甲基氯，我们的目标是从南极洲的泰勒穹顶冰芯核实和改进现有的全新世大气历史。与泰勒穹顶的测量相比，我们的测量分辨率更高，这将使我们能够推导出甲基氯和甲烷之间更具统计学意义的关系。关于甲基溴，我们计划将现有的有2000年历史的数据库扩大到11000年。加在一起，甲基溴和甲基氯记录将对全新世期间平流层卤素的自然可变性提供强有力的基于测量的制约。此外，甲基溴记录将深入了解由于共同的来源和汇，在全新世期间甲基氯和甲烷之间的相互关系。

In the past, Earth's climate underwent dramatic changes that influenced physical, chemical, geological, and biological processes on a global scale. Such changes left an imprint in Earth's atmosphere, as shown by the variability in abundances of trace gases like carbon dioxide and methane. In return, changes in the atmospheric trace gas composition affected Earth's climate. Studying compositional variations of the past atmosphere helps us understand the history of interactions between global biogeochemical cycles and Earth?s climate. The most reliable information on past atmospheric composition comes from analysis of air entrapped in polar ice cores. This project aims to generate ice-core records of relatively short-lived, very-low-abundance trace gases to determine the range of past variability in their atmospheric levels and investigate the changes in global biogeochemical cycles that caused this variability. This project measures three such gases: carbonyl sulfide, methyl chloride, and methyl bromide. Changes in carbonyl sulfide can indicate changes in primary productivity and photosynthetic update of carbon dioxide. Changes in methyl chloride and methyl bromide significantly impact natural variability in stratospheric ozone. In addition, the processes that control atmospheric levels of methyl chloride and methyl bromide are shared with those controlling levels of atmospheric methane. The measurements will be made in the new ice core from the South Pole, which is expected to provide a 40,000-year record.The primary focus of this project is to develop high-quality trace gas records for the entire Holocene period (the past 11,000 years), with additional, more exploratory measurements from the last glacial period including the period from 29,000-36,000 years ago when there were large changes in atmospheric methane. Due to the cold temperatures of the South Pole ice, the proposed carbonyl sulfide measurements are expected to provide a direct measure of the past atmospheric variability of this gas without the large hydrolysis corrections that are necessary for interpretation of measurements from ice cores in warmer settings. Furthermore, we will test the expectation that contemporaneous measurements from the last glacial period in the deep West Antarctic Ice Sheet Divide ice core will not require hydrolysis loss corrections. With respect to methyl chloride, we aim to verify and improve the existing Holocene atmospheric history from the Taylor Dome ice core in Antarctica. The higher resolution of our measurements compared with those from Taylor Dome will allow us to derive a more statistically significant relationship between methyl chloride and methane. With respect to methyl bromide, we plan to extend the existing 2,000-year database to 11,000 years. Together, the methyl bromide and methyl chloride records will provide strong measurement-based constraints on the natural variability of stratospheric halogens during the Holocene period. In addition, the methyl bromide record will provide insight into the correlation between methyl chloride and methane during the Holocene period due to common sources and sinks.