Trapped Gases in the Greenland Ice Sheet: CO2 Isotope Ratios & Concentration in the Past Atmosphere

作为格陵兰冰盖项目的一部分，该项目将把大气二氧化碳浓度和同位素组成记录追溯到全新世。这将通过测量来自格陵兰冰芯的相对较小的（250克）冰样本中大气气体中二氧化碳的浓度和C13/C12比率来完成。该技术将把样品放在一个专门设计的真空系统中，并将冰升华到零下80摄氏度的冷阱表面。通过这个过程，气体将被释放。这样得到的CO2样品的量将被精确地测量，其C13/C12比值将被确定。样品中的空气将通过分子筛回收。每单位冰所含的空气量将记录下封盖时冰盖的高度。二氧化碳与空气的比例将被精确测量（大于0.5%），这将记录被捕获大气样品的二氧化碳浓度优于1ppm。冰川时期大气二氧化碳的C13/C12比率也将被测量。在冰期/冰期后过渡期间，这一比率的变化将是对当时发生的大（80 ppm） CO2浓度变化机制的重要检验。其他与气候相关的问题包括对末次冰期结束和冰期/后冰期过渡、新仙女木事件和Dansgaard-Oeschger事件的详细研究。这些浓度和稳定同位素数据与二氧化碳的放射性碳年代相结合，将能够测试与过去和未来气候变化有关的碳循环模型。

As part of the Greenland Ice Sheet Project, this project will extend the atmospheric CO2 concentration and isotope composition record back through Holocene times. This would be done by measuring the concentration and C13/C12 ratio of carbon dioxide in atmospheric gases trapped in relatively small (250 g) samples of ice from Greenland ice cores. The technique would be to place the sample in a specially designed vacuum system and to sublime the ice onto the surface of a -80 c cold trap. The gas will be released by this procedure. The amount of CO2 sample so obtained would be accurately measured and its C13/C12 ratio determined. The air in the sample would be recovered on molecular sieve. The amount of air, per unit of ice, would record the altitude of the ice sheet at the time of seal-off. The ratio of CO2 to air would be accurately measured (to better than 0.5%) which would record the CO2 concentration of the sample of trapped atmosphere to better than 1ppm. The C13/C12 ratio of atmospheric carbon dioxide during glacial times will also be measured. The change of this ratio during the glacial/post-glacial transition will be an important test of the proposed mechanisms for the large (80 ppm) CO2 concentration change that occurred at that time. Other climate-related questions include a detailed study of the end of the last glacial and the glacial/post-glacial transition, the Younger Dryas event, and the Dansgaard-Oeschger events. These concentration and stable isotope data, combined with radiocarbon dates for CO2, will enable testing of carbon cycle models relating to past and future climate change.