Global cycles of greenhouse gases during the last 100 years implied by firn air data

分别从南极YM85和格陵兰岛NGRIP的降雪层不同深度采集了空气样品，分析了CO2和CH4的浓度及其同位素比值。YM85深度70m处的CO_2和CH_4浓度分别为304ppm和970ppb。用一维数值模型估算了它们的有效年龄约为90岁。用过去大气CH4浓度加权的年龄分布函数的线性组合可以重建降雪层中CH4浓度的垂直分布，从而迭代地得到最可信的过去大气CH4记录，从而很好地再现了降雪层中CH4的观测剖面。同样的方法也被应用于碳和氢同位素比率的重建。根据大气浓度历史及其碳、氢同位素比值计算了大气CH4收支的时间变化。这一结果表明，生物质燃烧产生的甲烷排放量在近100年内将是重要的。

Air samples were collected from different depths of the firn layer at YM85, Antarctica, and NGRIP, Greenland, respectively, and analyzed for CO_2, and CH_4, concentrations and their isotopic ratios. The CO_2, and CH_4 concentrations at 70m depth at YM85 are 304ppm and 970ppb, respectively. Their effective age was estimated to be about 90 years by using a one-dimensional numerical model. The vertical distribution of CH_4 concentration in the firn layer can be reconstructed by a linear combination of the age distribution functions weighted by the atmospheric CH_4 concentrations in the past.Therefore, the most plausible past atmospheric record of CH_4 can be derived iteratively so that its observed profile in the firn layer was reproduced well. Same method was also applied to the reconstructions of carbon and hydrogen isotopic ratios. Temporal variations of atmospheric CH_4 budget was calculated from the atmospheric histories of concentration and its carbon and hydrogen isotopic ratios. This result shows that the CH_4 emission from biomass burning would be important during last 100 years.