Estimation of the concentrations of greenhouse gases in ancient air using ice core analysis

点击翻译按钮获取中文摘要

Precise analysis technique with dry and wet air extractions for the CO_2, CH_4 and N_2O concentrations and delta^<13>C of CO_2 from polar ice core was newly developed independently to reconstruct their ancient levels. The overall precision of the present measurements, including air extraction, was estimated to be better than *1.0 ppmv for CO_2, *10 ppbv for CH_4, *2ppbv for N_2O and 0.05* for delta^<13>C. By using these experimentaltechnique, three ice cores, two from the Antarctica one from Greenland, were analyzed. The results obtained in this study are summarized as follows:1. The CO_2,CH_4 and N_2O concentrations were fairly stable during almost entire period of the Holocene with small fluctuations of the concentration. However, after 250 years BP, the concentrations of these gases increased with time due to human activities.2. The CO_2,CH_4 and N_2O concentrations from an ice core near the Yamato Mountains, Antarctica were obviously lower than the pre-industrial Holocene values, s … More uggesting that this core was formed in the glacial period. During the glacial period, the CO_2 concentrations varied almost out of phase with d13C, which may imply that CO_2 exchange occurred between the atmosphere and the oceans through phytoplankton activities.3. The pre-industrial/pre-agricultural levels of the CH_4 concentration from the Arctic core were higher than 54*10 ppbv than those from the Antarctic core, which is suggested that natural CH_4sources had been stronger in the northern hemisphere than in the southern hemisphere, reflecting the greater extent of boreal compared with austral lands. The present concentration difference of atmospheric CH_4 between northern and southern high latitudes was estimated to be almost three time as much as we have measured for the pre-industrial/pre-agricultural era. From this fact, it was suggested that a large amount of CH_4 was being released into the atmosphere from anthropogenic CH_4 sources especially in the northern hemisphere and/or OH radicals have decreased more rapidly in the northern hemisphere, perhaps due to an increase of the atmospheric CO concentration by fossil fuel combustion. Less