Development of gas microanalysis method in ice cores

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Information of the atmospheric composition over the past 200,000 years in ice cores is stored in air bubbles and clathrate hydrates, of which sizes are as small as 1mm or less. In order to interpret information of the atmospheric composition precisely, high reliability is required in the analysis method. In this study, considering gas fractionations caused by the transition process of the air bubble to the clathrate air-hydrates, we aimed at development of the method to measure the local composition of N_2 and O_2.We have applied a micro-Raman scattering method to the measurements, and we have established the method to correct the data for crystal anisotropy of the clathrate hydrates. As a result, we have successfully clarified the gas fractionation process in ice sheets. We proved that the micro-Raman scattering method is a highly reliable method to reveal the distribution of N_2/O_2 ratio in the individual clathrate hydrates. For the absolute precision of the gas compositions, however, the data should be compared with those obtained by the chemical analysis. We also developed a system of the quantitative analysis of gases using the gas chromatography I mass spectrometer.