| Summary: | Nitrous oxide is an important greenhouse gas that has both natural and anthropogenic sources in the modern atmosphere (Ciais et al., 2013). This project expanded the knowledge of the history of atmospheric N2O in the geologic past by measuring N2O concentrations in air trapped in very old polar ice. A method for taking precise measurements of N2O from small ice core samples was perfected by optimizing both gas chromatographic methods and corrections for solubility effects a melt-refreeze extraction procedure. The method setup was tested by analyzing ice core samples from the Taylor Glacier, Antarctica blue ice region previously measured for N2O by a mass spectrometric method and comparing the results. The method was then implemented to produce measurements of N2O levels in recently discovered ice that ranges 1-2.7 million years old, from the Allan Hills in Antarctica. Measurements of nitrous oxide concentrations from the Allan Hills ice cores dating from the Mid-Pleistocene and Pre-Mid-Pleistocene Transition (MPT and Pre-MPT) time periods give insight into how atmospheric N2O levels behaved millions of years ago when glacial-interglacial climate cycles were less severe than in more recent times. The maximum concentrations in this study are similar to the maxima during younger interglacial periods, but concentrations do not reach the low levels characteristic of full ice ages in the post-800ka time period. The range of concentrations is about 217-312 ppb, as compared to the range of 199-303 ppb during younger time periods.
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