Annual variation of oxygen isotopic contents of drifting snow and the isotopic contents of deposited snow layers at Mizuho Station, Antarctica

Oxygen isotopic contents of fresh snow drifts in the katabatic wind zone were measured. The samples were collected at a stage before forming deposited snow layers throughout the year. Besides, the oxygen isotope profiles of deposited snow layers at the same place were obtained. The δ^O contents of the snow drifts had high values in summer (-30～-40‰); in winter, values were generally low (above -50‰) but sometimes there were high values similar to those in summer. Deviation of relations between air temperature at sampling time and δ^O contents of the snow drifts under different weather conditions is discussed. Vertical profiles of δ^O contents of deposited snow are supposed to show a wide annual range and complicated annual variation, if such snow drifts accumulated continuously. However, those of deposited snow actually seen in the surface layers usually show a narrow range (-35～-45‰) and simplified pattern. Positions of maxima and minima in δ^O profiles of deposited snow have good correlations with layering of ice crusts which were formed during hiatus periods of snow deposition. These results indicate the importance of change of the isotopic contents after snow deposition for understanding the isotope profiles of deposited snow.