Characteristics of Oxygen Stable Isotopic Ratio in Precipitations in Niigata Prefecture, Japan

LI Chong, KANO Naoki, UENO Yuichi, HANABUSA Mitsuru, JIAO Yurong, IMAIZUMI Hiroshi, WATANABE Naoki

doi:10.3769/radioisotopes.59.93

Time-course of oxygen stable isotopic ratios(i.e., δ¹⁸O)as well as annual or seasonal variation of δ¹⁸O has been examined to investigate the sources, the passing route and characteristics of precipitations in Niigata Prefecture. The precipitation samples have been mainly collected with a filtrating bulk sampler at the rooftop of Niigata University from 1999 to 2008. Furthermore, backward trajectories analyses have been also conducted for these samples taken sequentially for a short period.<BR>Consequently, the following features have been mainly clarified for the precipitations in Niigata Prefecture. (1)The δ¹⁸O values varied between −25.14‰ and −1.60‰, while the mean value of δ¹⁸O in each year was from −8.37‰(in 2006)to −7.33‰(in 2001). (2)As for the comparison among sampling points, the mean value of δ¹⁸O at seaside spots(i.e., Niigata City and Joetsu City)or marine spots(i.e., Sado City)is larger than that of inland spots(Shitada Village and Nagaoka City). (3)δ¹⁸O value was generally small in the rainy season, and relatively large in summer, and small in winter. (4)Decreasing δ¹⁸O content with time, as predicted by Rayleigh models of atmospheric vapor condensation, is a predominant feature of sequentially sampled rainfalls, particularly for precipitations taken during passage of typhoons.

Characteristics of Oxygen Stable Isotopic Ratio in Precipitations in Niigata Prefecture, Japan

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