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

Abstract

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.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.