Climatic controls on the stable isotopic composition of precipitation in Northeast Asia

An examination of oxygen and hydrogen isotopic compositions of precipitation in NE Asia from the IAEA/WMO data set reveals that many sites have a distinct winter-summer seasonal pattern in deuterium excess (d-) values that appears to reflect different climatic conditions. To further understand this pattern, stable isotopic data were obtained for individual rainfall events over a 2 yr period at Jeju Island, Korea. The δ18O- and δD-values of precipitation at Jeju Island are not dependent upon temperature. However, the deuterium excess values, which range from 3.0 to 40.6‰, show a distinct seasonal variation with higher d-values in winter (>~15‰) and lower values in summer (~10‰). Such a seasonal variation is closely related to different air masses affecting the island during different seasons: a cold-dry continental polar air mass in winter and a hot-humid maritime tropical air mass in summer.