Controlling factors in stalagmite oxygen isotopic composition and the paleoprecipitation record for the last 1,100 years in Northeast Japan

Stable oxygen isotopic analysis was performed on the UT-A stalagmite with annual microbanding from the Uchimagi-do Cave in Iwate Prefecture on the Pacific side of Northeast Japan. High-resolution analysis of the uppermost portion of UT-A revealed a positive correlation between the stalagmite δ18O value and R ((summer precipitation–winter precipitation)/annual precipitation) over the last several decades. This correlation is the result of the distinct seasonal shift in precipitation δ18O. During the summer, rainfall with higher δ18O values arrives from the humid atmosphere over the Pacific Ocean. In the winter, comparatively little snowfall/rainfall, with lower δ18O values, arrives from the Japan Sea and is brought by Nangan cyclones (low-pressure systems that pass along the southern coast of Japan). In years with humid summers, large amounts of rainfall from the Pacific Ocean raise the δ18O values of the cave dripwater and stalagmites. Changes in precipitation over the last 1,100 years, reconstructed from the δ18O profile of the UT-A stalagmite, coincide with the historical records of famines and disasters triggered by rainfall excesses and shortages.