ABSTRACT

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.