[M-IS15] Paleoclimatology and Paleoceanography

[MIS15-25] Short-term and long-term cyclic variations recorded in oxygen isotope ratios of Cascade Tufa on Kobaru Beach, Tokunoshima island, Japan

*Akira Murata¹, Hirokazu Kato¹, Akihiro Kano¹ (1.The University of Tokyo)

Keywords:cascade tufa, oxygen isotope ratio, Pacific Decadal Oscillation

Tufas, which develop in limestone areas of temperate to subtropical zones, are potential media for recording terrestrial climate. Previous studies have revealed that riverine tufas could provide high-resolution records of weeks or months, but they have problems in continuity that can only cover 20-30 years intervals (Matsuoka et al., 2001; Kawai et al., 2006; Hori et al., 2008). Andrew (2006) pointed out this problem and suggested that cascade-type tufas, which develop like mounds or stalagmites under waterfalls, should be targeted.
In this study, we focused on cascade tufas developed on Kobaru beach, Tokunoshima Island, Kagoshima prefecture, and obtained records for the past 200 years. Oxygen isotope ratios are characterized by a periodicity of about 20 years. Such periodic trends are also observed in the amount of precipitation at Naze, Amami-Oshima Island, and also in the Pacific Decadal Oscillation (PDO). The cascade tufa sample with monthly resolution also shows oxygen isotope variations in response to short-term rainfall events.
These results suggest that rainfall events respond to variations in sea surface temperature (SST) around Tokunoshima Island and affect oxygen isotope ratios of rainwater. As a result, oxygen isotope ratios of tufas have recorded such changes.