[M-IS14] Paleoclimatology and paleoceanography

[MIS14-P01] High-resolution records for the last 200 years decoded from stable isotopes of cascade tufas on Kobaru Beach, Tokunoshima Island in Kagoshima Prefecture, Japan

★Invited Papers

Akira Murata¹, Hirokazu Kato², *Akihiro Kano¹ (1.Graduate School of Science, The University of Tokyo, 2.Teikyo University of Science)

Keywords:tufa, stable isotope, PDO

Tufa is a potential archive for high-resolution paleoclimate study due to its rapid growth rate and the development of annual laminations. However, tufas in a fluvial setting generally lack continuity of the deposition because the growth of tufa blocks a stable flow condition sustained for a long time over several decades. This is the reason why tufas are rarely utilized as paleoclimate archives. Here, we study the samples from cascade-type tufas at Kobaru Beach on Tokunoshima Island, Kagoshima Prefecture, which have grown continuously for more than 200 years. Based on the isotopic analysis and textural observation, we selected a cascade tufa as the most suitable material for paleoclimate analysis. This tufa sample is dated from 1828 to 2020 AD by lamina-counting. The carbon isotope ratio of this tufa indicates a declining trend in the recent 70 years, which likely reflects the consumption of fossil fuel (Suess effect). Based on the analysis of meteoric water samples at Naze located 100 km NE of Kobaru Beach, we found that the seasonality of precipitation is strongly correlated with the oxygen isotope ratio of meteoric water and tufa. The seasonality reconstructed by the oxygen isotope ratio of tufa broadly corresponds to the observed seasonality at Naze, in terms of the general trend and the cyclic change with a ~20-year frequency. The cyclic change also occurs in the Pacific Decadal Oscillation (PDO), suggesting that the Pacific sea surface temperature influences the precipitation around Tokunoshima Island.