[U-05] Advanced understanding of Quaternary and Anthropocene hydroclimate changes in East Asia

[U05-P05] High-resolution Holocene records of a stalagmite from maritime Japan

*Shota Amekawa¹, Akihiro Kano¹, Kenji Kashiwagi², Taiki Mori³, Fumito Shiraishi⁴, Chuan-Chou Shen^5,6,7 (1.Graduate School of Science, The University of Tokyo, 2.Department of Environmental Biology and Chemistry, Faculty of Science, University of Toyama, 3.Graduate School of Integrated Sciences for Global Society, Kyushu University, 4.Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, 5.High-precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, 6.Global Change Research Center, National Taiwan University, 7.Research Center for Future Earth, National Taiwan University)

Keywords:Stalagmite, Stable isotope, Trace element, East Asian summer monsoon, Holocene

In East Asia, the climatic factor for the lowered meteoric water δ¹⁸O during mid-Holocene than the last glacial period is still controversial. Previous interpretations on stalagmite δ¹⁸O were recently re-examined with new records from the maritime Japan, in eastern part of the Asian monsoon region beyond the influence from Indian summer monsoon (Mori et al. 2018). However, their stalagmite presented limited records in the Holocene section because of low growth rate. Here, we report another stalagmite from the same cave (Kiriana cave in Mie Prefecture), which provides high-resolution records of stable isotopes and trace element during Holocene.
The ages of the 34-cm-long stalagmite were determined at 17 horizons through Uranium-Thorium dating method at the National Taiwan University. Stable isotopes were measured at 0.2-mm intervals using an isotope ratio mass spectrometer (Thermo Finnigan DeltaPlus) connected with an on-line gas separation and introduction system (GASBENCH II) at the Kyushu University. Trace element analysis was performed with inductivity coupled plasma optical emission spectrometer (iCAP7200, Thermo Fisher Scientific) at the Hiroshima University.
The stalagmite δ¹⁸O displays similar temporal patterns with the Chinese records but exhibits much smaller amplitude of δ¹⁸O than the Chinese records. This result supports the idea of Mori et al. (2018) that the stalagmite δ¹⁸O record from this cave is a superimposed signal of variations in air temperature and seawater δ¹⁸O, rather than the hydroclimatic control on meteoric water δ¹⁸O . On the other hand, δ¹³C of the stalagmite has more than 2‰ shift from mid- to late-Holocene with ~1‰ excursions in millennial timescale. The variation synchronized with Mg/Ca suggests that the δ¹³C change is largely affected by prior calcite precipitation (PCP) from the infiltrating water in the karst bedrock, which generally increases under a dry condition. Supposing that δ¹³C record of this stalagmite reflects PCP induced by precipitation change, we propose that precipitation or EASM variability is recorded more clearly in δ¹³C rather than δ¹⁸O of stalagmite in maritime Japan.