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

[U05-P02] Annual record of boron isotopes of massive Porites coral skeleton from Chichijima Island in the western North Pacific

*Kaoru Kubota¹, Ryo Nakano², Masafumi MURAYAMA², Tsuyoshi Ishikawa¹, Yusuke Yokoyama³, Atsushi Suzuki⁴ (1.Kochi Institute for Core Sample Research, JAMSTEC, 2.Faculty of Agriculture and Marine Science, Graduate School of Integrated Arts and Sciences, Kochi University, 3.Atmosphere and Ocean Research Institute, The University of Tokyo, 4.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology)

Keywords:boron isotope, multi-collector ICPMS, ocean acidification

Long-term pH record in the surface ocean is limited to the very recent period, for the last three decade, hampering our understanding of natural variability of surface seawater pH and recent anthropogenic decline due to surface ocean carbon dioxide concentration increase (ocean acidification). Boron isotope composition of skeleton of long-living massive Porites coral, a known seawater pH proxy, can potentially provide continuous, long-term record. Here we present result of boron isotope measurement for the century-long living massive Porites coral from Chichijima Island in the western North Pacific in annual time resolution. Boron isotope ratio was measured by using multi-collector ICPMS, Thermo Scientific Neptune installed at Kochi Core Center, in a precision of ±0.1 permil (2 standard deviation). A method of boron isotope measurement for the coral sample was modified from the previous application, namely anion exchange column was skipped to make the measurement simple and enhance the sample throughput. The new annually resolved boron isotope record shows good agreement with previously reported one from Guam Island, at least in decadal timescales.