Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS19] Paleoclimatology and paleoceanography

Thu. May 30, 2019 9:00 AM - 10:30 AM 304 (3F)

convener:Yusuke Okazaki(Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University), Akira Oka(Atmosphere and Ocean Research Institute, The University of Tokyo), Michinobu Kuwae(Center for Marine Environmental Studies), Hitoshi Hasegawa(Faculty of Science and Technology, Kochi University), Chairperson:Hitoshi Hasegawa

9:15 AM - 9:30 AM

[MIS19-18] Terrestrial paleoclimate since 80 ka recorded in stable and clumped isotopes of two stalagmites obtained from the Pacific side of the Japanese islands

*Shota Amekawa1, Hirokazu Kato1, Akihiro Kano1, Kenji Kashiwagi2, Taiki Mori3, Ryoko Senda3, Chuan–Chou Shen4 (1.Graduate School of Science, The University of Tokyo, 2.Graduate School of Science and Engineering for Research, University of Toyama, 3.Graduate School of Integrated Sciences for Global Society, Kyushu University, 4.Department of Geosciences, National Taiwan University)

Keywords:clumped isotope, speleothem paleoclimatelogy

Terrestrial paleoclimate during late Quaternary has been broadly reconstructed by oxygen isotope (δ18O) of stalagmites. Previous studies have pointed out that stalagmite δ18O is largely associated with change in δ18O of meteoric water due to amount effect and shift of vapor sources, but also can be influenced by temperature change. One of solutions for evaluating the temperature effect is carbonate clumped isotope thermometer. Clumped isotopes are isotopologues in which rare isotopes are doubly or multiply substituted. In case of CO2 generated from reaction of carbonate and phosphoric acis, the measuring target is 13C18O16O (mass of 47). Previous studies have shown that measured abundance of clumped isotopes is slightly more than the stochastic abundance and its excess or “clumping” (Δ47) comes from thermodynamic stability, which allows us to reconstruct temperature during carbonate precipitation only by Δ47 of the generated CO2. In this study, Δ47 and stable isotopes are applied to two stalagmites from the Pacific side of the Japanese islands, which should not be affected by vapor from Indian Ocean and Japan Sea.
Two analyzed stalagmites (KA01 and 03) were obtained from Taiki town, Mie prefecture, Japan. 32 U-Th age points determined at National Taiwan University reveal that KA01 was dated from ca. 14 ka to ca. 1 ka and KA03 (Mori et al., 2018) was from ca. 80 ka to ca. 20 ka as well as the Holocene. δ18O changes of KA01 and KA03 show similar trends with the cave records in south Chinese (e.g. Hulu cave), but the amplitude of the δ18O changes was reduced in half.
Results of our Δ47 values require reconsideration of the previous interpretation for the Chinese stalagmite δ18O, dominant control by δ18O of meteoric water. A reconstructed temperature at the top of KA01 is consistent with modern temperature at the cave. The whole trend of reconstructed temperature combined with δ18O of modern rainfall indicates that δ18O changes of KA01 are mainly controlled by temperature changes instead of rainfall δ18O. Δ47 of KA03 yields higher temperature during cool periods of Heinrich events (HE), which apparently contradicts with previous studies. Before and after HEs, the carbon isotopic value increases by 0.5–1 ‰, indicating degassing of 13C-depleted CO2 from dripwater and carbonate precipitation in the conduit of the host rock because of reduced water supply. Drying during HEs could have made the surface of the stalagmite dry and resulted in apparent contradictory temperature. This study verifies that δ18O change should be used together with Δ47 for robust interpretation of the stalagmite records.