17:15 〜 18:30
[MIS16-P01] 広島県および岐阜県産石筍の安定酸素同位体比への温度効果
キーワード：石筍、古気候、安定酸素同位体、炭酸凝集同位体、陸域気温
Stalagmites from caves are excellent archives of terrestrial paleoclimate information. Stalagmite δ18O values are basically controlled by two major factors, temperature of calcite formation and cave drip water δ18O derived from the local precipitation. The latter factor involves the changes in climatic factors including the monsoon intensity, moisture trajectory, and seasonality of precipitation. It is, however, not easy to determine relative importance of two fundamental controls, by conventional isotopic compositions alone. Carbonate clumped isotope thermometry is a resolution to this problem, which can directly reconstruct paleo-temperature regardless of drip water δ18O.
Recently, stalagmite studies focusing on temperature signals were reported for the late Pleistocene to middle Holocene stalagmites from Japan (e.g., Mori et al., 2018). We recently measured carbonate clumped isotope (Δ47) from 50 layers of Hiro-1 stalagmite (18−4 ka) from Hiroshima Prefecture and successfully separated signals of temperature changes and drip water δ18O in the Hiro-1 δ18O values (Kato et al., 2021) using equations of temperature-dependencies of δ18O and Δ47 (Tremaine et al., 2011; Kato et al., 2019). An important finding in Kato et al. (2021) was that meteoric water δ18O (drip water δ18O) per se changes depending on temperature.
In this study, the authors newly analyzed Δ47 values from more than 60 layers of OT-02 stalagmite (63−35, 8−3 ka) collected from Ohtaki cave, Gifu prefecture, of which U-Th ages and δ18O values had been already analyzed by Mori et al. (2018). The Δ47 measurements were performed using a dual inlet mass spectrometer (Finnigan MAT-253) at Kyushu University.
In the relevant interval of mid-Holocene (8 to 4 ka), OT-02 stalagmite shows a similar Δ47 profile with Hiro-1, the peak of warming around the Hypsithermal (6−5 ka) after a slight cooling around 7 ka. This agreement suggests that Δ47 values of the two Japanese stalagmites are reliable proxies of terrestrial temperature. In the period of 63−35 ka, Δ47 values of OT-02 exhibit periodic fluctuation relating Dansgaard-Oeschger cycles with 3−5 ºC cooling in Heinrich events 4−6. As considered by Mori et al. (2018), temperature variation is likely a major controlling factor of OT-02 δ18O. Reconstructed paleo drip water δ18O by subtracting temperature effect from OT-02 δ18O shows a correlation with the reconstructed temperature, which was also recognized in Hiro-1 stalagmite in Hiroshima. However, the correlation in OT-02 is even stronger than that of Hiro-1. It can be assumed that the drip water δ18O in Gifu reflect the precipitation ratio of summer rainfall with higher δ18O and winter snow/rainfall with lower δ18O, which differs depending on climatic periods.
References
Kato, H. et al (2019) Seasonal temperature changes obtained from carbonate clumped isotopes of annually laminated tufas from Japan: discrepancy between natural and synthetic calcites. GCA 244, 548−564.
Kato, H. et al (2021) Influences of temperature and the meteoric water δ18O value on a stalagmite record in the last deglacial to middle Holocene period from southwestern Japan. QSR 253.
Mori, T. et al (2018) Temperature and seawater isotopic controls on two stalagmite records since 83 ka from maritime Japan. QSR 192, 47−58.
Recently, stalagmite studies focusing on temperature signals were reported for the late Pleistocene to middle Holocene stalagmites from Japan (e.g., Mori et al., 2018). We recently measured carbonate clumped isotope (Δ47) from 50 layers of Hiro-1 stalagmite (18−4 ka) from Hiroshima Prefecture and successfully separated signals of temperature changes and drip water δ18O in the Hiro-1 δ18O values (Kato et al., 2021) using equations of temperature-dependencies of δ18O and Δ47 (Tremaine et al., 2011; Kato et al., 2019). An important finding in Kato et al. (2021) was that meteoric water δ18O (drip water δ18O) per se changes depending on temperature.
In this study, the authors newly analyzed Δ47 values from more than 60 layers of OT-02 stalagmite (63−35, 8−3 ka) collected from Ohtaki cave, Gifu prefecture, of which U-Th ages and δ18O values had been already analyzed by Mori et al. (2018). The Δ47 measurements were performed using a dual inlet mass spectrometer (Finnigan MAT-253) at Kyushu University.
In the relevant interval of mid-Holocene (8 to 4 ka), OT-02 stalagmite shows a similar Δ47 profile with Hiro-1, the peak of warming around the Hypsithermal (6−5 ka) after a slight cooling around 7 ka. This agreement suggests that Δ47 values of the two Japanese stalagmites are reliable proxies of terrestrial temperature. In the period of 63−35 ka, Δ47 values of OT-02 exhibit periodic fluctuation relating Dansgaard-Oeschger cycles with 3−5 ºC cooling in Heinrich events 4−6. As considered by Mori et al. (2018), temperature variation is likely a major controlling factor of OT-02 δ18O. Reconstructed paleo drip water δ18O by subtracting temperature effect from OT-02 δ18O shows a correlation with the reconstructed temperature, which was also recognized in Hiro-1 stalagmite in Hiroshima. However, the correlation in OT-02 is even stronger than that of Hiro-1. It can be assumed that the drip water δ18O in Gifu reflect the precipitation ratio of summer rainfall with higher δ18O and winter snow/rainfall with lower δ18O, which differs depending on climatic periods.
References
Kato, H. et al (2019) Seasonal temperature changes obtained from carbonate clumped isotopes of annually laminated tufas from Japan: discrepancy between natural and synthetic calcites. GCA 244, 548−564.
Kato, H. et al (2021) Influences of temperature and the meteoric water δ18O value on a stalagmite record in the last deglacial to middle Holocene period from southwestern Japan. QSR 253.
Mori, T. et al (2018) Temperature and seawater isotopic controls on two stalagmite records since 83 ka from maritime Japan. QSR 192, 47−58.