日本地球惑星科学連合2015年大会

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セッション記号 M (領域外・複数領域) » M-IS ジョイント

[M-IS34] 古気候・古海洋変動

2015年5月27日(水) 18:15 〜 19:30 コンベンションホール (2F)

コンビーナ:*山田 和芳(静岡県 文化・観光部 文化学術局 ふじのくに地球環境史ミュージアム整備課)、池原 実(高知大学海洋コア総合研究センター)、入野 智久(北海道大学 大学院地球環境科学研究院)、岡 顕(東京大学大気海洋研究所)、岡崎 裕典(九州大学大学院理学研究院地球惑星科学部門)、北場 育子(立命館大学古気候学研究センター)、北村 晃寿(静岡大学理学部地球科学教室)、佐野 雅規(総合地球環境学研究所)、中川 毅(立命館大学)、林田 明(同志社大学理工学部環境システム学科)

18:15 〜 19:30

[MIS34-P18] 大分県稲積洞における大気モニタリングと滴下水の化学分析結果

*進藤 辰郎1渡邊 裕美子1三島 壮智1大沢 信二1田上 高広1 (1.京都大学大学院理学研究科地球惑星科学専攻)

キーワード:古気候学, 石筍, 滴下水, 鍾乳洞内大気モニタリング

10 month cave air monitoring and chemical analysis of drip water were conducted at Inazumi underwater cave, Oita, Japan, from February to December, 2014, to understand the processes and mechanism of recording paleoclimate in stalagmite. Cave air CO2 was measured for the cave monitoring, and EC, pH, HCO3- and Ca2+ were measured for chemical analysis of drip water.

Special sampling techniques were designed for two sampling sites, SS2 and SS3, to highlight the relationship between cave air CO2 and drip water chemistry. At SS2, the drip waters, before and after hitting on three handrails arranged in tandem in limestone cave (SS2-U, -M2, -M3 and -L, respectively), were sampled. At SS3, the drip waters, befor contacting with the cave air (BCWA) and after hitting on the artificial stalagmite, were sampled (BCWA, SS3-U, -M, -L, respectively).

At SS2, as the drip water hit on the handrails, HCO3-, Ca2+ and EC showed decreasing trend respectively and this trend became significant during winter when the cave air CO2 was low. Only pH was negatively correlated with other drip water parameters the above. This suggests that the two conditions, 1) the cave air CO2 is lower and 2) water film gets thinner as the drip water hits on the handrails, promote more CO2 degassing and CaCO3 precipitation.

At SS3, HCO3- and Ca2+ between BCWA and the drip water after contacted with the cave air showed almost the same concentration during summer, high cave air CO2 season, however, marked significant margin between them during winter, low cave air CO2 season. This result suggests that once drip water contacts with lower cave air CO2, more CO2 degassing and CaCO3 precipitation are promoted.

S.I.cc, standing for Saturation Index of Calcium Carbonate, and ∆pCO2, the difference of partial pressure of drip water (pCO2-drip water) and of cave air (pCO2-cave air), were calculated if CO2 degassing and CaCO3 precipitation takes place or not. S.I.cc showed positive value at SS2 and SS3 during almost all monitoring periods, indicating CaCO3 is produced almost all the time. However, ∆pCO2 showed frequently negative value at SS2 and SS3, indicating that CO2 is not degassed from the drip water and the following CaCO3 precipitation is not taken place and most of drip water sampled already degassed CO2.

This research implied that CO2 variation is a main forcing factor to control HCO3- and Ca2+, main components in drip water to form CaCO3-made-laminae used for reconstructing paleoclimate; however, the calculation of ∆pCO2 showed that CaCO3 would not be produced from drip water. To solve the contradiction, another approach such as development of new sampling method will be necessary.