[M-IS30_28PM1] 古気候・古海洋変動

[MIS30-13] アジア熱帯域の洞窟における現在の洞外気象と石筍成長の関係

*長谷川 航¹、渡邊 裕美子¹、松岡 廣繁¹、大沢 信二²、田上 高広¹ (1.京都大学大学院理学研究科地質学鉱物学教室、2.京都大学大学院理学研究科地球物理学教室)

キーワード：cave monitoring, speleothem, isotope, peleo-climate

IntroductionFor precise climate prediction, it is necessary to reconstruct high time and space resolution paleo-climate (especially past 2000 years) from paleo-climate proxies and assimilate the result to climate model. Tropical Asia, including Indonesia, is well affected by El Nino Southern Oscillation (ENSO). The ENSO does not only directly affect on precipitation in tropical Asia, but also indirectly on middle and high latitude climate through teleconnection [1]. In Indonesia, Watanabe et al. [2] suggested inverse-correlation between δ¹⁸O and δ¹³C in speleothems and instrumental precipitation. However, relationship between modern speleothem formation and surface weather is not revealed clearly.Therefore, the cave monitoring program, which included cave air temperature, relative humidity, airflow current, air CO₂ concentration monitoring and δ¹⁸O and δ¹³C analysis of dripwater and farmed speleothems, was initiated from 2011 in Petruk Cave (Central Java, Indonesia) in order to study the recording mechanism of precipitation variation into the δ¹⁸O and δ¹³C fluctuation in speleothems. Result and Discussion Air CO₂ concentration in Petruk Cave is fluctuated daily and seasonally until over 100 m deep site from the entrance.It is revealed that cave air CO₂ concentration may be a significant factor that controls stable isotope value in speleothems, because temperature, humidity and drip rate in Petruk cave are nearly stable. A scenario of precipitation recording is as follows: (1) surface rainfall cools outside air temperature; (2) cave airflow direction is inversed; (3) outside fresh air flows into the cave and air CO₂ concentration is dropped; (4) pCO₂ difference between cave air and dripwater becomes higher and calcite precipitation is promoted; (5) δ¹⁸O and δ¹³C in dripwaters and speleothems are decreased.In addition to above discussion, we will show you δ¹⁸O and δ¹³C values in dripwaters and farmed speleotems and confirm the scenario by these data.[1] Hastenrath (1991) Climate dynamics of the tropics. [2] Watanabe et al. (2010) Palaeogeography, Palaeoclimatology, Palaeoecology 293, 90?97.