ENVIRONMENTAL PARAMETERS CONTROLLING STALAGMITE GROWTH IN TROPICAL AREAS: NEW INSIGHTS FROM CAVE MONITORING AT PETRUK CAVE, CENTRAL JAVA, INDONESIA

摘要

To elucidate environmental parameters controlling stalagmite growth in tropical areas, we conducted cave monitoring throughout a year in Petruk Cave, central Java, Indonesia. We compared stalagmite growth rate with the cave's environmental parameters, air temperature, drip rate, calcium concentration of the drip waters, and pCO(2)-air. We found a relationship where stalagmite growth rate is fast (slow) when pCO(2)-air is low (high) during dry (rainy) season, suggesting that pCO(2)-air controls stalagmite growth. Note that this is a first study that reports that dramatic pCO(2)-air reduction occurring during dry season in a tropical cave controls stalagmite growth. Additionally, we discuss the mechanism of pCO(2)-air fluctuation. Monitoring results show that pCO(2)-air fluctuation is divided into two phenomena: seasonal fluctuations and daily fluctuations. Dramatic pCO(2)-air reduction during the dry season is likely to result from a decline of plant activity due to little rainfall. On the daily scale, pCO(2)-air reached to the minimum around 6 a.m. and maximum around 2-4 p.m., although it is not obvious whether this is due to plant activity or cave ventilation. Also, dynamic pCO(2) pCO(2)-air reduction was observed following cave ventilation driven by the sudden drop of outside air temperature due to a downburst during severe rain. This suggests that heavy rainfall in short duration is also one factor that controls cave ventilation and pCO(2)-air.