Climate and vegetation study using environmental isotope types of stalactite at Seropan Cave, Gunung Kidul Yogyakarta

Climate and vegetation study using environmental isotopes (i.e., ¹³C, ¹⁴C and ¹⁸O) variations of stalactite has been conducted at Seropan cave, Gunung Kidul Karst area. The stalactite samples were collected from Seropan Cave at Semanu, Gunung Kidul, Yogyakarta. The objective of study is to understand the climate change, and vegetation types, temperature of atmosphere, age and stalactite growth rate through the interpretation of environmental isotopes (i.e., ¹³C, ¹⁴C and ¹⁸O) of stalactite samples. The environmental isotope content of stalactite samples were analysed through CaCO₃ compound that was found at the stalactite samples. The ¹³C content of samples is important to understand climate undulation and also vegetation variation. On the other hand, the variation of ¹⁸O and ¹⁴C contents is important to predict past temperature of atmosphere, and the age as well as stalactite growth rate, respectively. The result of environmental ¹³C isotope analysis showed that Gunung Kidul area in general can be classified as dry climate. It is also indicated that almost 87.5 % of local vegetation can be classified as dry vegetation C4 as can be seen from the variation of δ¹³C content that is -6 ‰ to +2 ‰ vs PDB. This can also mean that only 12.5 % of the time that the vegetation in the area is wet in which the variation of δ¹³C content is in the range -14 ‰ to -6 ‰ vs PDB. The variations of ¹⁸O contents of the samples (carbonate stalactite, or drip water) showed that the average temperature since 1621 to 2011 was around 19.5 °C. On the other hand, the variations of ¹⁴C contents of the samples showed that stalactite growth rate was around 0.1 mm/year or one mm in ten years. The result shows that the stalactite growth is very slow as generally expected in tropical area such as Gunung Kidul. (author)