| Summary: | 碩士 === 國立成功大學 === 地球科學系專班 === 98 === This study has conducted systematic research on a cavern system in Shanshan, Kaohsiung City. Water samples including rain, cave water, and groundwater, bedrock, soil, and speleothem samples were collected for stable isotope and elemental concentration analyses. A 14.3-cm long stalagmite, 08SS02-B, is the main material for this thesis. The stalagmite reveals clear growth lamination bands, and contains pure calcite shown by XRD analysis. Two stalagmites were dated by ICP-MS 230Th/U dating method at National Taiwan University. Stalagmite 08SS02-B was grew between 28,680±410 and 29750±250 year ago in the Last Glacial Maximum, yielding a growth rate of 0.134mm/yr; whereas Stalagmite 08SS02-C with 10.5-cm in length was grew between 14000 and 14370±600 year ago belonging to the deglaciation，giving a growth rate of 0.294mm/yr. The slower growth rate of Stalagmite 08SS02-B indicates that climate during the Last Glacial Maximum was cold and dry. Missing speleothem deposits in the cave during the Holocene might be due to active tectonics and humid/hot climates in the area.
Based on the Mg/Ca and Sr/Ca ratios in the water and stalagmite, we can calculated the distribution coefficients of Mg and Sr between calcite and its parent solution, being KMg = 0.0336 and KSr = 0.0682, respectively. These values are close to the stalagmite collected from Dagangshan area (DGS01) 0.0255 and 0.1216, although 08SS02-B contains 10 times lower Mg and Sr than these of DGS01. This means that the distribution coefficients are mainly controlled by the ratios in the parent solution, water temperature and crystal growth rate. The Mg/Sr in stalagmite may be used as a paleo-temperature proxy.
Using thermal equilibrium equation of oxygen isotope fractionation between calcite and its parent solution, we obtain -10.22? (PDB) for the calcite under 24.7oC and the ?18OH2O of -8.55? (SMOW). This values is much lighter than the measured ?18O of surface samples in Stalagmite 08SS02-B, the later is -6.2 ~ -6.4?（PDB）. This result shows again that the stalagmite was not grown in the Holocene period, rather, it grew in a cold/dry period. Furthermore, we have estimated that the ?18O value of surface water during the Last Glacial Maximum was at least 2? heavier than that of modern water. This finding is important in terms of paleoclimate study, and it agrees previous studied in the eastern China.
According to the ?18O and ?13C records of 08SS02-B, we interpret that Even though in the Last glacial Maximum in South Taiwan the climatic conditions were cold and dry during 28,680 ~ 29,000 year ago; and relatively warm and wet during 29,000 ~ 29,800 year ago. This is the first high-resolution paleoclimate record in Taiwan.
|
|---|
