Rainfall and hydrological controls on speleothem geochemistry during climatic events (droughts and typhoons): An example from Seopdong Cave, Republic of Korea

A five year-old, 20cm-long soda straw (SD-1) was analyzed geochemically to delineate the relationship between the geochemical record and climatic behavior. The growing tip of the soda straw was marked on July 18, 1999, and the sample was collected on July 16, 2004, thus the growth period of this speleothem is well constrained. During the five years the soda straw grew about 20cm, a mean growth rate of about 4cm/year. Fast growth rate of this speleothem enabled not only to understand seasonal variations of geochemical data but also to compare these data directly with outside climatic variations near the cave. ²¹⁰Pb_ex (excess or unsupported ²¹⁰Pb) results suggest that the overall pattern of ²¹⁰Pb_ex changes as well as the frequency and relative intensity of their peaks show a strikingly similar pattern to that of the amounts of precipitation in the study area. This suggests that ²¹⁰Pb_ex was transported into the cave with infiltrating rainwater mostly during rainy summers because ²¹⁰Pb_ex is a particle-reactive element. Controlling detailed growth rates by the ²¹⁰Pb_ex fluctuations, it can be noticed that δ¹⁸O compositions vary very little in spite of significant droughts and typhoon events, whereas δ¹³C values clearly display impacts of a severe drought from 2000 to 2001. The Sr/Ca, Ba/Ca, U/Ca and Mn/Ca ratios coincide with the δ¹³C trends and show anomalies during the drought period. These coeval trends strongly indicate that hydraulic factors in vadose zone that were directly controlled by the amount of rainfall, influenced on the geochemical imprints of the SD-1. This study illustrates the behavior of an atmospheric radionuclide (²¹⁰Pb_ex), the O and C stable isotopes and trace elements in calcite speleothems and, furthermore, implies that they can be used to detect short-term climatic behavior, including climatic extreme events, as well as the long-term climatic fluctuations in the past.