Geochemical significance of 14C, 3H, δ18O, δ2H and 87Sr/86Sr isotope data for the Dongrae and Haeundae hot spring waters, Busan, South Korea

Abstract

Dongrae and Haeundae are representative hot spring areas that have been used as spas for more than 1,000 years in the southern Korean Peninsula. These hot springs have water temperatures >58 °C and are located along the southeast coastal area of the peninsula. We used 14C, 3H, δ18O, δ2H, and 87Sr/86Sr isotope data for the Dongrae and Haeundae hot spring waters collected over 2004–2014 to investigate the groundwater cycle and heat source for these hot springs. The stable isotope compositions of O and H suggested meteoric origin of the hot spring waters. The 87Sr/86Sr ratios for the Dongrae and Haeundae hot spring waters have been steady for 11 years at 0.70567 ± 0.00002 and 0.70607 ± 0.00002, respectively, suggesting that they are in a near equilibrium state. The 14C age of the Dongrae hot spring waters ranges from 1,401 to 2979 years BP, and that of the Haeundae hot spring waters from 1930 to 6687 years BP. We observed a strong correlation between 87Sr/86Sr and 14C, as well as δ18O. Therefore, the hot springs in the Busan area were supposed to be heated by a paleo-heat source, suggesting that there may be no current heat source under the present crustal conditions. This study also demonstrates that monitoring of the 87Sr/86Sr ratio and 14C in the groundwater and deep thermal water can be used as a proxy for tracing the heat source of geothermal waters such as hot springs and an indicator of groundwater mixings between upper and lower aquifers in granite area.