Estimating submarine discharge of fresh groundwater from a volcanic island using a freshwater budget of the coastal water column

Abstract

The magnitude of submarine fresh groundwater discharge (SFGD) was estimated using a freshwater budget of the coastal water, which was calculated from salinity anomalies off a volcanic island, Jeju, Korea. We obtained high‐resolution profiles of salinity from the entire coastal area of Jeju Island using accurate CTD sensors. Lower salinity anomalies relative to the pristine offshore seawaters were observed and assumed to be a result of SFGD on the basis of negligible surface runoffs from the island and the relatively high levels of 222Rn in the low‐salinity waters. The SFGD flux during the study period calculated from a freshwater budget of the water column was 2.5−3.8 × 106 m3 d−1, which is close to the long‐term average based on the inland water balance. Our study shows that SFGD can be accurately and easily measured using a freshwater budget of the coastal waters off a highly permeable coastal zone with little surface runoff.