Submarine groundwater discharge revealed by 224Ra and 223Ra in Coffs Harbour, Australia

Submarine groundwater discharge (SGD) is an important link between the land and ocean. In this study, eddy diffusivity coefficients (Kh) and SGD rates were examined off the Jetty Beach in Coffs Harbour (Australia) in September 2017 and 2018. In order to estimate Kh, the apparent age and SGD, two short-lived radium isotopes 224Ra and 223Ra were measured along a shore-perpendicular transect and beach groundwater. Estimated SGD rates were 3.3 and 5.4 cm day−1 in 2017 and 12.7 and 9.3 cm day−1 in 2018, based on average 224Ra and 223Ra groundwater endmember activities. The SGD flow was higher in 2018 due to the combination of a spring tide and rainfall events that took place prior to sampling.