81Br, 37Cl, and 87Sr Studies to Assess Groundwater Flow and Solute Sources in the Southwestern Great Artesian Basin, Australia

The Great Artesian Basin (GAB) is a water source for more than 200,000 residents in central Australia. This study investigates the relationship of bromine and chlorine stable isotopes to groundwater chemistry in a confined aquifer in the southwestern GAB to better understand its flow regime and solute sources. δ81Br values range from +0.66‰ near the recharge area to +1.04‰, 150 km down gradient, while δ37Cl ranges from 0‰ to -2.5‰. While δ37Cl decreases with distance from the recharge area, δ81Br increases slightly. Bromide in the recharge area is possibly enriched from selective atmospheric processes causing fractionation in marine aerosols during transport. When confined and isolated from the atmosphere, increases in bromide and to a lesser extent strontium concentrations may contribute through water-rock interaction to changes in isotopic signatures along the flow system. 87Sr/86Sr values range from ∼0.717 near the recharge zone to a depleted 0.708 160 km down gradient.