The density-driven circulation of the coastal hypersaline system of the Great Barrier Reef, Australia

•Deep inshore GBR waters conduct thermohaline circulation of hypersalinity.•Longshore transport affects the degree of hypersalinity in the deep inshore waters.•The flushing time of coastal hypersaline GBR waters is 2–3 weeks.•The thermohaline circulation in the deep inshore waters reduces as inshore SST rise.•First 3D modelling of hypersaline thermohaline circulation in deep inshore GBR

The coastal hypersaline system of the Great Barrier Reef (GBR) in the dry season, was investigated for the first time using a 3D baroclinic model. In the shallow coastal embayments, salinity increases to c.a. 1‰ above typical offshore salinity (~ 35.4‰). This salinity increase is due to high evaporation rates and negligible freshwater input. The hypersalinity drifts longshore north-westward due to south-easterly trade winds and may eventually pass capes or headlands, e.g. Cape Cleveland, where the water is considerably deeper (c.a. 15 m). Here, a pronounced thermohaline circulation is predicted to occur which flushes the hypersalinity offshore at velocities of up to 0.08 m/s. Flushing time of the coastal embayments is around 2–3 weeks. During the dry season early summer, the thermohaline circulation reduces and therefore, flushing times are predicted to be slight longer due to the reduced onshore-offshore density gradient compared to that in the dry season winter period.