CIRCULATION AND WATER MASS CHARACTERISTICS OF THE SOUTHERN GREAT-BARRIER-REEF

Data acquired during a winter may) cruise of the RV Franklin to the so uthern Great Barrier Reef indicate that the dynamics of the shelf/slop e region are governed by the tides, the poleward-flowing East Australi an Current (EAC), and the complex topography. Over the Marion Plateau in water deeper than approximately 100 m, the EAC appears to drive a s low clockwise circulation. Tides appear to be primarily responsible fo r shelf/slope currents in the upper layers, with evidence of nutrient uplift from the upper slope to the outer shelf proper in the Capricorn Channel. Elsewhere, the bottom Ekman flux of the strongly poleward-fl owing EAC enhances the sloping isotherms associated with the longshore geostrophic balance, pumping nutrient-rich waters from depth to the u pper continental slope. Generally, shelf waters are cooler than oceani c waters as a consequence of surface heat loss by radiation. A combina tion of heat loss and evaporation from waters flowing in the shallows of the Great Sandy Strait appears to result in denser 'winter mangrove waters' exporting low-oxygen, high-nutrient waters onto the shelf bot h north and south of Fraser Island; these subsequently mix with shelf waters and finally flow offshore at approximately 100 m depth, just ab ove the salinity-maximum layer, causing anomalous nutrient values in t he region of Fraser Island.