Nutrient inputs into the central Great Barrier Reef (Australia) from subsurface intrusions of Coral Sea waters: a two-dimensional displacement model

In the central Great Barrier Reef (17°-20°S), near-bottom intrusions of cool, nutrient-rich water upwell episodically onto the outer shelf several times each summer (October-April). Near-bottom water temperature at the shelf break was found to be a useful but conservative predictor of the volume of intruded water and inorganic nutrient (N, P) inputs in cross-shelf sections. Large upwelling events that occur at least once per summer may displace up to 1/3 of the water on the outer shelf and import phosphate and nitrate stocks 2-6 times those normally present in outer-shelf waters. The concurrently displaced outer-shelf waters export substantial amounts of organic N and P. Net N and P imports are on the order of 75% and 30% of gross N and P imports, respectively. Interannual variations in nutrient inputs from the Coral Sea are related to the number and intensity of intrusive upwelling events occurring each summer. Comparison with other nutrient fluxes suggests upwelling is a substantial source of "new" N and P to the central Great Barrier Reef.