The tidal and longer-period circulation of Capricornia, Southern Great Barrier Reef

Abstract

Between June and December 1983, nine current meters and three water level recorders were deployed on the continental shelf and slope of the Capricornia Section of the Great Barrier Reef between Fraser Island (25ºs.) and the mouth of the Capricorn Channel (23ºs.) on the east coast of Australia. Tidal analyses of the hourly data set reveal an amplification of the semi-diurnal tides as they propagate north- westward into the Capricorn Channel. The results of a numerical model of tidal flow show excellent agreement with observations. The daily averaged (non-tidal) currents are highly variable and produce complex circulation patterns, but with a mean flow generally alongshore to the north-west. Comparisons with previous drifter studies and satellite-tracked buoy data suggest that the south-eastward flowing East Australian Current drives a large clockwise eddy, in the lee of the Swain Reefs, located east of the study region. It is postulated that this eddy, in addition to the generally north-westward wind stress, contributes to the north-westward flow within the study region. Temperatures recorded by the deployed instruments and temperature profiles from conductivity-temperature-depth casts confirm that tidal and longer period variablity contribute to upwelling onto the continental shelf.