Ocean currents measured concurrently on and off the Sydney area continental shelf

Abstract

Recording current meters, a GEK, and XBT'S were used to study on and off-shelf currents for a 10 day period. Oscillatory currents with frequencies 3-8 cph were observed quite frequently at a mid-shelf mooring (depth 140 m). They were perhaps due to internal waves and were often associated with sudden increases or decreases in current speed. On two occasions the speed increases occurred when meteorological fronts passed over. The horizontal oscillatory velocity components of two of the best wave examples showed clear evidence for clockwise polarization. At the edge of the shelf (180 m), current meters 10 and 50 m above the bottom, while not showing internal waves, showed a current somewhat variable in speed (mean: 20 cm/sec; maximum 50 cm/sec), but reasonably constant in direction (northward) for the experiment duration. At this time the main southward flowing core of the East Australian Current was 120 km out from the edge of the shelf, while the region out to 50 km from the shelf contained variable surface currents. The current in the deeper water at the edge of the shelf was tentatively labelled a counter current.