Seasonal circulation and temperature variability near the North West Cape of Australia

Abstract

The circulation and temperature variability on the inner shelf near the North West Cape of Australia off Ningaloo Reef was investigated using field data obtained from two moorings deployed from 2004 to 2009. The results revealed that alongshore currents on the inner shelf were, on average, only weakly influenced by the offshore poleward (southward) Leeuwin Current flow, i.e., monthly averaged alongshore current velocities were ∼0.1 m s-1 or less. The presence of a consistent summer-time wind-driven equatorward (northward) counter flow on the inner-shelf (referred to in the literature as the Ningaloo Current) was not observed. Instead, the shelf waters were strongly influenced year-round by episodic subtidal current fluctuations (time scale 1-2weeks) that were driven by local wind-forcing. Analysis of the current profiles showed that periods of strong equatorward winds were able to overcome the dominant poleward pressure gradient in the region, leading to upwelling on the inner-shelf. Contrary to prior belief, these events were not limited to summer periods. The forcing provided by these periodic wind events and the associated alongshore flows can explain much of the observed temperature variability (with timescales < 1 month) that influences Ningaloo Reef.