Wind-driven circulation on the northern Great Barrier Reef continental shelf in summer

Abstract

Observations of wind, atmospheric pressure, sea levels and current are presented for the northern (9°14′S) Great Barrier Reef continental shelf for November 1981 to May 1982. Strong low-frequency non-tidal oceanic fluctuations were observed, resulting in alternating northward and southward transport and a weak ‘mean’ circulation, and are the result of long ‘arrested’ topographic waves driven by a quasi-steady longshore wind stress and damped by turbulent bottom friction. The coefficient of friction for low-frequency currents is found to be proportional to the tidal velocities. The coefficient is also found to be much larger than that in the central (15–19°S) region of the Great Barrier Reef continental shelf, and this difference is attributed to the greatly enhanced energy dissipation by secondary circulation around coral reefs in the reef-studded northern region. Sough of Cape York (10·5°S), the primary effect of the cross-shelf wind is to complement the geostrophic set-up due to the longshore current. Intense tidal currents in the vicinity of Cape York combined with a dissipative western boundary in Torres Strait appear to prevent long wave propagation north of Cape York where a steady-state analytical model is used to show that both cross- and longshore wind components generate the reversing currents observed through Bligh Entrance.