Dynamics of the turbidity maximum in King Sound, tropical Western Australia

Abstract

King Sound is a 100-km-long embayment located in tropical northwestern Australia with a spring tidal range of 11 m. This is the second largest tide in the world after the Bay of Fundy in Canada. Intertidal areas cover about 800 km2. The upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m−3. Field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998. The tide was a propagating wave, shoaling and dissipating by friction as it entered the sound. This mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb. An evaporation-driven salinity maximum zone was found in the upper reaches of the sound, and this was also where the turbidity maximum occurred. Tidal pumping by the tidal asymmetry and, possibly, the biological filter formed by muddy marine snow, trapped the fine sediment in the upper regions of King Sound. Wind-driven waves contributed significantly to entrainment of bottom fine sediment, possibly through wave pumping of the sediment and not wave-induced orbital velocities. Field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height.