Transfer of inland salts to the marine environment at the head of Spencer Gulf, South Australia

Abstract

Upper Spencer Gulf is linked by a narrow tidal channel to an extensive system of salt marshes, channels and salt pans overlying Cainozoic sediments of the Pirie-Torrens Basin in arid South Australia. The gulf here is characterised by a vigorous tidal regime with a spring range of 3–4 m, current velocities reaching 1.0 m s −1, and salinities greater than that estimated from evaporation alone. We suggest that the anomalously high salinities are maintained by input from interstitial brines from the northern salt pan corridor, and by the “scavenging” effect of surface water after occasional heavy rains. These processes are particularly important in buffering the salinity of tidal waters in winter, when evaporation is reduced. Our hypothesis is based on the distribution of total salts, major ions, selected trace elements and the 87Sr/ 86Sr isotopic ratio in samples of surface and interstitial water collected during 1986–1988, and on oceanographic measurements of the tidal regime. A removal rate of the order of 10 kg s −1 of total salts from inland brines to tidal water has been derived from hydrodynamical simulations of the system.