Structure of coastal upwelling events observed off the south-east coast of South Australia during February 1983–April 1984

Abstract

Observations of upwelling along the south-east coast of South Australia during the summers of 1983 and 1984 are presented. In situ measurements were obtained from a number of current meters moored across the continental shelf near 37.5ºS.,139.5ºE. These were complemented by wind and sea level measurements along the coast and also monthly hydrographic surveys. Differences between summer and winter regimes are discussed in both physical and dynamical terms. The summer weather pattern gives rise to winds which are favourable to upwelling along this coast more than 50% of the time (i.e. winds from the south-east quarter). The evolution of two upwelling events and the associated shelf circulation are documented. Salient features include the offshore transport of water in a shallow surface layer 0 (20 m) in response to south-easterly winds; an onshore compensatory flow occurs almost immediately below. The summer thermocline shoals soon after the onset of winds favouring upwelling, leading to pronounced cross-shelf surface-temperature gradients with cooler (upwelled) water at the surface near the coast. The surfaced thermocline moves offshore and attains an equilibrium position in the vicinity of the shelf edge (after 4-5 days), as shown by infrared satellite images, while water from depths of 250-300 m encroaches onto the shelf. Alongshore currents reach speeds of more than 50 cm s^-1 in the outer-shelf region and are strongly influenced by the position of the upwelling front. Brief comparisons are drawn with other upwelling regions.