Cross-shelf seawater exchange controls the distribution of temperature, salinity, and neritic carbonate sediments in the Great Australian Bight

Abstract

The seasonally averaged wind stress of the Great Australian Bight (GAB) during the austral winter is directed to the east along the shelf and results in downwelling that extends to depths of 250 m. This downwelling is enhanced in the eastern GAB through the outflow of cold saline water formed in the broad shallow regions of the GAB and gulfs. During the austral summer, the averaged wind stress field of the GAB is anticyclonic with upwelling favorable winds along much of the coastline. In general however, significant slope upwelling is only observed in the eastern and western GAB where the shelf is narrow. Upwelling there provides nutrients to support the planktic and pelagic communities and the observed distribution of benthic invertebrate communities that lead to the formation of neritic carbonate sediments. At the shelf break of the central GAB where the shelf is very wide, the observed cross-shelf distributions of temperature, salinity, and sediments indicate that downwelling occurs year round. The implied lack of nutrients is argued to explain the smaller communities of invertebrates found at the shelf edge (100–250 m) in these areas. A previous numerical study is cited to show that summer downwelling very likely results from a convergence of the deep ocean and poleward Sverdrup transports. The unique aspect of this integrated oceanographic-sedimentological investigation is to tie outcomes of that numerical study with extant observations and benthic habitat to provide a consistent picture of how cross-shelf exchange regulates water properties and benthos in the GAB.