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.

Is the East Australian Current causing a marine ecological hot-spot and an important fisheries near Fraser Island, Australia?

“…Middleton et al (2007) investigated interannual variability of GAB events and Nieblas et al (2009) proposed a simple model to predict GAB Chl-a variability. Middleton et al (2014) contrasted upwelling and enhanced marine productivity along the narrow eastern and western shelfs of the GAB. All-year round downwelling was proposed as an upwellingsuppressing mechanism that reduces marine productivity in the central GAB.…”

Observations of vertical turbulent nitrate flux during summer in the Great Australian Bight

“…Subsequent observations have revealed the presence of subsurface chl a maxima (~ 50 m depth) associated with summertime stratification (McClatchie et al, 2006) may be a key source of elevated primary productivity measured in the eGAB during the summertime upwelling season (van Ruth et al, 2010). Over 500 km to the west in the central GAB (cGAB), the collision of the coastward Sverdrup transport with the seaward topographic transport is expected to drive year-round downwelling to depths greater than 200 m at the shelf-break (Middleton and Bye, 2007;Middleton et al, 2014). Hence, while the FC is likely to be important for deep upwelling along the slope to depths of 300 to 600 m (Middleton and Bye, 2007), downwelling at the shelf in the cGAB is expected to suppress nutrient supply and limit primary production.…”

Spatial and temporal variations in female size at maturity of a Southern Rock Lobster (Jasus edwardsii) population: A likely response to climate change

“…As the continental shelf broadens across the central Great Australian Bight (regions 1 and 2), downwelling at the shelf break [42] is expected year round [38][43], and summer warming of shallower shelf waters results in the establishment of a deep warm isothermal layer, known as the Great Australian Bight warm pool, with near uniform temperatures >17°C observed to depths greater than 40 m [40] (Fig 1). Similarly, Region 4 is characterised by a broad and shallow shelf area.…”