Great Australian Bight

The Great Australian Bight is a massive oceanic bight, or open bay. It sits off the central and western parts of the southern Australian coastline.

This feature is located mostly south of the expansive Nullarbor Plain. The Nullarbor Plain is a very flat, dry area that straddles South Australia and Western Australia. There are two main ways to define the extent of this bight. The International Hydrographic Organization (IHO) includes it in the Indian Ocean. However, the Australian Hydrographic Service (AHS) classifies it as part of the Southern Ocean.

The Bight formed about 50 million years ago. This happened when the supercontinent Gondwana broke apart. This massive geological event separated Antarctica from Australia.

European explorers first encountered the area in 1627. A Dutch navigator named François Thijssen sailed along the western margins. Later, the English navigator Matthew Flinders accurately charted the coast in 1802. He did this during his circumnavigation of the Australian continent. An English explorer named Edward John Eyre later performed a land-based survey.

The coastline features many different geological structures. Near Cape Pasley, the coast sits on ancient crystalline rocks from the Yilgarn craton. The coast curves northeast with a parallel escarpment. This area includes the Israelite Plain and a chain of coastal lagoons. As the coast turns east, the escarpment creates the Baxter Cliffs. Further east, the Bunda Cliffs, or Nullarbor Cliffs, extend for 100 kilometers to the Head of the Bight.

The western Eyre Peninsula has a different look. Its coastline is made of aeolianite limestone. This limestone forms rocky capes, bays, and islands like Fowlers Bay and Smoky Bay. Waves and currents have shaped these into beaches and dunes.

Ocean currents and seasonal patterns drive the local biology. The Bight's waters are often oligotrophic, meaning they are low in nutrients. This is because the nearby Nullarbor Plain has no surface drainage. However, a process called upwelling changes this in certain areas. During summer and autumn, deep ocean water rises toward the surface near the Eyre Peninsula. This upwelling brings essential nutrients to the surface waters. These nutrients support high levels of primary productivity.

This nutrient influx supports a complex food web. The upwelling creates cool patches of surface water. These patches support high densities of zooplankton. These tiny organisms are the foundation of the ecosystem. High densities of small fish, such as sardines and anchovy, live here. Juvenile southern bluefin tuna also migrate into the Bight to feed on these resources. The Bight is also incredibly diverse in its seaweed. The macroalgal assemblage includes more than 1,200 different species.

The region is a critical habitat for several marine mammals. Southern right whales migrate to the Bight during the southern hemisphere winter. They specifically use the Head of Bight to calve and breed. These whales do not feed until they return to the Antarctic. The Australian sea lion is also a resident species. These sea lions breed in small colonies along the Bight's cliffs. The sea lion is currently listed as near threatened. The southern right whale is also listed as endangered under Australian law.

Human activity has shaped the history of the Bight. It has long been used for fishing, whaling, and shellfish industries. Southern bluefin tuna is a very popular fishing target. Since the 1960s, companies have also explored the area for oil and gas. This has caused significant community opposition and debate. Many people worry about the environmental impact of resource extraction. In 2016, the Australian Senate even began an inquiry into oil and gas production there. Companies like BP, Chevron, and Equinor have all engaged with these exploration proposals. Towns like Ceduna and Eucla provide access to this remote coastline.