Australia: The Land Where Time Began

A biography of the Australian continent 

This sinkhole is situated on the coastal plain of the Cape Range Peninsula, about 1.7 km from the west coast. There is only 1 entrance that inclines down, at an angle of 30^o to the horizontal, for about 70 m. As the water table is about 5 m below the surface in this area, the sinkhole is flooded. An anchialine ecosystem is an inland, underground system that is connected to ocean tides. It is the only known anchialine system in Australia, and in the Southern Hemisphere.

Drowned sinkholes with anchialine systems usually have seawater forming the bottom layer, with upper layers of fresh to brackish water. They are usually stratified by a number of factors such as light, temperature and salinity. The marine layer usually has low oxygen levels, and above the interface there are layers that decrease in salinity towards to the water surface, the uppermost layer usually being brackish or fresh. In the Canary Islands and the Caribbean, they support a wide variety of relict life forms related to ancient faunas in the marine layer. An example are remipeds, a recently discovered crustacean that is found only in these environments. There are also sulphur bacteria in this layer.

The surface water in the Bundera Sinkhole is about half the salinity of seawater, with a gradient of increasing salinity towards the marine layer. At the entrance, there is a deep scum of algae on the surface. This scum is the basis of the food chains in the system, the browsers on the algae being mostly many types of crustaceans, some of which are related to Tethyan species. The very stable zonation and layering in this sinkhole is believed to be the result of a combination of factors, the small surface opening, the arid conditions of the area around the entrance, and the fact that light penetrates to the interface between the marine water and the layers above it. There is a strong density interface, and sharp thermocline (zone of temperature change) at 8 m, the temperature increasing about 5^o C. Light doesn't penetrate below the interface with the marine water, resulting in the ecosystem above the interface being run by photosynthesis, but below the interface it is chemosynthesis that drives the food chains. Between about 8 m and 16 m, the salinity increases from about half that of seawater to the same as seawater. In the thermocline zone, there are veil-like colonies of sulphur bacteria suspended in the thermocline that release hydrogen sulphide gas as a by-product.

Remipeds that live below the interface are endemic to the Bundera Sinkhole, with affinities to remipeds found on both sides of the North Atlantic. Speciation has resulted from their isolation in widely separated habitats. A blind gudgeon and an eel are found throughout the water profile.

Sources & Further reading

Mary E. White, Earth Alive, From Microbes to a Living Planet, Rosenberg Publishing Pty. Ltd., 2003