(ORDO NEWS) — Australia’s Great Barrier Reef might never have formed had it not been for the formation of a huge island made up mostly of sand.
The island was previously called Kgari (K`gari), which in the language of Batchulla meant “paradise”. Its modern name, Fraser Island, is associated with the name of Captain Fraser and his wife, whose ship “Stirling Castle” was wrecked on the island.
It is the world’s largest sand island, covering approximately 1,700 square kilometers, off the southeast coast of Queensland.
Together with the nearby Kulula sandy massif, wooded dunes and beaches form the informal backbone of the huge reef to the north.
Scientists believe that if this land-based “launching pad” had never been built, the masses of sand carried north along the coast by ocean currents would have ended up exactly where the reef is now.
And sands rich in quartz can suppress the carbonate-rich deposits needed for coral development.
Experts say that without Fraser Island’s ability to drain sediment from the continental shelf into the hinterland, the conditions for the world’s largest coral reef would be unsuitable.
The Great Barrier Reef has a complicated history. It formed only half a million years ago, long after the conditions for coral development became favorable.
Kgari may have been the lost piece of the puzzle the researchers were looking for. Analysis and dating of sand from several dunes on the 123-kilometer-long island suggests that the landmass formed between 1.2 and 0.7 million years ago, just a few hundred thousand years before the Great Barrier Reef.
The researchers explain that the presence of the island likely diverted the currents to the north, giving the southern and central portions of the large coral reef the calm they needed to grow thousands of miles of coral.
Scientists suspect that during periods of ice formation and sea level fluctuations, sediments around the world were “suddenly” exposed. During subsequent periods of ice melt and sea level rise, sediment was carried by currents.
Along the east coast of Australia, this probably meant a long stride north over land and sand, tracing the continental shelf.
However, the slope off the south coast of Queensland is an ideal place for sediment accumulation, and it is here that large sandy islands are located. There are clearly no coral reefs south of the sandy masses.
If the scientists are right, it is probably because the northern currents are too strong here. Islands prevent settlement over long distances by preventing quartz-rich sand from clogging developing reefs.
Prior to the development of Fraser Island, coastal transport to the north disrupted the development of the southern and central coral reefs of the Great Barrier Reef, the scientists explained.
And the sedimentary records of the southern Great Barrier Reef support this idea. Apparently, about 700,000 years ago, a sharp increase in the content of carbonates in sedimentary rocks occurred in this region.
Research is now needed on reefs further north, but at least two-thirds of the Great Barrier Reef appears to owe its existence to the sand wall to the south.
“The development of Fraser Island has drastically reduced sediment supply to the continental shelf north of the island,” the authors say.
“This contributed to the widespread formation of coral reefs in the southern and central parts of the Great Barrier Reef and was a necessary condition for its development.”
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