Australia’s Nice Barrier Reef may by no means have come to be have been it not for the formation of an unlimited island based mostly totally on sand.
Okay’gari, also referred to as Fraser Island, has the honour of being the world’s largest sand island, protecting round 640 sq. miles (practically 1,700 sq. kilometers) simply off the southeastern coast of Queensland.
Together with the close by Cooloola Sand Mass, the mass of forested dunes and seashores types an unofficial base to the huge reef that sits to its north.
If this terrestrial ‘launching pad’ had by no means shaped, researchers assume the plenty of sand carried northwards alongside the coast by ocean currents would have landed proper the place the reef now sits.
Quartz-rich sands have a approach of smothering carbonate-rich sediments, that are obligatory for coral improvement.
With out Okay’gari in the best way to information sediment off the continental shelf and into the deep, situations wouldn’t have suited the formation of the world’s largest coral reef, consultants argue.
The Nice Barrier Reef has a complicated origin story. It solely shaped half one million years in the past, lengthy after situations have been acceptable for the expansion of coral.
Okay’gari could be the misplaced puzzle piece researchers have been trying to find. Evaluation and relationship of sand from the numerous dunes on the 123 kilometer (76 mile) lengthy island recommend the land mass shaped between 1.2 and 0.7 million years in the past, only a few hundred thousand years earlier than the Nice Barrier Reef got here to be.
The island’s presence in all probability deflected northward currents, researchers clarify, offering the southern and central components of the good barrier reef the reprieve they wanted to begin rising hundreds of kilometers of coral.
Okay’gari and Cooloola themselves arose from the buildup of sand and sediment from the south.
Amid durations of ice formation and fluctuating sea ranges, researchers suspect sediment around the globe ‘all of a sudden’ turned uncovered. In successive durations of ice soften and rising oceans, that sediment then received caught up within the currents.
Alongside the east coast of Australia this in all probability meant an extended northward treadmill of soil and sand tracing the continental shelf.
A slope off the southern coast of Queensland, nevertheless, makes the right place for sediment to build up, and that is proper the place Okay’gari and Cooloola are discovered.
Simply south of the sand plenty, coral reefs are conspicuously lacking.
If researchers are proper, that is in all probability as a result of the northward currents listed below are too sturdy. Okay’gari and Cooloola break up the lengthy distance dispersal, stopping quartz-rich sands from smothering growing reefs.
“Earlier than Fraser Island developed, northward longshore transport would have interfered with coral reef improvement within the southern and central [Great Barrier Reef],” researchers write.
Sediment information from the southern Nice Barrier Reef assist this concept. About 700,000 years in the past, there seems to have been an uptick in carbonate content material in sediment on this area.
Analysis on reefs additional north is now wanted as nicely, however a minimum of two-thirds of the Nice Barrier Reef appears to owe its existence to a wall of sand to the south.
“The event of Fraser Island dramatically lowered sediment provide to the continental shelf north of the island,” the authors argue.
“This facilitated widespread coral reef formation within the southern and central Nice Barrier Reef and was a obligatory precondition for its improvement.”
The examine was revealed in Nature Geoscience.