Mysterious origins of the Great Barrier Reef could finally be explained: ScienceAlert

Australia’s Great Barrier Reef might never have come into existence if not for the formation of a vast island based primarily on sand.

K’gari, also known as Fraser Island, holds the honor of being the largest sand island in the world, covering approximately 640 square miles (nearly 1,700 square kilometers) just off the south coast. East Queensland.

Together with the nearby Cooloola sand mass, the mass of wooded dunes and beaches form an unofficial base of the vast reef that lies to the north.

If this land-based “launch pad” had never formed, the researchers believe that sand masses carried north along the coast by ocean currents would have landed where the reef currently stands.

Quartz-rich sands have a way of smothering carbonate-rich sediments, which are necessary for coral development.

Without K’gari to guide sediment from the continental shelf to the depths, conditions would not have been conducive to the formation of the world’s largest coral reef, experts say.

The Great Barrier Reef has a confusing origin story. It only formed half a million years ago, long after conditions were right for coral growth.

K’gari might be the lost puzzle piece researchers have been looking for. Analysis and dating of sand from the many dunes on the 123 kilometer (76 mile) long island suggests the landmass was formed between 1.2 and 0.7 million years ago, a few hundred thousands of years before the creation of the Great Barrier Reef.

The island’s presence likely diverted the currents north, the researchers say, giving the southern and central parts of the Great Barrier Reef the breathing space they needed to start farming thousands of miles of coral.

Deviation of K'gari Coast Sediment
The coast of Queensland, Australia, showing the dispersion of sediment before the formation of K’gari and Cooloola (left) and after (right). (Ellerton et al., Nature Geoscience, 2022)

K’gari and Cooloola themselves were born from the accumulation of sand and sediment from the south.

Amid periods of ice formation and fluctuating sea levels, researchers suspect that sediments around the world have been “suddenly” exposed. During successive periods of melting ice and rising oceans, these sediments were then carried away by the currents.

Along the east coast of Australia this probably meant a long northerly conveyor belt of soil and sand tracing the continental shelf.

A slope off the southern coast of Queensland, however, provides the ideal location for sediment accumulation, and this is where K’gari and Cooloola are found.

Just south of the sand masses, coral reefs are conspicuously lacking.

If the researchers are right, it’s probably because the northward currents here are too strong. K’gari and Cooloola break up dispersal over long distances, preventing quartz-rich sands from smothering developing reefs.

“Before the development of Fraser Island, northward coastal transport would have interfered with the development of coral reefs in the south and central [Great Barrier Reef],” researchers write.

Sediment records from the southern Great Barrier Reef support this idea. About 700,000 years ago there appears to have been a slight increase in carbonate content in the sediments of this region.

Research on the reefs further north is also needed, but at least two-thirds of the Great Barrier Reef seems to owe its existence to a wall of sand to the south.

“The development of Fraser Island has significantly reduced the supply of sediment to the continental shelf north of the island,” explain the authors. Argue.

“This facilitated the widespread formation of coral reefs in the southern and central Great Barrier Reef and was a necessary prerequisite for its development.”

The study was published in nature geoscience.

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