The world’s largest sand island formed around a million years ago and enabled the southern and central Great Barrier Reef to develop, new research suggests.
An international team of scientists have dated K’gari (Fraser Island) and the nearby Cooloola Sand Mass in south-east Queensland as forming between 0.7m and 1.2m years ago.
Their formation was “a necessary precondition for initiation of the southern and central Great Barrier Reef”, the researchers found.
In geological terms, the world’s largest reef system developed relatively recently – an estimated 450,000 to 670,000 years ago.
The study’s authors described this timing as a “conundrum”, because climatic conditions along the central and southern Queensland coastline have been ideal for reef growth since much earlier – between 2.6m years and 5.3m years ago, during the Pliocene epoch.
Study co-author Prof Patrick Moss, head of the school of earth and environmental sciences at the University of Queensland, said there were two main theories for the formation of the Great Barrier Reef.
The first is temperature – “that basically from around 500,000 … [to] 700,000 years ago, there was a 4C increase in sea surface temperatures which allowed reef growth to occur,” Moss said.
The second theory, which the K’gari study supports, is that clear waters were necessary.
“Before K’gari and the other giant sand masses were formed, you had a lot more sand transport further north, and so that would produce murkier water and limit reef growth at that time,” Moss said.
K’gari, a Unesco world heritage site, is the world’s largest sand island and also the end point of one of the world’s longest “longshore drift” coastal systems. Sand from the island originates as far as central New South Wales, travelling 1,500km north along the east coast of Australia.
“The longshore drift process picks up sand grains and transports them to K’gari and along the Gold Coast and Sunshine Coast,” Moss said. “That’s a really important aspect of creating south-east Queensland environment.”
K’gari and the dune fields acted as a barrier to this longshore drift process, enabling reef growth, the study’s authors suggest.
The researchers dated the age of the dunes on K’gari using two techniques: optically stimulated luminescence and palaeomagnetic dating.
Optically stimulated luminescence involves agitating sand grains and measuring the wavelengths of light they emit.
“Sand grains, when they’re buried, trap electrons in their lattice,” Moss said. “The longer it’s buried, the more electrons you have in the structure of the sand grains.”
Paleomagnetic dating is a technique that yields the age of a rock based on changes over time in the orientation of the Earth’s magnetic field.
Fraser Island is in the process of having its name reinstated as K’gari, which means paradise in the Butchulla language.
“The name Fraser Island is culturally inappropriate,” the Queensland environment minister, Meaghan Scanlon, said earlier this year.
“It is a tribute to Eliza Fraser, a woman whose narrative directly led to the massacre and dispossession of the Butchulla people.”
The first author of the study, published in the journal Nature Geoscience, is Dr Daniel Ellerton of Stockholm University.
