Media release

From: The University of Sydney

A University of Sydney student has developed a completely new way to peer inside coral fossils to recover lost records of past climate change.

In collaboration with the Australian Nuclear Science and Technology Organisation (ANSTO), geoscientist Carra Williams has pioneered the use of neutron computed tomography (NCT) to identify tiny, well-preserved pockets of coral skeleton that can reveal precise timelines of sea-level and climate shifts stretching back hundreds of thousands of years.

“This method opens the door to recovering climate information from coral samples once written off as too altered to be useful,” said Ms Williams, who is undertaking a PhD in the University of Sydney’s School of Geosciences in the Geocoastal Research Group.

“By seeing inside the fossils in 3D, we can distinguish the original coral mineral, aragonite, from its altered form, calcite. The aragonite retains the best signals of past ocean and climate conditions in coral that are available to us.”

Ms Williams said that by understanding the past with greater detail, we are best prepared to understand how anthropogenic climate change will affect reefs today and in the future.

CORAL SKELETONS AND WEATHERED BOOKS

Corals build their skeletons from aragonite, a form of calcium carbonate. Over time, this delicate mineral often transforms into calcite through a process called diagenesis, destroying much of the original information about the climate when the coral was growing, rendering fossils unreliable for dating and reconstructing past climates.

By harnessing neutron computed tomography at ANSTO’s DINGO neutron imaging instrument, the Sydney team was able to scan coral cores and map where aragonite survives inside altered specimens, without damaging the samples.

In simplified terms NCT involves directing beams of neutrons – produced at ANSTO’s OPAL research reactor at Lucas Heights – through the coral fossils to create images of their internal structures, much like X-rays or CT scans are used to look inside the human body.

The scans revealed hidden aragonite zones, proving that even previously “undateable” fossils can still yield robust information.

“This is like finding intact pages in an otherwise weathered book,” Ms Williams said.

“Those rare sections of original aragonite allow us to extend and strengthen our records of how reefs and oceans responded to major environmental changes in the past. That context is critical for assessing how today’s reefs will cope with rapid warming and sea-level rise.”

The project is supervised by Professor Jody Webster, a global authority on coral reef history. He said the new approach has the potential to transform how scientists reconstruct the records of ancient climates.

“Coral reefs are one of the most sensitive archives of environmental change,” Professor Webster said.

“By using neutrons to look inside their fossils, we can unlock data that has been hidden for millennia. This will help us understand the thresholds and tipping points reefs faced in the past – vital knowledge as human-driven climate change accelerates.”

The research demonstrates the first use of NCT to screen fossil corals for climate and dating studies. Unlike X-rays, which show only density contrasts, neutrons are highly sensitive to hydrogen, making them ideal for detecting aragonite, which holds more water and organic matter than calcite.

The result is a clear 3D map of mineral phases inside a coral core without cutting it open.

The study analysed four coral samples, including a calibration sample of modern coral from One Tree Reef at the University of Sydney’s research station at One Tree Island. The geologic samples included a recent fossil from Muschu Island in Papua New Guinea from about 1650 years ago, a Late-Pleistocene era sample more than 40,000 years old from Ashmore Reef on the Northwest Shelf, and a fossilised Mid-Pleistocene era sample from the Great Barrier Reef that is about 600,000 years old.

The research has been published in Geochemistry, Geophysics, Geosystems of the American Geophysical Union. The study marks an important collaboration between the University of Sydney and ANSTO, Australia’s nuclear science agency.

The work highlights the University of Sydney as a place where students can lead world-first discoveries with global impact.

“It’s exciting to see a PhD student driving such innovative science,” Professor Webster said. “Carra’s work shows the calibre of research training we offer – combining cutting-edge technology with big questions about humanity’s future.”

Download videos of coral scanning and photos of the researchers at this link.

Research

Williams, C. et al ‘Neutron computed tomography: a novel high-resolution, non-destructive method for screening fossil coral for diagenetic alteration for geochronologic and paleoclimatic reconstructions’ (Geochemistry, Geophysics, Geosystems 2005).
DOI: 10.1029/2025GC012439

Declaration

The authors declare no competing interests. Funding sources included the Australian Research Council, the Australian Institute of Nuclear Science and Engineering, and the University of Sydney. The authors acknowledge the support and access to ANSTO facilities.