Coral fossils reveal 600,000 years of hidden climate records

The story of our planet lies hidden in unexpected places. Among them, coral fossils serve as delicate time capsules, recording the rise and fall of ancient seas.

Now, a breakthrough by a University of Sydney Ph.D. student promises to unlock those long-lost records with remarkable precision.

Carra Williams, working with the Australian Nuclear Science and Technology Organisation (ANSTO), used neutron computed tomography (NCT) to study coral fossils in three dimensions.

The study reveals fine details within the coral’s structure without damaging it, offering a fresh window into Earth’s climate history.

“This method opens the door to recovering climate information from coral samples once written off as too altered to be useful,” said Williams.

Coral fossils hold climate clues

Corals build skeletons from aragonite, a mineral that gradually transforms into calcite over time. This natural change often erases critical chemical information about the ocean’s temperature and chemistry when the coral grew.

Such degradation has long made ancient corals unreliable for reconstructing past climates.

Williams and her team used neutron computed tomography at ANSTO’s DINGO imaging instrument to locate surviving pockets of original aragonite inside damaged fossils.

These preserved sections carry the chemical signals that reveal sea-level changes and ocean conditions stretching back hundreds of thousands of years.

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

Hidden signals in old corals

In simple terms, NCT directs beams of neutrons from ANSTO’s OPAL research reactor through coral fossils, creating detailed internal images much like medical CT scans. These images expose hidden mineral structures that X-rays cannot detect.

The scans revealed untouched aragonite zones inside fossils thought too weathered for study. “This is like finding intact pages in an otherwise weathered book,” said Williams.

“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.”

Her findings show that even corals once considered useless can still provide crucial climate data, helping scientists assess how today’s reefs might react to modern warming and sea-level rise.

Rewriting reef history with neutrons

Professor Jody Webster, an expert on coral reef history, supervised the project. He believes the technique could change how scientists reconstruct ancient climates.

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

This marks the first time NCT has been used to screen fossil corals for climate and dating studies. Unlike X-rays, neutrons are particularly sensitive to hydrogen, allowing precise identification of aragonite, which holds more water and organic matter than calcite.

The technique provides a clear three-dimensional mineral map without cutting the coral open.

Tracing 600,000 years of coral reefs

The study examined four coral samples. These included a modern coral from One Tree Reef at the University of Sydney’s research station on One Tree Island.

The team also studied three fossils: one from Muschu Island in Papua New Guinea dated to about 1,650 years ago, another from the Late Pleistocene at Ashmore Reef more than 40,000 years old, and a Mid-Pleistocene specimen from the Great Barrier Reef around 600,000 years old.

The findings, published in Geochemistry, Geophysics, Geosystems by the American Geophysical Union, mark an important collaboration between the University of Sydney and ANSTO.

The work demonstrates the power of combining advanced nuclear imaging with Earth science to uncover hidden histories. Through the eyes of neutrons, the silent fossils of ancient reefs are speaking again.

Each coral skeleton becomes a storyteller, revealing how oceans shifted, warmed, and adapted over ages. Williams’s research does more than read the past; it gives humanity the knowledge to face what lies ahead.

Past reefs guide future oceans

Understanding ancient reefs goes beyond curiosity. These fossils reveal how ecosystems responded to natural warming and cooling over millennia.

That context helps scientists model today’s rapid changes with greater accuracy. If corals once survived gradual shifts in sea temperature, can they withstand the sudden pace of human-driven climate change?

The data extracted through NCT could strengthen climate models that guide conservation efforts.

It pinpoints periods when reefs collapsed or rebounded, offering valuable lessons for restoration strategies today. Coral records might even help forecast ocean acidification and its long-term effects on marine biodiversity.

Expanding the reach of neutrons

The potential applications of this technology extend well beyond coral research. Archaeologists, paleontologists, and materials scientists can use NCT to examine delicate samples without destroying them.

For geoscientists, it opens new opportunities to explore fossils once thought too degraded for meaningful study.

Williams hopes the technique will become a standard tool in paleoclimate research. She plans to refine the imaging process to detect even smaller patches of aragonite in highly altered corals.

Her vision reflects a growing scientific movement: using non-invasive imaging to preserve and interpret the fragile record of Earth’s history.

Coral fossils connect past and future

This collaboration between the University of Sydney and ANSTO shows how curiosity-driven research can reshape understanding.

The project bridges generations of geological time, connecting the fossilized whispers of ancient reefs to the urgent voices of climate scientists today.

By revealing what lies beneath the surface, Williams has offered science a new lens. Her work reminds us that even the most weathered pages of Earth’s story still hold lines waiting to be read.

The study is published in the journal Geochemistry Geophysics Geosystems.

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