The glue that holds the Great Barrier Reef together becomes thinner and weaker as oceans become more acidic, a study shows.
University of Sydney geoscientists measured more than 700 microbialite samples - calcified deposits from microbes that live within reef formations - and compared them with reef records from around the world.
In reefs like the Great Barrier Reef microbialite crusts formed through bacteria and then bind to the reef, creating scaffolds used by corals to grow.
The study suggests that climate change driven changes to dissolved carbon dioxide, pH and temperature could result in less crusts forming, resulting in weakened reef frameworks.
School of Geosciences associate professor Jody Webster says the microbialites are a good indicator of changes in environmental conditions of oceans.
"This geologic study shows that as oceans became more acidic, this is reflected in the thickness of these reef crusts," he said.
"The findings are a stark warning sign for the dangers of rapid acidification of oceans."
The study showed the microbialite crusts were 11.5 centimetres thick 22,500 years ago, reducing to about 3cm in younger parts of the Great Barrier Reef 12,000 years ago.
Paired with worldwide reef studies, the figures showed the thinning coincided with pH levels dropping below 8.2 up to modern times.