Fossil evidence shows how the great barrier reef could endure rising seas

The Future of the Great Barrier Reef: Lessons from Ancient Coral Cores (Image: Canva)

Scientists from the University of Sydney have illuminated the issues for the Great Barrier Reef. They studied how the reef may adapt to sea level rise due to global warming. The results give us a better indication of what the future might bring to this natural phenomenon.

How the Reef Responded to Past Sea Level Changes
The research, from Professor Jody Webster of the School of Geosciences, has been published today in Nature Communications. It is based on fossil reef cores extracted from under the seabed of the Great Barrier Reef. These cores are like a geological time capsule, revealing how the earlier forms of the reef responded to change thousands of years ago.

The researchers concentrated on a time of approximately 10,000 years ago when there was a reef called Reef 4. Only a quick rise in sea level would not result in the death of Reef 4. Rather, the reef was dying because of other stresses such as heating waters and low-quality water. These accumulated stresses ultimately killed it at the close of the last ice age.

During the next one to two millennia, Reef 4 moved inshore and built up into the Great Barrier Reef that we know today. "A healthy reef is able to build up even in the face of rapid sea level rise," according to Professor Webster. "It's the interaction of stresses that leads to problems."

A Closer Look at Meltwater Pulse 1B
The scientists analysed cores 13,000 to 10,000 years old. They focused on Meltwater Pulse 1B, which was a 350-year period of fast sea level increase between 11,450 and 11,100 years ago. In this period, polar ice sheets melted more quickly than they normally did under warming.

Previous research indicated sea levels increased approximately 40 millimetres per year over this time. The new analysis indicates the increase was much more gradual — three to five millimetres annually, comparable to current rates. This contradicts previous hypotheses and provides critical background to modern developments.

The cores were drilled from 40 to 50 metres below the reef shelf edge. Reef 4 had a similar mix of corals and algae as the modern reef, with comparable growth patterns. This makes studying its history highly relevant for understanding today’s reef challenges.

What This Means for Today’s Great Barrier Reef
Today's Great Barrier Reef is under numerous threats such as sea level rise, heatwaves, bleaching, and rising pollution. Professor Webster cautions that these combined stresses are concerning. "The reef may survive but will probably be changed in the future," he said. "We may have fewer coral species and less complex structures.

The fossil cores, collected under the International Ocean Discovery Program (IODP), yield critical data extending much beyond the 50 to 100 years accessible with contemporary equipment. This extended perspective informs researchers about how reefs have responded to previous environmental changes.

Professor Webster collaborated with universities of Tokyo, Australian National University, Nagoya University, Granada University, and Aix-Marseille University. Their synergy highlights the importance of global collaboration in addressing climate issues.

This study gives a multifaceted portrait of the Great Barrier Reef's history and future. It shows the resilience of the reef but also the threats from several environmental pressures. Awareness of this balance will be the key to preserving the reef for the next generation.