Analysis of fossilized corals from the Great Barrier Reef reveal that it suffered five deaths in the past 30,000 years but was able to resurrect itself each time.
In a study, a team of scientists found that the Great Barrier Reef adjusted to drastic changes in sea level through migrating to the sea and landward again. Specifically, the reef was able to migrate laterally at between 0.2 and 1.5 meters a year to accommodate the rising and falling of the ocean levels in the past.
Each time it dies due to environmental swings, the Great Barrier Reef stayed resilient by shifting, growing, and evolving with the ocean. Hence, coralline-algae and other corals continue to thrive in the reef's ecosystem.
The team of international scientists who mapped this process of resurrection, however, believed that the world's largest reef may no longer survive a sixth impending death that could happen within the next millennia. It may no longer be able to keep pace with the rate of climate change at present.
Great Barrier Reef Dead
The team, led by Jody Webster from the University of Sydney, recreated how the Great Barrier Reef evolved over the past 30 millennia amid major changes in the environment.
They employed data from geomorphic, sedimentological, biological, and dating information from the fossilized reef at 16 sites at Cairns and Mackay. Their study, published in Nature Geoscience, looked into the period from pre-Last Glacial Maximum that happened about 30,000 to 22,000 years ago.
At that time, sea levels were 118 meters below the current levels and continued to drop during the following periods. The Great Barrier Reef died twice within this interlude because of subaerial exposure or being exposed to atmosphere present in drylands. The reef came back to life by moving seaward as sea levels fall.
The Great Barrier Reef died twice again within the deglaciation period that took place subsequent to the Last Glacial Maximum. The deaths occurred at about 17,000 and 13,000 years ago. At the time, the reef died due to rapid rising of sea levels. That time, the reef breathed new life into its ecosystem again by moving landward.
The fifth death occurred about 10,000 years ago. The cause of death at the time, however, was no longer the rise and falls of sea levels alone but also because of simultaneous sedimentary increase and degrading water quality — a trio that has been rapidly happening at present due to climate change.
The Future Of The Great Barrier Reef
Webster and his team noted that while the Great Barrier Reef has been resilient to sea level changes in the past, it was extra vulnerable to sedimentary deposits. The latter becomes of greater concern since industrial land abuse is accelerating the accumulation of sediments in the ocean.
"Our study shows that as well as responding to sea-level changes, the reef has been particularly sensitive to sediment fluxes in the past and that means, in the current period, we need to understand how practices from primary industry are affecting sediment input and water quality on the reef," Webster explained.
On top of concerns about land use, other studies showed that sea surface temperature is already changing at a rate of 0.7 degrees in a century. With the current coral conditions in the Great Barrier Reef, the team surmised that it will no longer be as resilient as it had been in the past and may not be capable of keeping paced with accelerated environmental swings at present.