Several reports and studies have gone into detail about how Australia's Great Barrier Reef is dying, as bleaching and warmer water temperatures continue to affect the system's corals. While a new study suggests that the reef had come close to dying five times in the last 30,000 years, the researchers behind the paper also warned that the stresses that are threatening the system are far more significant than they were during those near-extinction periods.
As detailed in a study published in the journal Nature Geoscience, a multinational team of researchers extended their observations beyond what currently makes up the Great Barrier Reef to see how close it was to death on repeated occasions over the past several thousands of years. According to Newsweek, the researchers looked for places where coral might have grown in ancient times, then gathered coral fossils and sediments dating back up to 30,000 years ago after drilling into the seafloor.
According to the researchers' findings, low sea levels were the reason why the Great Barrier Reef was close to dying 30,000 years and 22,000 years ago, in the aftermath of the last Ice Age, as air exposure caused corals to die out, with the remaining reefs changing their position and surviving what had turned out to be a close call for the entire system. Rising sea levels, on the other hand, caused massive amounts of coral to die between 13,000 and 17,000 years ago in two separate events, but in those two instances, the coral migrated closer to land.
A combination of factors led to the reef's fifth and final mass coral die-off, as the researchers cited poor water quality, rising sea levels, and an overflow of sediment as the reasons behind the event, which is estimated to have taken place about 10,000 years ago. With all the migrations that took place as the Great Barrier Reef tried to survive the die-offs, the team believes that its modern incarnation firmed up approximately 9,000 years ago.
Looking at the current situation, where coral bleaching is a major cause for concern for those trying to save the Great Barrier Reef, study lead author and University of Sydney researcher Jody Webster said that he has "great concerns" about how the reef could survive in its present state due to the intensity of the stresses it is facing and may likely face in the near future.National Oceanic and Atmospheric Administration coral reef ecologist Mark Eakin, who did not take part in the study, said that the Great Barrier Reef's die-offs from ancient times are similar to how things are in modern times. But instead of fluctuating sea levels, warmer water temperatures have been largely responsible for the stresses the reef is experiencing, as heat waves have led to severe coral bleaching.
"Don't expect reefs to be able to bounce back quickly," Eakin told Science magazine.
Although Webster did not say that the present situation at the Great Barrier Reef will immediately lead to a similar die-off to what it went through historically, he said that such an event might take place "sometime in the next few thousand years," according to Newsweek. It isn't clear whether man-made climate change will cause the event to take place sooner than expected, but Webster noted that his timeline might be accurate if the reef "follows its past geological pattern."