Great Barrier Reef's Survived at Least 5 'Death Events' Before

Cristina Cross
May 31, 2018

Two of what the scientists dubbed death events happened 30,000 and 22,000 years ago and were caused by subaerial exposure, which is when the reef becomes exposed to air.

The Great Barrier Reef has survived five death events in 30,000 years, but research says modern times may be pushing it past its breaking point.

The authors emphasize in their paper that the findings do not suggest that the reef will be able to resist today's rapid environmental change, writing, "Given the current rate of [sea-surface temperature] increase (0.7°C per 100 years), sharp declines in coral coverage, and the potential for year-on-year mass coral bleaching, our new findings provide little evidence for resilience of the [Great Barrier Reef] over the next few decades".

However, on several occasions the reef apparently did not respond fast enough to environmental change.

The latest study documenting the near-misses of the Great Barrier Reef's coral was published this week in the journal Nature Geoscience. During sea level drops, for instance, the Great Barrier Reef as a whole survived by migrating towards deeper waters, and marching back towards land as the level rose again.

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The study used data from fossil reef cores at 16 sites at Cairns and Mackay in Queensland, according to a statement from the university. The reefs either shifted landward or seaward in correspondence with the ocean's falling or rising level.

"I have grave concerns about the ability of the reef in its current form to survive the pace of change caused by the many current stresses and those projected into the near future", Webster said, noting that the rate of sea surface temperature rise and sediment flux increase has exceeded the speed of coral recovery. During this timeframe, there were at least five really close calls due to all sorts of threats, such as sea level rises, temperature swings, and sediment increases. The last death event reportedly took place near about ten thousand years ago.

Two more death events occurred at the deglaciation period 17,000 and 13,000 years ago, this time brought about by the sea levels rising rapidly. The most recent, which occurred around 10,000 years ago, was associated with a decline in water quality and increase in sediment.

The fact that the reef persisted through these events showed the researchers that it's more resilient in the face of danger than was previously thought. Jody M. Webster, Juan Carlos Braga, Marc Humblet, Donald C. Potts, Yasufumi Iryu, Yusuke Yokoyama, Kazuhiko Fujita, Raphael Bourillot, Tezer M. Esat, Stewart Fallon, William G. Thompson, Alexander L. Thomas, Hironobu Kan, Helen V. McGregor, Gustavo Hinestrosa, Stephen P. Obrochta & Bryan C. Lougheed.

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