Exposure of corals to air caused two widespread "death events", roughly 30,000 and 22,000 years ago. Two others – 17,000 and 13,000 years ago – were triggered by rapid sea-level rise as disintegrating ice sheets and glaciers triggered "meltwater pulses".

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A fifth abrupt decline in corals appears to coincide with a jump in sediment levels as sea levels rose about 9000 years ago. Scientists "are still working on the smoking gun" for that event, which may have been caused by an increase in precipitation and floods, Professor Webster said.

No 'beacon of hope'

While the research revealed the past dynamism of the reef, the paper stressed the findings "provide little evidence for resilience of the Great Barrier Reef over the next few decades".

That's because the pace of temperature increases has been much greater in the past century, at about 0.7 degrees, compared with "a couple of degrees rise in a 10,000-year period", Professor Webster said.

“I would not hold up this study as a beacon of hope in terms of how the reef might respond in the next 20, 50, 100 years," he said.

Tom Bridge, a research fellow at the ARC Centre of Excellence for Coral Reef Studies and the Queensland Museum Network, said the research was an important addition to our understanding of the reef's history.

"We think of something like the reef as being big, that it’s always been there, and always will be there,” Dr Bridge said, adding this research showed "it is a really dynamic system, but also the magnitude of how rapidly it can change”.

The unprecedented back-to-back bleaching that killed half the reef's corals over the 2015-16 and 2016-17 summers underscored how vulnerable the corals were to "really anomalous" temperatures that can be masked by rising averages, Dr Bridge said.

Apart from reducing the threat from rapid climate change through reducing greenhouse gas emissions, governments can continue to assist the health of the reef by limiting sediment from land-clearing and other sources.

“If you can preserve parts of it and minimise the damage, over longer time-scales you can help it re-establish as it has done in the past," Dr Bridge said. "We need to make sure the conditions are there [for the reef] to recover."

The work, made possible by $10 million in funding from the International Ocean Drilling Program, had already generated published research on temperature changes. A third paper, expected to be published soon, will examine the link between sea-level changes and ice sheet dynamics, Professor Webster said.