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Reef Survived Last Ice Age

The Great Barrier Reef grew during the last ice age, even though the water temperatures were 4–5°C colder than today, according to research published in Nature Communications. “It was right at the colder limit of what corals can take, but the reef grew and developed from there,” said Dr Helen McGregor of the Australian National University.

The research helps scientists better understand the resilience of the world-heritage listed Great Barrier Reef and how it copes with changing ocean temperatures.

“The corals survived a gradual temperature rise from 20,000 to 12,000 years ago. However we don’t know if the reef will survive that change over the next 100 years,” McGregor said. “We do know that if summer temperature extremes occur more frequently, then corals are likely to bleach more regularly.”

McGregor is part of the Integrated Ocean Discovery Program climate team, which drilled cores from the reef near Cairns and Mackay. The historical record of the chemical make-up of the coral at the different locations has enabled the international team to reconstruct ocean temperatures since the last ice age.

The Coral Sea experienced lower temperatures and a large temperature gradient between Cairns and Mackay, which likely influenced the weather patterns in the region significantly. “Our results suggest the eastern Australian current was not bringing warmer water down the coast like it does today,” McGregor said. “The cooler waters point to less monsoonal rainfall in Queensland, something that’s been observed by other measurements but we haven’t been able to explain before.”