Extensive Relict Coral Reef Found

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Coral reefs are sensitive to climate change and track sea level. New observations show that an extensive coral reef existed in the southern Pacific Ocean thousands of years ago.

Woodroffe et al. used multi-beam sonar, coring, and dating to examine a relict reef discovered in water about 20-25 meters (65-82 feet) deep around Lord Howe Island in the southern Pacific Ocean.

They found that the reef thrived from about 9,000 to 7,000 years ago and covered an area 20 times larger than the modern reef, which is the southernmost Pacific coral reef.

About 7,000 years ago, the reef was drowned, probably due to abrupt sea level rise, and then shrunk to its modern extent.

The observation shows the extent to which reefs grew 9,000 years ago. Today coral reefs exist mainly in shallow seawater with sea surface temperatures greater than 18 degrees Celsius (64 degrees Fahrenheit), at latitudes near the equator.

The relict reef shows that corals previously existed at southern latitudes farther from the equator.

The researchers note that as ocean temperatures warm due to climate change, the relict reef could become a substrate for new coral reef growth.

Authors of the study include: Colin D. Woodroffe, Michelle Linklater, Brian G. Jones: School of Earth and Environmental Sciences, University of Wollongong, Wollongong, New South Wales, Australia; Brendan P. Brooke, Cameron Buchanan, Richard Mleczko: Geoscience Australia, Canberra, ACT, Australia; David M. Kennedy, School of Geography, Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand; Quan Hua, Australian Nuclear Science and Technology Organization, Kirrawee, New South Wales, Australia; Jian-xin Zhao, Radiogenic Isotope Facility, Centre for Microscopy and Microanalysis, University of Queensland, Brisbane, Queensland, Australia.