Great Barrier Reef Fossils to Reveal Past Sea Levels

By harvesting coral fossils that are more than 20,000 years old, experts hope to be able to paint a clearer picture of how global sea levels may have changed over time, and especially since the last glacial period.

A team of researchers recently conducted an expedition at the outer fringes of the Great Barrier Reef, in Australia, and managed to collect samples of organisms that lived more than 20 millennia ago.

This fossilized ancestor of the modern ecosystem was alive at a time when North America was covered in a thick layer of ice, and when global temperatures were 5 degrees Celsius lower than the are today.

The thing about the newly-collected samples is that they could finally provide researchers with an accurate image of how sea levels evolved over the past few thousand of years. Any changes should be inscribed in these fossilized remains.

According to the team behind this investigation, the data derived from studying the fossilized corals may also help inform more accurate prediction models, that currently seek to make sense of how sea levels will look like in the future.

The research vessel Greatship Maya was used for this research, which involved the science team looking for the coral fossils on and below the ocean floor, at the extremities of the Great Barrier Reef.

The vessel featured a massive drilling rig, and it spent the better part of two months boring holes at three locations of interest in the massive reef. The goal was to obtain so-called cylindrical samples.

These are cylindrical, tube-like stretches of material, which go deep into the planet's crust. In all, the researchers collected more than 225 meters (730 feet) of such coral samples.

The project was supported by the Integrated Ocean Drilling Program (IODP), and the European Consortium for Research Drilling (ECORD), two multinational research institutions.

According to staff scientists Carol Cotterill, the Great Barrier Reef was selected for this study because it was not subjected to tectonic activities over the years. At other locations where coral reefs exist, tremors and earthquakes changed the ecosystems' properties beyond recognition.

But the Australian Reef stayed put over the years, at least in the past 20 millennia. “We don't have a separate signal to distract us, so we're fairly confident that what we have here are really the global sea-level changes,” argues Cotterill.

"Some species grow in bands, like tree rings, and as they grow they have to extract certain things from the water to form the skeletons, so you get that chemical signature trapped within each of the bands,” says the expert, quoted by OurAmazingPlanet.

Corals can keep track of oceanic properties including salinity, chemistry, temperatures and even levels. Changes in either of these factors are inscribed in their calcium-carbonate skeletons.