The pristine tropical waters off Raine Island in the far northern Great Barrier Reef are inviting in the warmer months, and not only for sea life. John Dawson, PhD candidate from the School of Earth and Environmental Sciences at Queensland's James Cook University, will be afloat in the shallower parts again in November.
Together with Dr Quan Hua, Senior Research Scientist at the ANSTO Institute for Environmental Research, John is using Accelerator Mass Spectrometry (AMS) dating techniques at ANSTO's accelerator facilities to analyse sediment of low-lying reef islands.
Quan explains that their research centres on the study of skeletal components in sediment like coral, coralline algae, molluscs, and the naturally-occurring carbon-14 (C-14) radioisotope in each layer. Analysis of the specimens is undertaken using ANSTO's ANTARES and STAR accelerators.
By studying the sediment, scientists are able to find out the age of the particular layer, examine patterns of sediment production and more accurately determine the growth rates of reef islands.
This research will enable an improved understanding of the environmental change in tropical marine ecosystems and will help marine authorities in implementing a sustainable management framework for the Great Barrier Reef.
"John is measuring and charting carbonate purchase from the skeletal remains of small reef organisms called foraminifera (forams), around 1-2 mm in size," Quan says. "At Raine, the currents transport these to a distance of up to two kilometres and they build up in volume to form the island.
However, a rise in sea level, which is one of the effects of climate change interferes with the formation of these reef islands. Also, as climate change progresses and the oceans become more acidic due to their uptake of anthropogenic CO2, the forams become vulnerable.
The increased acidity reduces the ability of forams to secrete a calcium carbonate skeleton and thus, will potentially lead to a significant reduction in numbers living on the reef."
A reduction in numbers means a reduction in sediment available for island growth.
Quan and John are looking at whether it takes decades or centuries for the forams to be transported across the reef and deposited on the island, based upon variables like the ocean current and the prevailing winds. A rise in the incidence of storm activity may also hamper sediment transport.
John brought several core samples to ANSTO during a visit from 27 September to 1 October 2010. The work was carried out between several ANSTO facilities, including the ANTARES accelerator and the STAR accelerator.
Quan continues: "The terminal voltage here at ANTARES can go up to 10 million volts. However, for measuring carbon-14 (C-14), we use the terminal voltage of 5.2 million volts. John's samples, most of which are single forams with a mass range of 500 micrograms to one milligram of material or ~50-100 micrograms of carbon, have successfully been measured. Such small-mass C-14 dating by AMS is one of the capabilities available here at ANSTO."
The scientists stress that you have to have real data in order to test your model, explaining that core samples taken from the island date back to between 3000 to 4000 years in age.
"You can see how fast the accumulation rate of carbonate sand is over time, including coral sediment and foram in the various core samples. In this fashion we can see which parts of the island build more in contrast to other parts of the island; essentially, how this island formed during the past 4000 years."
Quan says climate change, sea level changes and a change in ocean temperature will be shown to have influences on the growth rates of the island through changes in sediment production and transport.
AINSE PGRA Scholarship
In 2009 John submitted an application for a Post Graduation Research Award (PGRA) Scholarship through Australian Institute of Nuclear Science and Engineering (AINSE) Ltd, because he knew that he needed to come to ANSTO to do what he needed to do.
John continues: "So AINSE provides me with not only a stipend but also travel and accommodation and research facility costs, which allows me to do my work. I was also the recipient of the 2009 John Ferris Memorial Award, which basically goes to the top applicant in the environmental science division."
When John heads back to Raine it will be during the nesting season of the Green Sea Turtles. But it won't be a case of frolicking with these languid paddlers in the temperate waters because there will be another gathering of marine life: rather large tiger sharks!
It's quite an interesting time.
"When they're in the water, we're not," he said.
Published: 01/11/2010