Credit: Corbis
Tilbrook, based with the CSIRO in Hobart, Tasmania, believes that though the Earth's temperature has fluctuated throughout history, the CO2 concentration of the atmosphere – and oceans – hasn't been as high as it's likely to be by 2100 at any time in the last 23 million years.
The consequences for the Great Barrier Reef in particular will be grave, he says. By way of example of what we might expect as ocean pH continues to drop, a study in the journal Science in March 2007 showed that skeletons of Scleractinian corals not only stopped growing, but completely dissolved when kept in a tank of water at a pH of 7.4 for 12 months (about the same pH as the human body).
Lough's own study, published earlier this year, points to a 21 per cent decline in the rate at which a type of Porites coral has been able to grow its calcium carbonate skeleton since 1980. The researchers – who monitored 38 colonies of the common reef builder in two parts of the Great Barrier Reef – speculate that this is evidence of ocean acidification already doing its dirty work.
But without baseline data on the carbonate chemistry of the reef waters, it's impossible to place the finger of blame, and that's what the researchers I've joined on the Southern Surveyor are planning to collect. "We need more information about the chemistry of the GBR and how this has changed, is changing and will change," says Lough, who was not a member of the research team on the ship.
"Although the potential to disrupt ecosystems is high, there is virtually no information on the carbon chemistry of the GBR region needed to evaluate the risk of acidification," agrees Tilbrook. He hopes the data they collect will be a benchmark for tracking the progression of acidification. "It's a major step in assessing how vulnerable the reef is to increasing CO2 emissions in coming decades," he says.
IN THE DAYS PRECEDING the scheduled start of the 17-day research cruise, the weather has been bad, so as I board my flight from Sydney to Cairns, I'm unsure whether I'll even be able to go out on the 66-metre science vessel. To add further suspense, the Great Barrier Reef Marine Park Authority, concerned about the disturbance to parts of the reserve that are usually off-limits, is yet to issue the necessary permits.
The next morning is the start of a clear day, however, and the park authority grants the permits. On board are Tilbrook and Matear, their team of scientists and a reporter and cameraman for the ABC's The 7.30 Report. Another researcher on board, James Cook University's Robin Beaman, is using a high-tech sonar method to map out a massive and newly discovered fossil reef that runs along the edge of the continental shelf (see "The drowned reef", Cosmos 23, p52).
During the few days aboard the ship, the researchers explain what they're doing and I watch them at work. Day and night, every couple of hours, the engine comes to a full stop and the researchers get to work in a bay that has a crane and opens onto the side of the vessel.
Decked out in lifejackets and hard hats, they dance around each other attaching cables, emptying and filling water bottles, and checking apparatus. The main purpose of this voyage is to collect thousands of samples of water from a series of depths down to the seafloor, in hundreds of different spots along the entire Great Barrier Reef.
Starting in Cairns (and then dropping me and the ABC guys off in Port Douglas) they will continue as far north as Cape Direction, before doubling back and weaving through 2,500 nautical miles all the way down to Gladstone.
In the cool night air, under the harsh glare of floodlights, they attach 24 half-metre-long grey bottles to a device called a CTD (conductivity, temperature and depth) probe. This is lowered as far as two kilometres below the surface of the ocean on a cable. The scientists then slowly winch it back up, triggering each of the open bottles to close at different depths to collect a sample of water.
Once the CTD is back on deck they cluster around it like bees to a flowering shrub, and dribble the water into hundreds of smaller bottles. These are ferried to a lab below deck, where marine chemists work through the night analysing the samples to collect data on the oxygen and CO2 content, pH and other parameters.
