Scientists set off on a voyage to Antarctica on March 22 to see if the icesheets at the edge of the vast continent are melting faster and whether the Southern Ocean is soaking up less climate-warming carbon dioxide.
The Southern Ocean absorbs a large amount of the CO2 emitted by industry, power stations and transport, acting as a brake on climate change.
"Some recent results suggest the Southern Ocean is becoming less effective at absorbing CO2 than it used to be," said Steve Rintoul of Australia's government-backed research arm the CSIRO. "If it were to become less effective in absorbing it, that would tend to accelerate the rate of climate change," he said.
"Our measurements of how much carbon dioxide is accumulating in the ocean will provide a critical test of this hypothesis." Rintoul is leading an international team of researchers aboard the Aurora Australis that left the southern Australian city Hobart, in Tasmania, on March 22.
The scientists from Australia, Britain, France and the United States, will spend nearly a month taking measurements of the Southern Ocean between Antarctica and Hobart to see how the ocean is changing and what those changes might mean for the world's climate.
The Southern Ocean is also a key part of the global system of ocean currents that shift heat around the planet, a key driver of the world's weather. Past voyages led by Rintoul have detected changes in the ocean that could mean ice is melting faster in Antarctica.
The latest voyages aims to test that theory and the scientists will take a variety of measurements, including salinity, temperature and ocean chemistry, such as carbon dioxide and CFC concentrations.
JOURNEY TO THE DEPTHS:
The vessel will deploy a device called CTD (conductivity, temperature and depth), that will be lowered to the sea floor about 4.5 km (3 miles) below and then takes a series of water samples as it returns to the surface. One of the most important tests will be checking the salinity of the water at the bottom of the sea. So-called Antarctic bottom water helps power the great ocean conveyor belt.
This is a system of currents spanning the Southern, Pacific, Indian and Atlantic Oceans that shifts heat around the globe. Rintoul, of Australia's Antarctic Cooperative Research Centre, says past measurements by his expeditions have shown bottom water is becoming fresher.
"If it turns out that bottom water is freshening because the ice in Antarctica is melting more rapidly, then that has implications for sea level rise and for the future behaviour of the Antarctic icesheet," he said. Normally, water at the surface near Antarctica is made so cold and salty it becomes dense enough to sink to the bottom of the ocean where.
The same thing happens in the far north Atlantic Ocean near Greenland and together this helps drive the ocean conveyor belt. This system brings warm water into the far north Atlantic, making Europe warmer than it would otherwise be, and also drives the large flow of upper ocean water from the tropical Pacific to the Indian Ocean through the Indonesia Archipelago.
If these currents were to slow or stop, the world's climate would be thrown into a chaos. "If we see the dense water formed in the south near Antarctica is changing, it might provide an early indication that this system of ocean currents, which is maintaining our climate in its present state, might be susceptible to change," Rintoul said.
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