Environment

Robots plumb changes in Southern Ocean

Sarah Wild

Off the coast of South Africa, ocean robots are sending back information to help us to understand how the ­climate is changing.

Ocean robots are sending back information to help us to understand how the ­climate is changing. (Madelene Cronje_M&G)

Off the coast of South Africa, heading towards Antarctica, ocean robots are sending back information to help us to understand how the ­climate is changing.

The recent report by the United Nations' Intergovernmental Panel on Climate Change (IPCC) paints a bleak picture, in which the days are getting hotter and the ocean is becoming more acidic. But the Southern Ocean, where you are most likely to see the change, is one of the most understudied, says Pedro Monteiro, the head of the Southern Oceans Carbon-Climate Observatory in Cape Town.

The world has always had a natural carbon cycle, with about 100 gigatonnes of carbon dioxide being exchanged between the atmosphere, the oceans and the land. Anthropogenic carbon dioxide emissions, those emitted by human activity, are magnitudes less than the total cycle at about nine to 10 gigatonnes but, "of that, half stays in the atmosphere … and a quarter goes into the oceans", says Monteiro, who is also research group leader for the ocean systems and climate research unit at the Council for Scientific and Industrial Research (CSIR).

"By adding carbon dioxide to the ocean, we're changing the ocean chemistry and that's giving life to ocean acidification," he says.

The Southern Ocean is particularly important in determining how the world's oceans are changing. It is the only ocean that is surrounded by other oceans, not land. Although it has been described as the "lungs of the oceans", there is a paucity of data about seasonal variability in the Southern Ocean and its chemistry at different depths.

"The deep ocean has 50 times more carbon dioxide than the atmosphere," Monteiro says.

That is why robot deployment, one to surf the waves and another to plumb the depths, is so important.

"For the first time, we are deploying a wave glider in the Southern Ocean but, of more significance to climate researchers, we have twinned it with a buoyancy glider that dives below the wave glider," says mission co-ordinator Sebastiaan Swart.

"This means we can link carbon-dioxide flux between the ocean and the atmosphere at the surface of the ocean [while] understanding … the connected physical and biogeochemical processes that are occurring below the surface."

Both robots, which are remotely driven from Cape Town and resemble torpedoes, are kitted with sensors that measure variables such as temperature, salinity and ocean acidity, and this data is transmitted to the observatory every hour or, in the case of the buoyancy robot, when it comes to the surface.

 

"They are like satellites but in the ocean," says Monteiro, adding that they will be picked up in February next year.

Although South Africa has the shiny new Antarctic research vessel SA Aghulas II, which has an on-board research laboratory, it costs about R250 000 a day to be out at sea, environmental affairs department officials previously told the Mail & Guardian.

"The new integrated fleet will be on a five- to six-month mission that will take both units to the Antarctic pack ice and back at a crucial period when there are currently no ship-based observations taking place," the CSIR says.

Last year, the CSIR deployed five buoyancy [deep sea] robots and Swart said at the time: "Gliders are the future. We can collect data for long periods of time without having to be there."

Students at the observatory, which is funded by the department of science and technology, are now analysing the data collected during the mission.

Monteiro, who is also affiliated to the University of Cape Town, says that the observatory has 16 postgraduate students and five supervising scientists.

"We are looking to double the size of the group in about two years."


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