Southern Ocean close to acid tipping point

By Science Online's Bianca Nogrady

Posted Tue Nov 11, 2008 10:45am AEDT
Updated Tue Nov 11, 2008 10:53am AEDT

Australian researchers have discovered that the tipping point for ocean acidification caused by human-induced CO2 emissions is much closer than first thought.

Scientists from the University of New South Wales (UNSW) and CSIRO looked at seasonal changes in pH and the concentration of an important chemical compound, carbonate, in the Southern Ocean.

The results, published in today's Proceedings of the National Academy of Science, show that these seasonal changes will actually amplify the effects of human carbon dioxide emissions on ocean acidity, speeding up the process of ocean acidification by 30 years.

Dr Ben McNeil, senior research fellow at the UNSW's Climate Change Research Centre, says the ocean is an enormous sink for CO2, but unfortunately this comes at a cost.

"The ocean is a fantastic sponge for CO2, but as it dissolves in the ocean it reduces the pH of the ocean, so the ocean becomes more acidic," Dr McNeil said.

This acidification makes life especially hard for marine creatures such as pteropods - an important type of plankton found in the Southern Ocean - whose shells are made up largely of calcium carbonate.

Tipping point

Once the acidity of the Southern Ocean reaches a certain level, the shells of these and other calcareous marine creatures will start to dissolve.

"That's a really bad point to get to," Dr McNeil said.

"After that point, we can't go back unless we suck the CO2 out of the atmosphere."

This so-called 'tipping point' of acidification had been predicted to occur when atmospheric CO2 levels hit 550 parts per million, around the year 2060.

However, the new research shows levels of the carbonate that these creatures need to build and maintain their shells drops naturally in winter, due to natural variations in factors such as ocean temperature, currents and mixing, and pH.

Dr McNeil says this means the tipping point is likely to be reached at far lower atmospheric CO2 levels - around 450 ppm, which also happens to be the target set by the IPCC for stabilisation of CO2 emissions.

"That's the benchmark that a lot of climate scientists have said we want to reach," he said, but this concentration is forecast to be reached around 2030.

Dr McNeil says ocean acidification could lead to large-scale ecosystem changes, affecting not just plankton but other marine life including fish, whales and dolphins.

"They're at the base of the food chain ... so right now we don't really know the ramifications."

http://www.abc.net.au:80/worldtoday/content/2008/s2416423.htm

Tighter timeline for ocean organisms
The World Today - Tuesday, 11 November , 2008  12:46:00 Reporter: Jane Cowan ELEANOR HALL: Now to that alarming research on marine life in the southern ocean which shows that the tipping point where animals will struggle to survive will come sooner than scientists previously thought. Researchers at the Climate Change Research Centre at the University of New South Wales are warning that acidity in the Southern Ocean will reach destructive levels where it will dissolve the shells of marine organisms by 2030. As Jane Cowan reports that is at least twenty years earlier than scientists had previously predicted. JANE COWAN: When you're a marine organism with a shell made out of calcium carbonate, one thing you don't want is an acidic ocean. BEN MCNEIL: I guess dangerous is not really, it's a sort of subjective word really. But I guess dissolving shells is definitely a consequence which would be quite problematic for a number of these organisms. JANE COWAN: That's Senior Research Fellow Dr Ben McNeil from the Climate Change Research Centre at the University of New South Wales. He's the one who made the unsettling discovery. The problem is carbon dioxide in the atmosphere. As humans pump billions of tonnes of it into the air, oceans absorb it and become more acidic. Previous estimates predicted the shells of microscopic zooplankton for instance would start to dissolve when carbon dioxide concentrations in the atmosphere reached 550 parts per million, something that was anticipated to happen around the middle of the century. But Dr Ben McNeil has found that point will be reached when carbon dioxide in the atmosphere hits 450 parts per million; something that could happen as soon as 2030. BEN MCNEIL: And the reason is that during winter in autumn in the Southern Ocean there are some circumstances which lower the PH levels quite significantly naturally and so we didn't realise there was such a large natural variation just throughout the year. When you take that into account, coupled with what we're putting up into the atmosphere that brings forth these problematic conditions a lot earlier. JANE COWAN: Dr McNeil says if acidification can't be sufficiently slowed, the organisms will just have to adapt and fast. BEN MCNEIL: I guess they're out on their own really, I'm not sure what we can do in terms of particular organisms in the Southern Ocean if we get to 450. They'll have to, hopefully they can adapt to those changes and maybe migrate north where there isn't the problems that are associated in the Southern Ocean. JANE COWAN: But migration and adaptation aren't options for some of the deep sea coral ecosystems most at risk. Ecosystems like those discovered by Dr Martin Riddle from the Australian Antarctic Division on a voyage last year. MARTIN RIDDLE: We discovered a very biologically diverse cold water, cold community ion the edge of the continental shelf of the coast of Antarctica. They can't go any shallower, they can't just migrate up the slope because they're old, slow growing animals that are highly susceptible to disturbance from ice bergs to they can't live any shallower, but if that environment changes, we may well loose them. JANE COWAN: The scientists agree these findings emphasise the need to keep carbon dioxide levels in the atmosphere below 450 parts per million. Researcher Dr Ben McNeil says reducing emissions across the globe by 60 per cent by 2050 would keep carbon dioxide concentrations within those levels. But he says the inability of developing countries to make such heavy cuts means developed nations like Australia need to increase their targets to 80 per cent by 2050 to achieve 60 per cent overall. BEN MCNEIL: I think the developed world will be starting to or need to take stronger action quicker to get to where we need to be and I know that the new Obama Administration has 80 per cent by 2050 target. JANE COWAN: That's something oceanographer Dr Will Howard from the Antarctic Climate and Ecosystems Cooperative Research Centre in Hobart would like to see. WILL HOWARD: If you really wanted to protect the ocean from ocean acidification let us say in winter when these impacts would be felt, then you would have to in theory set much sharper lower targets. ELEANOR HALL: That's oceanographer Dr Will Howard, ending Jane Cowan's report.