The Ocean Becomes More Acidic by Human-induced CO2 Emissions

by Hannah Punitha on Nov 12 2008 5:57 PM

Researchers in Australia have discovered that the tipping point for ocean acidification caused by human-induced CO2 emissions is much closer than first thought, with estimates suggesting that the Southern Ocean could become too acidic by 2030.

According to a report by ABC News, 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 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.

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

"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," said Dr McNeil.

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.

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

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

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.

According to Mc Neil, this means that 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.