Oceans face acid test

Ocean acidification is dramatically changing the chemistry of our oceans and affecting sea creatures like the humpback whale. Is it too late to turn the problem around?

At first there may just be a wisp of spray amongst the waves.

Then suddenly a humpback whale launches itself bodily from the water. With a splash that gives a hint to its size, it once more sinks beneath the waves.

In June, humpbacks migrate from their feeding grounds in the Southern Ocean to the warmer tropics to breed. All along the east and west coasts of Australia people gather on cliff tops and beaches hoping to catch a glimpse of the estimated 17,000 whales that make the journey each year.

Yet these gentle mammals are facing a threat many of the delighted spectators may not have heard of: ocean acidification.

Also known as “the other CO2 problem”, along with climate change it’s another side effect of the increasing amounts of carbon dioxide that humans are putting into the atmosphere.

Scientists say the problem is big enough that it will affect sea creatures from the tiniest microscopic crustaceans to marine giants, such as humpback whales.

Acid oceans

It’s well known that the concentration of carbon dioxide in the atmosphere is increasing because of the fossil fuels we’re burning.

It’s less well known that the ocean soaks up a lot of this carbon dioxide, buffering humans from some of the impacts of climate change. However in acting as a giant CO2 sponge, the ocean’s chemistry is affected, causing ocean acidification.

Dr Ben McNeil, a climate scientist at the University of New South Wales explains that acidity is measured on the pH scale from one to 14, with one being very acidic, seven being neutral and 14 being very basic or alkaline. Measuring the amount of free hydrogen ions in a substance gives the pH value.

“Normal pH of seawater is around 8.1. It’s weakly alkaline,” he says.

Dissolved CO2 reacts with ocean water to form carbonic acid. Until the industrial revolution this chemical reaction had not been a problem because it was — quite literally — a drop in the ocean. But then humans started burning fossil fuels more rapidly which ramped up CO2 production.

The Monaco Declaration, a statement signed by more than 150 marine scientists at the beginning of 2009, said that as much as a quarter of the carbon dioxide we produce is absorbed by the ocean.

With more carbonic acid than ever being formed, the pH of seawater has dropped slightly towards the more acidic end of the scale.

“In the last 200 years we’ve seen a 0.1 drop ,” says McNeil, who was a signatory to the Monaco Declaration.

“But pH is measured in a logarithmic scale and decreasing pH by 0.1 doubles the amount of hydrogen ions which measure acidity… It essentially means we’ve increased [surface ocean] acidity by 30 per cent.”

In June 2009, the InterAcademy Panel, a worldwide network of national science academies, stated that this “current rate of change is much more rapid than during any event over the last 65 million years”.

“If we don’t do anything [to slow carbon dioxide emissions] we’ll essentially double the acidity [of the oceans] by the end of the century,” warns McNeil.

Sara Phillips, ABC Science, 11 November 2009. Full article.

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