The ocean acts like a giant sponge, absorbing a quarter of the carbon dioxide released into the air. But ocean acidification is changing the ocean\’s chemistry.
Throughout human history, the ocean has inspired countless poets with its beauty and awed early seafarers with its relentless power. A constant throughout our existence, we have always assumed that the vast seas that cover most of our planet were as immutable as the sun and stars. We were wrong.
The ocean is changing—because of us. It is now well known that we are increasing the level of carbon dioxide (CO2) in our atmosphere through deforestation and by burning fossil fuels. What you may not know is that our biosphere is trying to balance itself by drawing excess CO2 into the ocean. The ocean acts like a sponge, absorbing about a quarter of the CO2 we release into the air every year.
At first scientists were grateful for the help: the ocean has absorbed about half of all CO2 ever produced by humans and has slowed down climate change. But the ocean can no longer hold back the rising tide of carbon. Newer research has shown that we are altering the chemistry of our seas in a process known as ocean acidification.
What is ocean acidification?
When carbon dioxide enters seawater, it is converted into carbonic acid, the same acid that puts the fizz in carbonated beverages. However, ocean acidification does not mean the seas will turn into a giant pool of fizz. Rather, it refers to a lowering of the ocean’s pH level. Anything under 7 is acidic; the ocean has fallen to 8.1.
Variance in the ocean’s pH—or acidity—levels is actually a natural occurrence. The slow weathering of terrestrial rock introduces ions that usually act as a counterbalance to keep carbonic acid in check. But at the current rate of CO2 emissions, nature can’t keep up.
Spurred on by human activity, increased ocean acidification has led to a 30 per cent rise in acidity since the industrial revolution. At the current rate of increase, the pH will fall 0.5 units by 2100, which is about 100 times faster than what has been shown to occur naturally. If CO2 emissions are left unabated, the coming centuries could experience changes in ocean pH greater than any experienced in the last 300 million years.
Imagining the future
To determine how this rapid sea change will affect marine life in the future, scientists are looking into the past and present for clues.
Around 56 million years ago there was a mysterious surge in carbon that is comparable to the massive CO2 influx happening today. Geologists found a layer of sediments from this era that reveal the result of rapid acidification: carbonate plankton shells dissolved, a number of single-celled organisms went extinct and animals who fed on these organisms probably disappeared as well. This level of mass extinction indicates a major catastrophic event.
Examining the present, scientists have found that the waters around volcanic vents on the ocean floor are rich with carbonic acid. Bubbles of CO2 rise from the vents and dissolve, offering a unique view of what a future carbonised ocean might look like.
The sea near Naples, Italy, is one such microcosm: many native species are absent, and the few limpets that wander into this dead zone have thin, transparent shells. A volcanic reef in Papua New Guinea reveals a similar reduction of diversity. A few organisms can adapt, but most lose out.
To test how some marine animals would fare in a more acidic ocean, scientists raised them in acidic water and observed the results. The test subjects did not fare well. Clownfish larvae could no longer locate a suitable reef habitat due to a failure in their sensory abilities.
Squid eggs, meanwhile, hatched later and were smaller. In addition, the squids could not swim straight due to an abnormal growth of their statolith, an organ that helps squids orient themselves. Needless to say, these young creatures would not last long in the ocean’s competitive ecosystem where only the strongest survive.
New research by the Australian Antarctic Division reveals that as oceans become more acidic, Antarctic krill—the main source of food for whales, seals and penguins—could be in jeopardy. “Disturbingly, our findings predict that krill will be unable to hatch or develop in vast areas of the Southern Ocean by the year 2300 if CO2 emissions continue to be released at the current rate,” warned the study’s lead author, Dr So Kawaguchi, adding that a significant decline in krill numbers would threaten the entire Antarctic ecosystem.
Impact in the present
Unfortunately, this foreboding view of the future may not be far off. There is disturbing evidence that ocean acidification is already harming marine life.
Over the past several years, oysters along the west coast of Canada and the US failed to reproduce because corrosive seawater prevented their shells from forming. After losing millions of dollars, the shellfish industry managed to mitigate the damage through various measures—some hatcheries have taken the extreme step of dosing their tanks with an antacid.
Coral reefs appear to be under assault as well. Coral forms its skeleton through calcification, a process that is slowed down by ocean acidification. In addition, the resulting reef is weaker and more easily eroded. A 2009 study showed a 14 per cent decrease in Australia’s Great Barrier Reef since 1990. Another study found a 25 per cent decrease in brain coral around Bermuda over the past 50 years.
A quarter of all fish species live in coral reefs, and about 500 million people depend on the reefs for their livelihoods, but by 2050, some experts predict that nearly all of the world’s coral reefs will be threatened with extinction.
The human cost
In Australia, the Great Barrier Reef generates over $5 billion annually in tourism and fishing revenue. The destruction of the reef as a result of global warming and ocean acidification is likely to take a huge financial toll on these key industries.
Over in the US, around 20 per cent of primary fishery revenue comes from shell-forming molluscs and crustaceans that are sensitive to ocean acidification.
In Canada, the chief concern is with the Arctic region. This area is particularly vulnerable to ocean acidification as cold water absorbs CO2 more readily than warmer water. In addition, freshwater from melting ice is less effective at neutralising carbonic acid. Just as the Antarctic krill is endangered, so too are the species that inhabit the Arctic Ocean.
Canada’s First Nation peoples would likely be the first to feel the negative effects as they rely on marine life in the region for food. Arctic fisheries may experience economic hardships as well. But decreasing shellfish populations would come to affect the rest of the global population; 16 per cent of the animal protein eaten around the world comes from fish, including shellfish.
At this point in time, the magnitude of the coming changes is uncertain. More research on the human and economic impact of ocean acidification is needed so we can prepare ourselves.
Saving our seas
One thing we do know is that we have to decide what kind of a future we want to create. The simple approach to ocean acidification is to drastically reduce our carbon dioxide emissions. For example, cities can join the C40 Cities Climate Leadership Group, which encourages cities to use alternative technologies and to reduce the carbon footprint of individuals. In Australia, both Sydney and Melbourne are members.
But the issue is a complicated one. Reducing CO2 to a level that would protect our oceans would require cutting global emissions by about 85 per cent by 2050. However, political imperatives and lifestyle choices are slow to change.
Also, ocean health is stressed by other factors, such as increasing water temperatures and lowered levels of oxygen in our oceans. The interaction between these factors and ocean acidification must be determined by increasing our research and monitoring efforts.
Communities may aim to reduce high loads of nutrients (such as nitrogen and organic carbon) in soil runoff, as this can cause ocean acidification in nearby coastal oceans. Nutrients can enter the ocean from improperly managed farms, grazing lands, dairy lagoons, urban runoff and even excessive fertilisers from residential lawns.
We can stop this land-based runoff by investing in effective sewage treatment plants, through better watershed management and through legislation. For more tips and ideas about what you can do to fight ocean acidification, check out the sidebar.
Whether we stop acidification or whether we adapt to it, we can no longer romanticise the ocean as a bastion of invulnerability. That cruel and powerful mistress of old may have haunted the dreams of early sailors, but was always a home for an astonishing variety of life. The power has now shifted to us—we can nurture the ocean so that life continues to thrive, or we can turn the ocean down a darker path, where its waters will be cruel indeed.
5 ways to help save our ocean
As individuals, we can make a difference. Here are some ideas.
- Encourage your mayor to have your community become a C40 City (c40cities.org) that is committed to reducing greenhouse gas emissions.
- Reduce your carbon footprint by consuming less energy in your daily life. For example:
- Use less electricity at home by unplugging electronic devices when not in use.
- Buy local food; imported food requires more energy to reach your table.
- Drive your car less by opting to walk, cycle or take public transport.
- Remember to reduce, reuse and recycle; consuming less is a healthy lifestyle choice.
- Keep ocean ecosystems robust by making sustainable seafood choices. You can, for instance, choose seafood and shellfish rated highly by the Sustainable Seafood Guide (sustainableseafood.org.au).
- Urge Australia’s federal leaders to move ahead with clean energy development and support Australian organisations working towards a clean energy future, including the Australian Conservation Foundation, Greenpeace and the Climate Institute.
- Educate yourself on the issues facing the ocean so that you can influence change in your local community.