Ocean acidification

What is it?

Prior to the Industrial Revolution, atmospheric carbon dioxide (CO2) was 280 ppm (parts per million). Burning fossil fuels has increased atmospheric CO2 until today it’s 417 ppm and rising. In fact, we’ve produced twice as much CO2 than what the atmosphere has absorbed. Land plants and trees have absorbded around 25%, while the ocean has absorbed another 25%. And that’s changed the chemistry of the ocean.

Why is it a problem?

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Marine animals such as the plankton at the base of the food chain, such as the sea butterflies in the image and video on this page, and other creatures like shellfish and crustaceans (including krill), need biogenic calcium carbonate (CACO3) to built shells and exoskeletons. While some of the CO2 absorbed by the ocean stays as dissolved gas, most combines with water (H2O) to produce H2CO3, or carbonic acid, causing the oceans to become more acidic and reducing the availability of CACO3.

This has two key impacts : (1) less CACO3. means zooplankton can’t develop during their planktonic phase and (2) more acidic water dissolves shells and corals. There are other, unexpected impacts on marine life as well.

Colder waters hold more CO2 than warm waters, meaning the sub-Antarctic and Antarctic regions are affected faster than in warmer regions. As these areas act as nurseries for creatures at the bottom of the oceanic food web, the entire oceanic ecosystem is now threatened.

Ocean acidification is happening today faster than at any time in the last 300 million years, making it unlikely that marine organisms will be able to adapt before becoming extinct.

Sea butterflies collected in Antarctic waters 2011 showing the impact of acidification (right). Sea butterflies form the basis of the oceanic food web: from Bednarsek et al.

Why is it a problem for braided river birds?

  • Short to mid-term – reduced availability of winter food for migratory river birds that depend on hapua, estuaries, and oceans
  • Long-term – the absence of winter food for migratory river birds

Research and references