Ocean Acidification Investigation

The ocean covers about 71% of the Earth's surface and holds about 97% of our planet's total water. Despite the vastness of our oceans, they are being massively impacted by human activity. Microplastics have been found at the bottom of the Mariana Trench, fish populations are declining due to overfishing, and the oceans are warming and rising.

What causes ocean acidification?

Burning coal for energy, driving cars, and other activities that use fossil fuels release carbon dioxide into the atmosphere. The oceans absorb about a quarter of the carbon dioxide released by human activity, which might sound like a good thing, but even though the oceans are vast, the huge amount of carbon dioxide they've absorbed has caused their pH to drop, a process called acidification.

Our oceans have become about 30% more acidic over the last 200 years, a change faster than anything known over the last 50 million years!

Increasing ocean acidity is expected to have huge impacts on marine life. As with any change, some organisms will survive and maybe even thrive, some struggle to adapt, and some will not survive. The effects are wide ranging, and it's not just lost biodiversity, but a potential threat to food supplies for people.

Ocean Acidification Consequences

As seawater gets more acidic, several things happen.

The absorption of carbon dioxide by the oceans reduces the availability of carbonate ions, which are needed by many animals with shells to build their shells and skeletons.
Acidic waters also attack the shells of shellfish, making them thinner and so more susceptible to diseases and more easily eaten by predators.
Coralline algae grow less well in acidic waters. These build calcium carbonate skeletons and help hold coral reefs together. Without coraline algae, coral reefs would fall apart.
Acidic waters also slow the growth of coral skeletons and corrode existing structures.

You can use an egg and vinegar to demonstrate visually how sea creatures can lose their protective shells in increasingly acidic waters.

Ocean Acidification Demonstration

One simple way to demonstrate the effect of ocean acidification on the shells of marine life is to place an egg in vinegar and watch as the vinegar dissolves the shell.

Eggshells are made from calcium carbonate ( CaCO₃ ), which is the same substance corals, clams, oysters, and other marine animals use to build their skeletons and shells.

Acidic ocean water contains carbonic acid, but we're going to use another weak acid, which you probably have in your kitchen, acetic acid ( vinegar ).

When you place an egg in vinegar, the acid breaks down the calcium carbonate, releasing carbon dioxide gas ( you'll see little bubbles being released around the shell ). The same corrosion happens to the shells of marine organisms, but much more slowly. Vinegar has a pH of around 3, and the ocean around 8.1. The acidic ocean weakens shells over time, making them thinner and more fragile.

You might be thinking that if the ocean has a pH of 8.1, it's not acidic, but even though pH 7 is neutral and anything above that is basic, the ocean is more acidic than it was in previous years. Acidification doesn't mean the ocean is turning into acid, but rather that it is becoming more acidic, and even a very small change in pH can substantially affect marine life.