Ocean Acidification – an at home experiment

I wrote this piece (and spend a fraught afternoon of frenzied experimentation) for a Brighton Museum project to exploring local marine wildlife! Ocean acidification is a serious issue but this is a fun, educational and accessible way to learn more about it!

71% of our earth’s surface is covered in water. Our oceans are home to as much as 80% of all life on earth. More than 3.5 billion people rely on the oceans for food. Coastal and marine systems support more than 28 million jobs! As part of the water cycle our vast oceans also regulate our weather systems, but they also regulate the amount of carbon in the atmosphere. You might have heard forests referred to as ‘the lungs of the earth’ (and they are very important) but the oceans actually store 16 times more carbon than terrestrial ecosystems, around 30% of carbon dioxide in the atmosphere! 

If too much carbon dioxide is stored in the ocean we see something called ocean acidification. Ocean acidification reduces the amount of carbonate in the sea, affecting organisms whose bodies are made of calcium carbonate (like animals with shells and hard exoskeletons). This includes molluscs (sea snails, mussels, octopus), echinoderms (star fish and sea urchins) crustaceans (crabs, lobsters, plankton and krill) and corals. If there isn’t enough carbonate these organisms won’t be able to form properly, which could be really bad news. This is already happening to the Dungeness crab in the Pacific Ocean. Not only are all these animals important in their own right, they are vital in maintaining a healthy ocean ecosystem. Corals create homes for 1 million marine species, and the other organisms (especially krill, plankton and molluscs) make up the base of the marine food web, supporting all life above them, up to the enormous whales that depend solely on krill for their survival. 

A Brighton local the European Green Crab (Carcinus maenas) one type of animal that will be affected by ocean acidification

Let’s break down the chemistry of ocean acidification. pH is measured on a spectrum. The lower values (0-6) are acidic, 7 is neutral, and high values (8-12) are alkaline. Seawater currently has a pH of 8.1 making it slightly alkaline. As more carbon is stored in the sea, the pH drops, shifting it towards acidity. When carbon dioxide enters the water, it bonds with water to create carbonic acid. This carbonic acid bonds with carbonate in the water creating bicarbonate. This is what makes the water more acidic and is how levels of naturally-occurring carbonate begin to fall, which is where the problems start. 

Now we know all about pH and ocean acidification, let me show you an easy, and very cool, experiment that lets you test the pH of seawater (or any liquid) at home! This experiment uses the natural properties of the humble red cabbage as a magic pH indicator! Red cabbage contains pigments called anthocyanins. Anthocyanins are a group of pigments that change colour based on the pH of their environment, so using the juice of red cabbage we can transform the colour of any liquid based on its pH! Let’s get stuck in!

The Experiment!

You can also download the instructions below. Happy Experimenting!



Want to learn more? Check out these resources!




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