Ocean acidification and life on the sea floor

Ocean acidification (OA) sounds like the stuff of nightmares but it’s happening now – since the start of the Industrial Revolution, the hydrogen ion concentration of the surface ocean – the variable that determines how acidic it is – is estimated to have increased by nearly 30 per cent. How? The chemistry is straightforward. As human activities produce more CO2, more of the gas enters the ocean and reacts with sea water. This releases negatively-charged (acidic) hydrogen ions and reduces pH. It’s that simple.

What isn’t simple is demonstrating the consequences; just how OA may affect marine organisms and ecosystems, including not only seaweed, sea urchins and fish, but also bacteria and plankton. There is growing evidence that some organisms, such as coral reefs, are being affected in some parts of the world, but what of the life around our own shores?

What we do know is that if we keep emitting CO2 at today’s rates, by 2100 average surface ocean pH will have fallen from 8.1 to around 7.8 – average levels the Earth has probably not experiencedfor more than 20 million years. This would have wide implications for ocean life, especially, but not exclusively, for organisms that need calcium carbonate to build shells or skeletons. Not only do increased hydrogen ion concentrations inhibit calcium carbonate formation, but they can slowly dissolve calcium carbonate structures, even if pH is greater than the ‘neutral’ value of 7.0.

Natural Environment Research Council, Full article.

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