Ocean acidification: how will marine life cope?

CO2 emissions are making the oceans more acidic. We’re still not sure what this will do to marine life, but in many places the result’s unlikely to be good. Jason Hall-Spencer describes his efforts to understand the impact by investigating places where the gas bubbles naturally from the seabed.

Carbon dioxide (CO2) emissions are causing ocean acidification (OA), which certainly sounds bad. Yet the seas will not become acidic, in the sense of their pH falling below seven, even if we burn all of the wood, coal, gas and oil on Earth. So what’s the problem?

On average the pH at the surface of the oceans has fallen by only 0.1 since burning coal for steam power became widespread in the 18th century, and if we keep on rapidly burning the planet’s hydrocarbons this could fall as low as 7.4. So that’s still alkaline. The pH of coastal waters can vary widely, by a whole unit between night and day, because plants and algae take up CO2 during the day through photosynthesis, raising the water’s pH. Yet just as we breathe out more CO2 than we breathe in, marine organisms raise CO2 levels through respiration so pH levels fall again at night.

Astonishingly productive fisheries occur in upwelling regions where CO2 and nutrient-rich waters flowing up from below stimulate the growth of algae and provide abundant food. So we know marine life can thrive despite low or widely varying pH; so why have NERC, Defra and DECC just pumped £12 million of taxpayers’ money into finding out more about OA?

One reason is that the small drop in pH that we have seen since the Industrial Revolution reflects enormous changes in the concentration of hydrogen ions which are already up 30 per cent in surface waters. They are increasing so rapidly that by 2100 their concentration is expected to be 130 per cent higher than at any point in human history. (…)

Hall-Spencer J., 2015. Ocean acidification: how will marine life cope? Planet Earth, Spring 2015:20-21. Article.

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