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Insights into our latest mission to the Arctic.

Ocean Acidification

April 12, 2011

Posted by: Helen Findlay (Ice Base Scientist)

If you want to understand how ocean acidification might impact some marine creatures you need to do two things. First go to the seaside and find a seashell. Then go to a shop and buy a fizzy drink, any brand will do. Put the seashell in the fizzy drink and leave it for a few days. Then have a look and see how much is still there. You will see that it is starting to dissolve away.

Helen maintains her ice sampling hole

Helen clears the sampling hole

A similar process is happening in the oceans today. Carbon dioxide in the atmosphere is being taken into the ocean. When carbon dioxide dissolves in water it forms carbonic acid. Fizzy drinks are carbonated – they have carbon dioxide bubbled into them and this makes them acidic. Carbon dioxide is taken up into cold waters more rapidly and so the process of ocean acidification affects the coldest seas, such as the Arctic Ocean, the most.

The carbonic acid in the oceans doesn’t stay as carbonic acid for very long. It quickly breaks down into bicarbonate (HCO3- ) and a hydrogen ion (H+). Acidity is the measure of hydrogen ions in a liquid. So as the number of hydrogen ions increases we say it is becoming more acidic. pH is the measure of this acidity. On the pH scale the oceans are actually basic – the current average pH level of the oceans is about 8.2 (compared to freshwater which is pH 7). By continually adding more carbon dioxide, and increasing the amount of hydrogen ions, the ocean is becoming more acidic – the pH level is dropping. The pH level will continue to decrease into the future as long as carbon dioxide keeps being taken up by the oceans.

Ocean pH is regulated by a process called ‘buffering’. Hydrogen ions reacts with calcium carbonate (both limestone and chalk are types of calcium carbonate). Continued buffering relies on there being enough chalk in the water to cope with the increased levels of carbon dioxide being dissolved into the seas, but this is a slow process and happens over thousands of years. So the rate of buffering at the moment does not match the rate of carbon dioxide addition and so the ocean buffering system is not able to prevent the rapid decrease in pH that we are seeing in the oceans today.  Since the beginning of the Industrial Revolution, there has been already been a 0.1 drop in pH level. Models predict that the pH level will continue to lower (become more acid) to 7.8 in the next 100 years and to 7.4 in 300 years.

Helen writes up her notes in a workbookThis may seem like a small amount but the impact can be quite large. For example, your and my blood pH is kept constant by processes in our bodies. If this pH level changed by 0.1 in either direction, it would be time to call an ambulance and take you straight to hospital. All organisms need to regulate their internal pH and marine creatures are no exception. The difference is that many marine organisms are more dependent on the ocean to act as a pH regulator. It is also important for those organisms that have shells made of calcium carbonate – they find it difficult to maintain their shells, which start to dissolve as the pH decreases (just like in a fizzy drink, only much slower).

The Arctic acts as a bellwether for acid levels in our seas and their impact on the marine ecosystem. Acidification is thought to happen here faster than anywhere else but there is still a lot we don’t understand about how the sea ice and associated  processes affect how carbon dioxide is taken up into the Arctic Ocean. For example, scientists had assumed that the sea ice acted like a lid, which would stop carbon dioxide from going into the ocean in winter, altering the acidification process. But new information is telling us that it is not that simple.The research being carried out here at the Catlin Arctic Survey Ice Base is trying to find out more about the transfer of carbon dioxide through sea ice, what this means in terms of ocean acidification and how acidification, or changes in these processes, might affect the organisms that live in and under the sea ice.

Dr Ceri Lewis is examining the impact of acidification on copepods. Dr Oliver Wurl is looking at processes involving algae (microscopic marine plants) and the ‘marine glue’ they excrete. I’m investigating the biological and physical processes that transfer atmospheric carbon dioxide to the ocean through the sea ice.

Posted in Blog, Ice Base, Science



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