When you make changes in a self-regulating system, everything else changes. Dr Anjani Ganase wonders about how we are intensifying the acidic ocean.
Chemistry behind ocean acidification
Our ocean absorbs about 40 per cent of carbon dioxide pumped into the atmosphere. When carbon dioxide dissolves into the ocean it reacts with the water releasing hydrogen ions to form carbonic acid making the ocean acidic. Having more carbon dioxide in the water means that the ocean becomes more acidic as carbon emissions increase. Ocean acidification limits the availability of carbonate ions for the formation of calcium carbonate shells and skeletons (think of clams, crabs, conchs, lobster).
The ocean, the largest body of water on the planet, has absorbed over 525 billion tonnes of carbon dioxide since the industrial revolution. Under more acidic conditions, carbonates are more likely to bind with hydrogen ions than calcium. Which means that formation of calcium carbonate skeletons become much more difficult. This has resulted in a decline in average pH (pH is actually measured as concentrations of hydrogen ions) from 8.2 to 8.1 of the ocean. This drop means that there has been a 30 per cent increase in hydrogen concentration (in the form of carbonic acid). We are already seeing significant ecological impacts on the marine life.
Between 2006 – 2008, oyster farmers in the Pacific north west suddenly experienced large scale die off (70 – 80 per cent) of oyster larvae. This sparked concerns over possible pollutants, but investigations revealed that the water being pumped to the farms had lower pH conditions. The waters along the Pacific northwest up well to the ocean surface from the deep. The last time this deep water might have reached the surface was between 30 – 50 years ago and would therefore reflect the acidic ocean or carbon dioxide chemistry. This is startling considering how much more carbon dioxide has been absorbed between then and now. Today, oyster farmers have to buffer their water supply with antacids to regulate the pH conditions.
Ocean acidification and coral reefs
Many ocean organisms derive their skeletons and shells from calcium carbonate. Coral reefs provide habitat to over 25 per cent of marine life in the ocean making it the most biodiverse ecosystem in the ocean, however, the foundation of this habitat is calcium carbonate. While some coral species fare better than others in adapting to the changing ocean chemistry, some species are quite sensitive owing to the formation of their skeleton and their morphology. Ocean acidification can limit coral growth, weaken the skeleton integrity and in some cases erode the fine structures.
To gain some insight into what the future of coral reefs might look like, scientists explored coral reefs growing in natural volcanic seeps in Papua New Guinea where carbon dioxide bubbles through the water. What scientists saw was a transition from the finely branching species of corals common to the area to
