The effect of acidation on polar oceans

Acidification of the earth’s oceans has been gaining increasing attention over the last five years or so, with attendant concerns about the likely consequences for marine species, ecosystems and resources important to coastal communities.

One of the main effects associated with ocean acidification is increasing difficulty for marine organisms to form calcium carbonate shells or skeletons. Not surprisingly, most attention has been focused on the tropics, with concerns articulated for our iconic Great Barrier Reef and for island communities across the Indo-Pacific region that live on carbonate sand islands protected by carbonate coral reefs that might be weakened and, ultimately, eroded as ocean acidification progresses.

Less well publicised, however, is the fact that the first significant effects of ocean acidification are likely to be seen in the cold polar oceans, especially the Southern Ocean. The acid state of the ocean is driven by a collection of chemical processes but a major driver in them is the amount of carbon dioxide that is dissolved into the ocean form the atmosphere. Anthropogenic emissions of carbon dioxide have increased atmospheric concentrations of carbon dioxide, which have, in turn, driven more carbon dioxide into solution in the oceans. The ocean uptake of carbon dioxide is greater in colder water, and so is at its maximum in the chilly circum polar waters of the Southern Ocean. Current modelling of these processes indicates that the surface layers of the Southern Ocean (the top few hundred metres) will be ‘the first cab of the acidification rank’ and become hostile to the formation of shells by marine organisms before any other part of the earth’s oceans.

Researchers at the Antarctic Climate and Ecosystems CRC have now demonstrated significant reductions in shell mass and thickness of several Southern Ocean marine plants and animals that appear consistent with the projected effects of recent acidification of the ocean. It is still early days in this research, but we now have clear empirical evidence that the concern about ocean acidification and its likely effects on marine organisms is well founded. We now need to resolve how best to unravel how such effects might spread throughout the ocean and what will be the higher ecosystem consequences of them, for both marine systems and human communities that depend on them.

Bruce Mapstone is the CEO of the Antarctic Climate and Ecosystems Cooperative Research Centre.

Bruce Mapstone,, 13 August 2008. Article.

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