A planetary experiment: Ocean acidification and biology

Ocean acidification is a relatively newly recognized threat to marine ecosystems. Even coral reef scientists, many of whom are now feverishly investigating the effects of changing seawater chemistry, ranked ocean acidification as 36th out of 40th potential threats to coral reef ecosystems in 2004 [1]. Recently, the magnitude of the shifting chemical balance in the ocean has become strikingly apparent [2].

Atmospheric carbon dioxide concentrations are predicted to exceed 500 ppmv by 2100 [3]. Today, atmospheric carbon dioxide concentration is above 380 parts per million, a value not seen in the past 740,000 years, conservatively [4]. The ocean functions as a massive carbon sink and absorbs up to a third of atmospheric carbon. As carbon dioxide dissolves into seawater, it reacts to form carbonic acid, which dissociates to form bicarbonate ions and protons. The protons react with carbonate ions, converting them to bicarbonate as well. This reduces the availability of carbonate ions in seawater, a principal component of calcium carbonate–which what many calcifying marine organisms make their shells or skeletons out of. The ocean is becoming less basic, as these reactions also lower oceanic pH. The average surface ocean pH has decreased 0.1 pH units since the preindustrial era to today [5].

The ocean stands to become more acidified. Surface ocean pH stands to drop another 0.3 -0.4 units by the end of the century (remember that pH is measured on a log scale), under the IPCC ‘business-as-usual’ scenario of 800 ppm by 2100 [2].

This is a problem. Especially if you’re a marine organism whos produce calcium carbonate in some form.

Dusty Long, The Urban Times, 16 November 2010. Full article.

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