| Summary: | The Intergovernmental Panel on Climate Change (IPCC, 2001) predicted that the atmospheric partial pressure of carbon dioxide (pCO2) will be double that of pre-industrial levels by 2100 and will be considerably higher than at any time during the past few million years. Between 2100 and 2200, the atmospheric CO2 concentration is expected to increase to the range of 1500 to 2100 ppm that is 100 times greater than the natural fluctuations seen over recent millennia, in contrast to the stability of the past 24 million years during which time levels have remained below 500 ppm (Pearson & Palmer, 2000). As CO2 dissolves in the surface ocean it reacts with water to form ‘protons’ (H+) and dissolved inorganic carbon (DIC), which is the sum of the concentrations of carbonic acid (H2CO3), bicarbonate (HCO3–), and carbonate ions (CO32–)stored in the ocean. With increasing atmospheric pCO2, DIC will increase and the equilibrium of the carbonate system will shift to higher CO2 and HCO3– levels, while CO32– concentration and pH will decrease. These changes in carbonate chemistry, often referred to as ‘ocean acidification’, are already occurring. Current models predict that the pH of surface seawater will drop from 8.0 to 7.8 by the year 2100 (Royal Society, 2005). This dramatic change in seawater chemistry is likely to have a large impact on marine life and biogeochemical processes such as reduced biogenic marine carbonate mineral production and carbonate mineral dissolution. Assessing the impact of decreasing pH on coastal ecosystems is priority and the focus here is on calcareous algae, and on coralline red algae in particular, as carbonate component of the sediment. The precipitation of calcium carbonate is a source of CO2, whereas carbonate dissolution results to lower it (Frankignoulle et al, 1994). Therefore, carbonate dissolution is expected to buffer ocean acidification and to play an important role in the global change, though it is likely that the natural process of carbonate dissolution will be too slow to ...
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