| Ocean Acidification |
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CARBON CYCLE In the natural Carbon Cycle , the atmospheric concentration of carbon dioxide (CO2) represents a Balance of fluxes between the oceans, Terrestrial Biosphere and the atmosphere. Land-use changes, the Combustion of Fossil Fuel s, and the production of Cement have led to a flux of CO2 to the atmosphere. Some of this has remained in the atmosphere, some is believed to have been taken up by terrestrial Plant s, and some has been absorbed by the oceans. When CO2 dissolves, it reacts with water to form a balance of (H2CO3), Bicarbonate (HCO3-) and Carbonate (CO32-). The ratio of these species depends on factors such as Seawater Temperature and Alkalinity (see the article on the ocean's Solubility Pump for more detail). ACIDIFICATION Dissolving CO2 also increases the Hydrogen ion (H+) concentration in the ocean, and thus reduces ocean pH. Since the Industrial Revolution began, ocean pH has dropped by approximately 0.1 units, and it is estimated that it will drop by a further 0.3 - 0.4 units by 2100 as the ocean absorbs more anthropogenic CO2 (Orr ''et al.'', 2005). Although this oceanic absorption will help ameliorate the Climatic effects of anthropogenic emissions of CO2, it is believed that it will have negative consequences for oceanic Calcifying Organism s. These use the Calcite or Aragonite Polymorph s of calcium carbonate to construct Cell coverings or Skeleton s. Calcifiers span the Food Chain from Autotroph s to Heterotroph s and include organisms such as Coccolithophore s, Coral s, Foraminifera and Pteropod s. Under normal conditions, calcite and aragonite are stable in surface waters since the carbonate ion is at Supersaturating concentrations. However, as ocean pH falls, as does the concentration of this ion, and when carbonate becomes under-saturated, structures made of calcium carbonate are vulnerable to dissolution. Research has already found that corals (Gattuso ''et al.'', 1998), coccolithophore algae (Riebesell ''et al.'', 2000) and pteropods (Orr ''et al.'', 2005) experience reduced calcification or enhanced dissolution when exposed to elevated CO2. The Royal Society Of London published a comprehensive overview of ocean acidification, and its potential consequences, in June 2005 (Raven, ''et al.'', 2005). While the full Ecological consequences of these changes in calcification are still uncertain, it appears likely that calcifying species will be adversely affected. Present evidence suggests that dramatic changes in the marine environment over the next 100-200 years are inevitable. REFERENCES
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