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Climate change has the potential to cause significant changes in water chemistry, especially with regards to oxygen solubility. As seawater warms, its ability to dissolve gases decreases dramatically. One of these gases is oxygen, which of course essential to most living things for respiration (Harley, 2006). Geological records from past global warming events has shown evidence of severe, large-scale hypoxic episodes (Bralower, 2002). A significant drop in dissolved oxygen levels would detrimentally influence species worldwide. Another critical area of seawater chemistry that will likely be affected by global warming is the carbonate buffering system. The ocean have an enormous capacity to take up carbon dioxide. However, as atmospheric carbon dioxide levels rise, the equilibrium of the carbonate-bicarbonate-carbonic acid cycle will be increasingly shifted toward the acidic side of the equation, lowering the pH of the water (Harley, 2006). Ocean acidification would have detrimental effects on sea life, especially important calcareous primary producers, such as coccolithophores and animals with carbonate shells. Paleoclimatic research has also shown a correlation between intense global warming events, and the build up of toxins in the ocean, which would also be harmful to fish populations (Bralower, 2002).
The introduction of fresh water from melting ice caps can also affect thermohaline circulation. Since fresh water is less dense than salt water, it floats on the surface in high latitude regions. This cap prevents the sinking of water in regions of downwelling, thus weakening or stopping the overturn of the ocean. Current models predict that a shutdown of downwelling in the North Atlantic could occur soon and lead to a shutdown of global ocean circulation (Gagosian 2007). A shutdown of global thermohaline circulation is likely to cause rapid and severe changes in climate, with similar changes in temperature to what has been recorded over the past century occurring on the scale of decades (Gagosian 2007).
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