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The melting of glacial ice and the thermal expansion of ocean water will cause sea levels to rise in future years. While this is unlikely to have a great effect on most ocean life, there are some cases where the change might be too fast for certain ecosystems to adapt. This could be a particular problem with coral reefs, which might not be able to grow fast enough to counteract the rise in sea level (Harley, 2006). The loss of these ice sheets is also expected to contribute to global warming, as it would lower the albedo of the earth, causing less solar radiation to be reflected back out into space (IPCC, 2001).
In the next century, models predict average water temperatures will increase by 1 to 7 degrees celsius (IPCC, 2001). Many life processes in animals and plants are dependent on temperature, and could be significantly altered by a rise of even a few degrees in temperature (Harley, 2006). Higher temperature waters, such as those in the tropics have less primary production in the form of phytoplankton, which almost all fish derive their energy from. This is mainly due to the fact that a greater temperature gradient causes more intense stratification of the water, thus weakening the upwelling of cool, nutrient-rich water to the surface. A decrease in primary production causes a decrease in the numbers of individuals at higher trophic levels, such as carnivorous fish (Harley, 2006).
Changes in the temperature of ocean water have the potential to cause significant changes in water chemistry, especially with regards to oxygen solubility. As . Addition of fresh water from melting ice caps decreases the salinity of ocean regions, which can be detrimental to species with low tolerances to changes in salinity (Harley, 2006). Also, as seawater warms, its ability to dissolve gases decreases dramatically. One of these gases is oxygen, which is essential to all animals for respiration (Harley, 2006). Geological records from past global warming events has shown evidence of severe, large-scale hypoxic episodes, sometimes reaching global scales (Bralower, 2002). A significant drop in dissolved oxygen levels would have a detrimental effect on many species. 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 shift towards greater amounts of carbonic acid, lowering the pH of the water (Harley, 2006). Like temperature, there are many species who are sensitive to even small changes in pH. Ocean acidification would have detrimental effects on sea life, especially important calcareous primary producers, such as coccolithophores, and animals that posses carbonate shells. There is also geological data which indicates build up of toxins in the ocean during intense global warming events (Bralower, 2002).
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