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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 global effect on ocean life, there are some local cases cases where the change might be too fast for ecosystems to adapt. In particular, coral reefs are very sensitive to increases in seawater temperatures. Also, For example, when slow growing corals cannot grow quickly enough to counteract the rise in sea level, reefs can fall below the photic zone and perish (Harley, 2006).
Many biological processes are temperature dependent and could be adversely affected by even a few degrees of temperature change (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. Addition of fresh water from melting ice caps decreases surface salinities in ocean regions, which can be detrimental to species with low tolerances to changes in salinity (Harley, 2006). Significant freshwater input in high latitude regions can also stifle downwelling and stop global thermohaline circulation, radically altering global climate and current patterns.
Projected surface temperature changes by 2099. ("Climate Change 2001: The Scientific Basis," 2001)
Climate change has the potential to cause changes in water chemistry, especially with regards to oxygen solubility and the carbonate buffering cycles. Such changes may have drastic effects on certain species. As seawater warms, the solubility of most gases in it decrease. 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 (Bralower, 2002). A significant, eustatic drop in dissolved oxygen levels would detrimentally influence species worldwide. On the other hand, deep waters are generally not saturated in carbon dioxide. The ocean thus has an enormous capacity as a carbon dioxide sink. However, as atmospheric carbon dioxide levels rise, the equilibrium of the carbonate-bicarbonate-carbonic acid cycle will be shifted towards increasing water acidity (Harley, 2006). Ocean acidification would have detrimental effects on sea life, including important calcareous primary producers, such as coccolithophores.
The introduction of fresh water from melting ice caps can also affect deep-water thermo-haline currents. Because it lowers the density of water in polar region, it can prevent 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 herein regions of downwelling, thus weakening or stopping the overturn of the ocean. A current location where some models predict such an event occurring is in the north Atlantic with the shutdown of the Ocean conveyor (Gagosian, 2007). Historically this has resulted in severe cases that cause a build up Current models predict that a shutdown of downwelling in the North Atlantic could occur soon and lead to a shutdown of the ocean conveyor (Gagosian 2007). Historically, such events have resulted in build-ups of toxins in the ocean , which is that have been linked to mass-extinction events (Bralower , 2002). It is also possible that a similar event could prevent the transport of water from the tropics to the poles, causing a period of rapid climate change.A shutdown of global thermohaline circulation is also likely to cause rapid and severe changes in climate.
Warming The warming of the atmosphere is expected to result in intensified atmospheric pressure gradients. There is already some evidence that this has resulted in increasing increased storm frequency and intensity in over recent years. Atmospheric conditions are largely responsible for surface currents, which transport water in the surface layers of the ocean where most of the biomass resides (Harley , 2006). Modeling predicts that advection and upwelling will increase as a result of global warming, especially in the eastern boundary currents. Increased advection is generally linked to decreased biomass. Upwelling can often increase the biomass as it provides a source of cold, nutrient-rich water to the surface, but a strong upwelling current can also be disruptive. It is also suggested that global warming could increase thermal stratification, which would decrease upwelling (Harley, 2006).
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