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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 anoxia 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 into the oceans 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).
Warming of the atmosphere is expected to result in intensified atmospheric pressure gradients. There is already some evidence that this effect has resulted in increased storm the frequency and intensity of storms 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, the lateral movement of water, will increase as a result of global warming, especially in the oceans' eastern boundary currents. Increased advection is generally linked to decreased biomass biomass (Harley 2006).
Climate change will likely change the geographical distribution of many species. For instance as temperature rises, many species will begin have to shift towards higher tohigher latitudes in order to remain under similar environmental conditions (Harley, 2006). This shifting of species allows the introduction of These species shifts can introduce alien species to ecosystems where they were had not been previously present, which can fundamentally alter these ecosystems. For instance, huge swarms of mauve stingers (Pelagia nocticula), which can devastate populations of fish, are becoming common in the waters off of Britain, where they had not been known until recent years (CNN, 2007). For some species, such as the Antarctic Icefish, there may be no higher latitudes to which they can move. For these species, climate change may well lead to extinction (Pauly 2007).
Many biological processes Many biological processes are temperature dependent and could would be adversely affected by even a few degrees of temperature change (Harley, 2006). Higher temperature waters, such as those in the tropics tend to have less primary production in the form of phytoplankton, which almost all fish derive their energy from. This results largely due to . This results from the fact that a a higher strong temperature gradient prevents the upwelling of cool, nutrient rich waters, such as is common off the coasts of Peru and Chile during the warm negative periods of the ENSO cycle off Peru and Chile (Harley, 2006). A drop in the amount of primary production causes a drop drops in the higher trophic levels as well. Therefore, in many cases, it is reasonable to predict in many cases this believe that global warming will cause the populations of fish stocks to decrease 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).
Another adverse effect from global warming is coral bleaching. When corals are stressed by high water temperatures or other effects, they expel their symbiotic zooxanthelle from their tissues. This process deprives corals of the color, as well of their primary source of nutrition. If corals are without their symbionts for too long they can perish from starvation. The impact of coral death can spread through the reef ecosystem. Secondary effects are most obvious in fish, especially among those that feed specifically on corals, such as butterfly fish. These fish were gradually starving to death and the decline in numbers indicated they had also failed to breed in the months and years following the destruction of their reef. As it stands today, more than 30% of coral reefs throughout the world are already severely degraded and up to 60% of corals may be lost by 2030 due to temperature induced bleaching (ARC, 2007). Coral reefs are also threatened by sea level rise. 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).
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