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Warming of the atmosphere is expected to result in intensified atmospheric pressure gradients. There is already some evidence that this has resulted in increased storm frequency and intensity 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, biomass (Harley 2006).
Changes in conditions of water due to climate Climate change will likely change the distribution of many species. For instance as temperature rises, many species will begin shift towards higher latitudes in order to remain under similar environmental conditions (Harley, 2006). This shifting of species allows for the introduction of of alien species to ecosystems where they were not previously present, thus having the potential to greatly change the ecosystem. which can fundamentally alter 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, a location where they were rarely spotted decades ago had not been known until recent years (CNN, 2007).
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 bleaching is death can spread through the reef ecosystem. Secondary effects are most obvious in fish, which especially among those that feed specifically on corals, such as do most butterfly fishesfish. The 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. Coral bleaching is caused by high water temperatures that cause the corals to shed their symbiotic bacteria and die. More As it stands today, more than 30% of coral reefs throughout the world are already severely degraded and up to 60% of corals on 60% may be lost by 2030 due significantly to bleaching as the climate warms high-temperature induced bleaching (ARC, 2007).
It is also likely that climate change will have effects on the human aspects of many fisheries. Sea level rise may threaten many coastal areas. Thermal expansion of seawater is expected to cause a rise of 0.09 to 0.37 m over the next century (IPCC, 2001). This may threaten coastal cities, and infrastructure of the fishing industry in some areas. It is also predicted that storms such as monsoons and hurricane my increase in number and intensity as a result of global warming (IPCC, 2001). Flooding and storm surges could also result in damages to fishing infrastructure in locations prone to these disasters. Terrestrial effects of global warming could effect agriculture in certain areas by the changes in timing and intensity of droughts and flooding, as well as the effect of increased CO2 on the growth of crops and weeds. There are also likely to be effects on agriculture by sustained changes in temperature and precipitation, such as the desertification of the southwestern United States (IPCC, 2001). This could lead to a change in the demand for fish by some regions.
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The Southern Ocean (Antarctic Ocean) is important to managing climate change with respect to the worldwide ocean because the Antarctic Circumpolar Current (ACC) allows for mixing between the three great oceans. The ACC also serves to buffer Antarctica from the variable climate of higher latitudes (Gille 2002). Furthermore, Antarctic fish have a low tolerance for increases in temperature. This intolerance is due to the fact that in low temperature water, oxygen is more soluble in colder water than in warmer water, so Antarctica fish have a lower capacity for transporting oxygen in their blood, such as having fewer red blood cells. that would not be sufficient at higher temperatures (Mark 2002). Since the 1950's though the 1990's the water in the Southern Ocean has increased 0.17ºC±.06ºC. This a greater change than the overall ocean (Gille 2002).Currently fishing in the Southern Ocean is regulated by the Commission for teh Conservation of Antarctic Marine Living Resources.
North Atlantic
There is evidence of lower salinity in the North Atlantic coming from melting of polar ice caps and diluting the ocean with more fresh water. An increased amount of fresh water could come from glaciers or sea ice melting, an increased amount of precipitation or from rivers. The freshening of the oceans could have a damaging effect on the Ocean Conveyor. There are different scenarios for the slowing down of the ocean conveyor between the next two decade or in a hundred years (Gagosian, 2007). There is paleoclimatic evidence for rapid climatic changes as a result of the shut down of the ocean conveyor. If this were to happen, the Gulf Stream could possibly be deflected downwards, which would prevent the transfer of warm water from the tropics to the high Northern latitudes. In this scenario the high latitude would go through a very rapid cooling periods that could have devastating effects on the ecosystem (Gagosian, 2007). For this reason we assert that this region should be carefully monitored in order to recognize this trend early. There should also be a significant effort put into maintaining the robustness of the ecosystem in this area. To do this, restrictions placed on the fishery in this region should be higher than they would otherwise be set. If research proves this scenario is not the case, or that it will happen on longer time scales, such restrictions would be able to be scaled back.
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