Introduction
Antarctica is the Earth's southernmost continent in the planet earth. The earth geographical south pole is located here. It is surrounded by the southern ocean as this region is situated in the southern hemisphere entirely south of the Antarctic Circle. It is the coldest, driest, and windiest continent, and has the highest elevation of all the continents.
Large scale movement of waters in the ocean basins is referred as Oceanic Circulation. Wind drive surface circulation and cooling and sinking of waters in the Polar Regions drive deep circulation. Along the Antarctica, water is usually cooled during winter and, sinks to the deep ocean.
Climate change has not only long-since ceased to be a scientific concern but also, is no longer just one of many environmental and rigid curiosity. According to the United Nations Secretary General has (2010), it is the chief, overruling environmental issue of today, and the single greatest challenge facing environmental regulators. It is a growing calamity with economic, health and safety, food production, security, and other scope.
It is a clear signal that the oceans are responding quickly to variations in climate in the Polar Regions. We find that the falling down of dense water around Antarctica forms part of a global model of ocean currents that have a strong influence on climate. This is so evidence that these waters are varying is vital.
Influences of Antarctica on Global Ocean Circulation
Antarctica exerts a significant influence on the global ocean circulation. The seas surrounding the Antarctic continent are known to be one of the most critical areas for the production of dense, saline ocean bottom water. Cold air flowing outwards from the continent over the southern Ocean rapidly cools the surface waters, promoting down welling. This tendency is enhanced by the rejection of dense, brine-rich water as sea ice forms the cooled ocean surface. Melting at the base of ice shelves contributes further to the formation of dense bottom water. Atmospheric processes in Antarctica thus play a pivotal role in the formation of ocean bottom water which moves northward and affects the ocean circulation on a global scale.
The Antarctic atmosphere can also have an impact on the global oceans in another way. The Antarctic ice sheets contain about 30 x 106 of ice. If all this ice is to melt, global sea levels will rise to about 65 metres. The mass of the Antarctic ice is maintained by the closer balance between snowfall over the continent and the discharge of ice across the coast. Both of these processes may be affected by changes in atmospheric conditions. Precipitation over the Antarctica is sustained by the transport of moist air southwards from mid-latitudes whereas ice discharge rates may be affected by changes both in atmospheric and oceanic temperatures. Changes in the local climate of Antarctica will thus have global implications through their effect on the Antarctic ice mass budget. Consequently, this brings total effects on global sea level.
Increase in southern mid-attitude dust deposition enhances atmospheric circulation or an expanded dust source and coincides with an increase in primary productivity at the Sub-Antarctic Front. This transition come out to be connected with the growth of polynya-style mixing and a higher abundance of the sea ice tolerant diatom groups in the Antarctic Ocean. They later experience declining opal production as a consequence of a longer duration of summer sea ice and, a resultant reduction in light availability. The extensive Antarctic sea ice reduces the warming effect of the Southern Hemisphere subtropical gyres on high latitudes through northward migration of ocean fronts, including reducing the inflow and its influence on overturning circulations (Lovenduski, 2007).
The extent to which sea ice affects ocean-atmosphere relations depends on the ice level and its width distribution. The width distribution describes the nature of the surface within the pack in terms of the concentration (the part of surface area enclosed) of different ice thickness categories. While sea ice affect the ocean and the atmosphere, the distribution and kind of the ice are, in turn, affected by atmospheric and oceanic changes such as temperature, wind, ocean currents, and puff up. Therefore, the ocean, sea ice and atmosphere form a complex, interactive system (Antarctic Sea Ice Processes & Climate, 2011).
Relation to Climate Change
The principal driver of global climate is the oceanic circulation. It brings about the redistribution of large amounts of heat around the earth through global ocean currents - through local scale upwelling and down welling, and via a process called thermo- halide circulation (Hays, 2005). Marine and coastal ecosystems have adapted over time to the ocean circulation patterns as research has proven today. Global climate variations alter environmental forcing mechanisms - or factors have an impact on ocean circulation - such as storm, rain, temperature, and salinity behaviours. These variations in forcing mechanisms can lead to an alteration in ocean circulation, in addition to an increase in storm movement (Center for Sea Solutions, n.d.).
Thermo- halide circulation behaves like a conveyor belt. There is cold, dense water originating from the Atlantic Ocean that sinks to the deep ocean. These waters move across the ocean basins towards the tropics where they warm and up well on the surface. The warmer and less dense, tropical waters are then drained to polar latitudes to substitute the cold falling water. Here, heat is radiated to the atmosphere, making the water to be chilly and dense thus refurnishing the conveyor cycle. Melting of polar, cold ice usually lessens the salinity and therefore, the density of polar waters, which might decline the pace at which this water goes down. Such melting would then change the movement of heat encircling the globe.
Atmospheric pressure systems generate strong winds in the eastern Pacific. These north westerly winds lead to upwelling along the western coast of North America (Rogelj, 1999). Where there is cold, nutrient-rich waters are brought to the surface; upwelling can make ocean productivity, supporting most productive fisheries globally. These wind patterns are seen changing considerably due to global climate variations (Carpenter, 2008).
Variations in global air temperatures over the ocean and the land, together with the increased temperature changes, will adjust atmospheric pressure gradients that make the strength of winds over the ocean. Stronger winds bring a rapid, powerful upwelling that provides a large incursion of nutrients in a short amount of time. This influx can add to the frequency and distribution of hypoxic events (low oxygen zones) (Bakun, 1990). Increased variability of winds owing to the varying global climate can also cause stronger and longer El Nino-Southern oscillations periods (Xu &Yeh, 2009), which are seasons whereby the waters in the Pacific tropical regions are warmer (or cooler) than standard, causing weather and climate consequences all over the globe. Such increases in undesirable ocean conditions may not be reasonable for many sea animals (Brierley & Kingsford, 2009).
Conclusion
The ocean circulation is essential for climate due to its heat transport. Abrupt climate changes can occur if the pattern of thermohaline circulation changes. It can be noted that natural variations on multidecadal time scales modulate the observed global warming signal. On the other hand, patterns of variability under global warming, as well. The thermohaline circulation plays a prominent role in supplying heat to the Polar Regions, and thus in regulating the level of sea ice in these areas, although poleward heat movement outside the tropics is significantly bigger in the atmosphere than in the ocean. Therefore, the influence of Antarctica on global ocean circulation has a substantial impact in climate change.
