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Paragraphs 1, 2 and 3
- Antarctica is a zone of net cooling. As a continent it receives less solar energy than it loses by
infra-red cooling. Even the 24 hours of daylight in the Antarctic summer cannot compensate for the generally low angle of the sun’s rays. Furthermore with 99.5% of the continent’s surface covered by snow and ice, and the extensive ice shelf, the continent has a very high albedo reflecting up to 85% of the incident solar radiation.
- Cold dense air at the surface leads to an almost permanent temperature inversion. This air
accelerates down slope to form katabatic winds which are funnelled down the steeper coastal slopes.
- In terms of the global energy budget, the net cooling of polar regions is balanced by the transfer
of heat from lower latitudes by the atmosphere and oceans. Within the general circulation of the southern hemisphere, heat is transported to Antarctica by weather systems originating in midlatitudes. Large temperature gradients between the cold continent and relatively warm sea create low pressure areas over the oceans which travel east/south-east with the prevailing north-westerlies. The tracks of the lower pressure areas create a persistent band of low pressure known as the circumpolar trough. Occasionally depressions penetrate the Antarctic Polar high to bring cloudy, wet and relatively mild weather especially to the Antarctic peninsula (see Figure 2(a)). Figure 2(a)
Paragraphs 4, 5, 6 and 7
- However, water has a greater specific heat so potentially the oceans are also extremely important
in moving heat from the tropics to the poles. In the Southern Ocean the thermohaline circulation (THC) results from an input of extremely dense cold water from the ice shelf areas such as the Weddell Sea, known as the Antarctic conveyor (see Figure 2(b)). The cold dense water sinks to the bottom of the Southern Ocean which clearly has a major impact on oceanic circulation as it is replaced by warmer surface water from the tropics. Even so, research suggests the circulation is less strong than in the Arctic where the Atlantic conveyor is of major importance climatologically.
- Counter-rotating currents of cold and sub-Antarctic water interact with the subtropical water
moving south. The resulting turbulence in the Southern Ocean between 50ºS and 60ºS is known as the Atlantic convergence. It drives nutrient rich water to the surface thus increasing primary productivity. Phytoplankton supports great swarms of crustaceans known as krill, which form the staple diet for the rest of the marine ecosystem (see Resource 5 on page 8).
Resulting changes to ice sheets
Clearly any major changes to the ice sheet would have a major impact on atmospheric and oceanic systems because of their interconnectivity.
The Antarctic atmosphere could also have an impact on the global oceans in another way. The Antarctic ice sheet contains around 30 x 10km³ of ice. If all this ice were to melt, global sea levels would rise about 65m. At present there would seem to be a close balance between inputs (snowfall) and outputs (discharge of ice from coast by calving and basal melt of ice sheets) leading to a constant mass balance of the ice store, but recently many ice sheet areas have been retreating (see Figures 2(c) and 2(d)). The ice mass is sustained by precipitation resulting from the movement of moist air southwards from mid-latitudes. Ice discharge rates may be affected by changes in atmospheric or oceanic temperatures thus changing the volume of ice store. The possible impact of global climate change resulting from enhanced greenhouse effect on Antarctica is therefore a key question for scientists to research (see Resource 3 on page 6).
- British Antarctic Survey.
Summary of the resource
- Zone of net cooling - receives less solar energy than it loses by infra-red cooling
- Very high albedo due to 99.5% coverage with snow and ice.
- Temperature inversion due to cold dense air at surface
- Accelerate down hill to cause katabatic winds
- In terms of the global energy budget, the net cooling of polar regions is balanced by the transfer of heat from lower latitudes by the atmosphere and oceans.
- Heat is transported to Antarctica by weather systems originating in mid-latitudes.
- Low pressure present over oceans due to large temperature gradients between cold land and relatively warm sea
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