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Antarctica - Climate

Winds that flow down the surface of the ice sheet toward the coast (katabatic winds) commonly reach speeds of 80 miles per hour, and maximum measured wind speeds have exceeded 180 miles per hour. Changes in the weather are dramatic: winds shift from calm to full-gale in a brief period of time. A drop of 65F was once recorded in 12 minutes. Earths lowest surface temperature (-126.9F) was recorded at Russias Vostok Station in the interior of Antarctica. Coastal locations in summer occasionally rise above the freezing point.

Katabatic (gravity-driven) winds blow coastward from the high interior; frequent blizzards form near the foot of the plateau; cyclonic storms form over the ocean and move clockwise along the coast; volcanism on Deception Island and isolated areas of West Antarctica; other seismic activity rare and weak; large icebergs may calve from ice shelf.

The discovery of a large Antarctic ozone hole in the earth's stratosphere (the ozone layer) - first announced in 1985 - spurred the signing of the Montreal Protocol in 1987, an international agreement phasing out the use of ozone-depleting chemicals; the ozone layer prevents most harmful wavelengths of ultra-violet (UV) light from passing through the earth's atmosphere; ozone depletion has been shown to harm a variety of Antarctic marine plants and animals (plankton); in 2002, significant areas of ice shelves disintegrated in response to regional warming; in 2016, a very gradual trend toward "healing" of the ozone hole was reported.

Offshore cyclones occur with little warning. Winds typically reach hurricane strength within an hour and persist for several days. A concentration of storm formation and/or intensification occurs at approximately 50S latitude and is associated with some of the most violent seas in the world (the roaring forties). The stretch of ocean between Antarctica and the tip of South America is considered the most hostile in the world and has claimed numerous ships over the centuries.

Antarcticas ice the worlds largest area of cold (the Arctic is 35F warmer) affects and responds to world climate change. Just 20,000 years ago, the ice sheet was far larger, and correspondingly, sea level was 11 meters (36 feet) lower, as the water was locked up in Antarctic ice.

Millions of square miles of sea ice surround Antarctica; the extent annually experiences a five-fold increase and decrease, with the winter maximum more than doubling the entire Antarctic regions area of ice coverage. Icebergs larger than the State of Connecticut have been observed. The temperature gradient associated with Antarcticas sea-ice zone is one of the strongest on Earth, and the seasonal variability in the extent of sea ice is an important regulator of the climate of the Southern Hemisphere. This is primarily because of the significant difference between sea ice and water in reflecting the suns energy (albedo) and because the sea ice serves as a barrier to energy exchange between atmosphere and ocean.

The West Antarctic Ice Sheet if melted would raise sea level 5 meters. It is less stable than the East Antarctic Ice Sheet because its base is below sea level. Its low-probability/high-impact collapse has stimulated vigorous research over the last 30 years, revealing that it has largely or completely disappeared in the past after it formed but at an unknown rate. Portions of it are changing rapidly now, while averages over the whole ice sheet show little change. Some models project stability, while others suggest the possibility of rapid change.

Ice shelves extensions of continental ice sheets that are afloat on the ocean can control the rate at which their parent ice sheets or glaciers move into the sea and can respond more quickly than ice sheets to environmental change. The Larsen Ice Shelf on the east coast of the Antarctic Peninsula lost massive sections in 1995 and 2002, in response to atmospheric and oceanic warming over the last several decades. Some scientists call it a model for what could happen to larger ice shelves farther south.20 Recently observed excursions of intermediate depth water from the Antarctic Circumpolar Current have the potential to deliver tremendous thermal energy to the underside of the floating ice shelves.

The Antarctic Circumpolar Current transports 130 million cubic meters of water per second towards the east, making it the mightiest of the oceans currents. It influences formation of cold, dense, and nutrient-rich bottom water that extends throughout much of the world ocean and is a key to understanding change in the worlds ocean circulation and its influence on global climate. Recent research has shown that understanding the carbon cycle in the Southern Ocean is critically important to understanding the global carbon cycle.

Research on the marine ecosystem around Antarctica is providing an understanding of the strong coupling in the Southern Ocean between climate processes and ecosystem dynamics2 and helps to understand levels at which harvesting can take place without damaging the ecosystem. Adding to that uncertainty is the problem of ocean acidification, a gradual change in oceanic chemistry due to uptake of atmospheric carbon dioxide by the sea. The extra carbon dioxide that is produced by anthropogenic activity lowers the oceanic pH, potentially affecting the physiology of marine organism and the ability to form shells. Due to its significant role in absorbing anthropogenic carbon dioxide, the Southern Ocean is predicted to be particularly vulnerable to ocean acidification.

The annual eightfold growth and decay of sea ice around Antarctica has been termed the greatest seasonal event on Earth. It affects regional climate and the global heat budget. Particularly near the edges, it nurtures some of the worlds most productive ecosystems.

One of the best examples of basic research about Earths environment that led to important public policy decisions is the story surrounding the Antarctic ozone hole. The discovery of the annual Antarctic ozone depletion, the research that uncovered the cause of the ozone depleting reactions, and the subsequent decisions about phasing out ozone depleting CFCs is a compelling illustration of the value of science to society. Starting in 1979, ozone in the stratosphere over Antarctica has been observed almost to disappear every austral spring. In the 1990s seasonal ozone depletion in the Arctic was first observed. Elsewhere, stratospheric ozone depletions are only incremental. Stratospheric ozone keeps much of the Suns harmful ultraviolet radiation from reaching the Earths surface and therefore, the ozone hole has received widespread attention.





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Page last modified: 10-06-2017 18:28:30 ZULU