365 Days of Climate Awareness 61 - Antarctica

Antarctica is the frozen continent spanning the South Pole, where 80% of earth's fresh water is contained in the ice sheets covering it and ice shelves surrounding it, enough to raise global sea level by more than 60 m if it were all to melt. Antarctica is also the world's driest continent, with average precipitation lower than 200 mm (8 in) on the coast, and less than 1 inch inland. During the coldest three months of the year its average temperature is -63°C (-81°F).

Map of Antarctica.

The continent is divided by the Transantarctic Mountains into unequal halves, the larger east and smaller west. By satellite gravimetry, the underlying topography has been mapped and shows the eastern half to be largely above sea level, while the western portion is an archipelago covered with glaciers thick enough to remain grounded. It was not always frozen. In the Paleozoic Era, from 540-260 mya, east Antarctica was tropical. As the planet cooled and the continent moved south after the breakup of Gondwana after 160 mya, coniferous forests ceded to frozen ground and then ice, as it came to its present position at the pole.

The continent is 98% covered by ice, with many subglacial lakes underneath. Sea ice tends to expand in winter and shrink in summer, with satellites showing a recent shrinking trend, but not nearly as severe as in the arctic, almost certainly due to the presence of the continent itself preventing deep circulation of warmer water: in fact, the Weddell Sea is where Antarctic Bottom Water, the coldest, densest ocean water on earth, is formed.

Gravimetric map of Antarctic bedrock beneath the ice sheet. At least some of the western region would emerge above sea level once the weight of the overlying ice is removed, even with sea level rise.

Antarctica is home to surprising biodiversity. The best-known include blue and emperor penguins, several species of seals, giant squid, blue whales and many types of flying birds. Phytoplankton are the basis of the oceanic food web, but their predators, krill, are the primary prey of the whales and many fish. A wide range of fungi and microorganisms live there, though plants, dependent on water, cannot survive.

The ice shelves ringing the continent would not add much to sea level were they to melt, but they generally serve to stabilize the ice streams of the continental ice cap, which flows more quickly in areas where the shelf is removed. Recent ice mass loss from Antarctica was estimated by satellite to be 43 GT (gigatons)/year between 1992 and 2002, increasing to 220 GT/year in 2012-17, largely from the ice shelves. The eastern uplands have gained ice mass, and it is theorized that warming global temperatures will accelerate this, as warmer air will provide more precipitation, in the form of snow, to supply growth of the ice cap.

Tomorrow: Greenland.

Be well!