MCMURDO DRY VALLEYSThe McMurdo Dry Valleys are snow free valleys in Victoria Land, west of McMurdo S

MCMURDO DRY VALLEYSThe McMurdo Dry Valleys are snow free valleys in Victoria Land, west of McMurdo Sound in Antarctica. They are considered the driest, coldest, and windiest desert on Earth. The valleys are 4,800 square kilometres and constitute around 0.03% of the continent; they form the largest ice-free region in Antarctica. The valleys were carved out by glaciers, which have retreated and left valley floors and walls with a desert pavement surface of weathered boulders gravels and pebbles. The soils underneath are up to 5 million years old with very little organic carbon and nitrogen. The region is a cold desert ecosystem. It is cold, extremely arid and windy due to the ‘rain shadow’ effect: air rolling from the polar plateau to the coast is forced over the Trans Antarctic Mountains, then cools, condenses and deposits its moisture as snow. The conditions in the Dry Valleys are also caused by katabatic winds; these occur when cold, dense air is pulled downhill by the force of gravity. The winds can reach speeds of 320 kilometres per hour, heating as they descend, and evaporating all water, ice and snow. The valleys receive the equivalent of only 10 cm average of water each year in the form of snow.The Wright Valley has an annual mean temperature of –19.8°C and its annual precipitation is less than 100 mm water equivalent; available water is usually a result of summer glacial melt.There are many alpine glaciers within the Valleys, and it seems the general trend of the glaciers is recession. Two of the large valley glaciers (Mackay and Ferrar) act as outlets to the East Antarctic Ice Sheet. The Dry Valleys are also home to Antarctica’s longest and largest river, the Onyx. The water flows of the Onyx occur only in summer, and almost all of the water is provided by glacial melt.There are many lakes and ponds found in the region, including ‘dry bottomed’ lakes like Lake Vida, which freeze completely solid in winter. Most of the larger lakes still have liquid at their base, but have an ice covering all year round. Microbial communities have been found within the water column and on the lake floors inflows. Some of the lakes have inflows of water but no outlet and a briny layer of water forms at the bottom. Some smaller water bodies are hypersaline (high salt content) so the water does not freeze at all. Robert Scott discovered the Valleys in 1903 and referred to one of them as “a valley of death.” This however is not true: the Dry Valleys are home to extremophiles, organisms that live in extreme environments. Lichen, mosses, cyanobacteria and algae have been found, as well as tiny invertebrate animals like rotifers, tardigrades and nematodes. Living bacteria have been found also, including the example of the anaerobic bacteria found under the Taylor Glacier, near Blood Falls [https://www.facebook.com/photo.php?fbid=387070261354024&set=a.352867368107647.80532.352857924775258&type=3&theater].The Dry Valleys are often described as the closest terrestrial environment on Earth to the planet Mars.-TELhttp://www.mcmurdodryvalleys.aq/http://atlasobscura.com/place/mcmurdo-dry-valleyshttp://www.amusingplanet.com/2012/06/mcmurdo-dry-valleys-of-antarctica.htmlPhoto: http://j-times.ru/wp-content/uploads/2012/06/Dry_Valley2.jpg -- source link

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