Polar deserts

One-third of the Earth's surface is desert, with polar deserts covering approximately 1.93 million square miles (5 million square kilometers). Polar deserts are areas that receive less than 10 inches (250 millimeters) of precipitation per year, and have a mean temperature of less than 50 degrees F (10 degrees C) in the warmest months of the year.

Frequently, the temperature fluctuates, and it often crosses the freezing point. Polar deserts can be found around the world, including the continent of Antarctica and the Arctic, including portions of Alaska, Canada, Greenland, Iceland, Norway, Sweden, Finland, and Russia. The Antarctic is the largest desert in the world, covering approximately 5.5 million square miles (14.25 million square kilometers). Because they are among the coldest places on Earth, these areas are also among the driest. Only the heartiest of plant life can survive, and animal life is centered in coastal areas where food is abundant and available from the surrounding waters.

The Arctic is a polar desert, and is the second-largest desert in the world, encompassing approximately 5.3 million square miles (13.73 million square kilometers). The Arctic region near the North Pole is primarily ocean beneath its thick layers of ice, whereas the Antarctic region includes the South Pole and the continent of Antarctica. The Arctic Ocean is warmed by the waters of the Atlantic Ocean, thus areas of the Arctic support human, plant, and animal life. Antarctica is cut off by a cold ocean current that flows around the continent, making the region even colder. Antarctica has no native human population. The Arctic Ocean has an average winter temperature of 15 degrees F (minus 26 degrees C) and an average summer temperature of 26 degrees F (minus 3 degrees C). On top of the Antarctic ice cap, the average winter temperature falls to minus 76 degrees F (minus 60 degrees C) with an average summer temperature of minus 26 degrees F (minus 32 degrees C). Central Greenland is covered with ice that is approximately 5,000–8,000 feet (1,524–2,438 meters) thick, making for extreme cold temperatures and an extremely dry environment.

Only about 3 inches (8 centimeters) of snow falls here each year, and as a result of the extreme temperatures, it does not melt. Small amounts may be lost through sublimation, where the precipitation vaporizes before actually reaching the ground and accumulating. Even this small amount of yearly precipitation is thickening the ice by approximately 0.8 inch (2 centimeters) each year. The Greenland ice sheet of the polar desert region encompasses an area of roughly 656,000 square miles (1.7 million square kilometers).

Antarctica encompasses a larger area, approximately 4.8 million square miles (12.4 million square kilometers), equivalent to an area roughly the size of the United States and Mexico combined. Antarctica is the highest, windiest, coldest, and driest of all the continents, covered by a sheet of ice that ranges from 1 to 3 miles (1.6 to 4.8 kilometers) thick in places. The Antarctic Peninsula and coastal regions receive approximately 8 inches (20 centimeters) of precipitation each year. Most of the continental interior lands receive as little as 2 inches (5 centimeters) of precipitation each year. Like Greenland, Antarctica is dry because of the extreme cold temperatures. Coastal areas may reach 32 degrees F (0 degrees C) for a short period during the summer months, but never in the interior land. The warmest month is December, and the coldest is August. The North or South Poles never face the sun directly, and the sunlight that does reach the area is spread over a large surface area, providing little warmth.

Polar deserts are dry because of the cold temperatures. The amount of water vapor the air can hold is in direct correlation to the air temperature. Cold air simply cannot hold moisture, which results in a dry desert condition. In addition, the high altitude of the regions of polar deserts contributes to its dryness. Solar radiation and heat are reflected off, rather than being absorbed by, the ground. Cold, dense air produces permanently high atmospheric pressure, which prevents moister air from entering the regions. As air rises, it cools, turning moisture in the air to rain or snow. Sinking air has lost its moisture through the precipitation process. In the polar desert regions, dry air is continually sinking, resulting in little or no precipitation, blue skies, and a dry environment. Winds are strong and continually blow across the polar desert biome.

Polar Regions and the Midnight Sun

There is technically one day and one night each year at (or very near) the North and South Poles, with each day lasting six months. The sun cycles through the sky every 24 hours, remaining above the horizon for a six-month period. Once the sun does set below the horizon, the region is plunged into a six-month period of darkness and bitter cold. At the North Pole, the dark winter lasts from September 21 through March 21, whereas at the South Pole it will be the opposite with summer lasting from September 21 through March 21.

This strange pattern of day and night occurs because the North and South Poles are located close to Earth's axis. While the Earth spins, turning our day into night over a 24-hour period, the North and South Poles stay virtually in the same place. The six-month day and night is a result of the slight tilt in the Earth's axis, allowing for a slight movement where day turns into night. Six months of daylight seem as if they would warm the areas and melt the ice and snow, but it is not so. The sun hangs low in the sky, where the ice and snow reflect away much of the light and the sun's heat.

McMurdo Dry Valleys of Antarctica

Found in Antarctica near the Transantarctic Mountains, this rocky polar desert area has been free of ice for millions of years. The Dry Valleys receive no precipitation or moisture of any kind. Included in these ice-free valleys are the Taylor, Wright, McKelvey, Balham, Victoria, Barwick, Miers, Marshall, Garwood, and Salmon Stream Valleys. Several lakes can also be found in this region. Although frozen most of the year, these lakes are over 98 feet (30 meters) deep and contain ice that is several meters thick.

Lake Vanda, found in the central region of the Wright Valley, is approximately 3 miles (4.8 kilometers) long and up to 250 feet (76 meters) deep. This is a hypersaline lake, which allows for the water to reach a temperature of 80 degrees F (about 27 degrees C) near or at the bottom of the lake. A thermal inversion occurs as a result of the saline content, where the water is heated through the ice.

With the warmer temperature, a variety of algae, bacteria, and microorganisms live within its waters on and in the ice. Lake Vida, one of the largest lakes found in the Victoria Valley, is presumed to be frozen solid. Lake Vostox, buried under 2 miles (3.2 kilometers) of ice, is around the size of Lake Ontario, but is twice as deep. Its makeup has yet to be explored.

In the Dry Valley region, Antarctica's only river can be found. The Onyx flows only in the summer months. Lake Vanda is fed by the Onyx, which carries glacial runoff. Lake Vanda is considered a closed-basin lake because water may enter, but none will exit. Numerous shallow ponds can also be found in the McMurdo Valleys. Don Juan Pond, located in the Wright Valley, remains liquid year-round because of the hypersaline content of the water, even with surrounding temperatures reaching as low as minus 40 degrees F (minus 40 degrees C). Taylor Valley is home to Blood Falls. Iron oxide has turned the hypersaline water source blood red in some areas. Water sporadically emerges from small fissures in the ice, forming red cascades; thus, the Blood Falls name.

The rocks in the Dry Valley are home to bacteria called cyanobacteria, which can lay dormant for many years. Cyanobacteria have been found in the most barren area of Antarctica and in the high Arctic. When the rocks are damp, the cyanobacteria spring to life, producing food from the sun's energy. Cyanobacteria appear in the springtime, and with their green photosynthetic material, they turn the semi-permanent snowfields and glaciers blue-green in color. In the 1970s, the McMurdo Dry Valleys area was thought to resemble the surface of the planet Mars, with its dry desert climate and landforms. NASA utilized this Dry Valley region to test its space vehicles before launching them into space.

Polar Plant Life

Numbing cold, icy winds, darkness, and lack of shelter all contribute to the plant life of the polar desert region. When the polar desert areas surrounding the North and South Poles are dark, the plant life will either become inactive under the snow and ice or die after setting seed. These seeds will then become active the following summer, and the inactive plant life will become active as the temperature rises. Plants need sunlight, water, and soil to root. Skeletal soil composition and stony ground are common in a polar desert region. Freeze-thaw cycles result in cracking and the formation of a patterned texture to the ground. Physical weathering is the prominent erosion process. Woody plants are absent. There is not enough water in a polar desert region to sustain their growth.

In addition, the constant freezing wind without shelter stunts the growth of taller plants. Vegetation covers less than 5 percent of the ground surface, and most growth is less than 4 inches (10 centimeters) high. As a result of the severe wind and cold, plants within a polar desert have developed a vertical plant structure, growing sideways close to the ground, rather than upward. Cold desert plants are scattered throughout the region, where areas with significant sunlight will have roughly 10 percent of the ground covered with plants. All of the plants growing in a polar desert are deciduous, and may contain spiny leaves. Permafrost is permanently frozen ground found in a polar desert region, which makes it extremely difficult if not impossible for root systems of plants to take hold, thus anchorage and absorption of water and nutrients from the ground is impossible in much, if not all, of the area.

Grasses, lichens, algae, and mosses are the main component of a polar desert plant community. Algae are plantlike organisms that live by photosynthesis. They have no leaves, stems, or roots, and by definition are not true plants. On the rocks and ice of Antarctica, brilliant red, green, and yellow patches of algae can be seen. Mosses and lichens lack a significant root system, making them bryophytes, or nonvascular plants. This also makes them dependent upon their immediate environment for water because they are unable to absorb any through a nonexistent root system. Lichens are small and slow growing plants, poikilohydric in nature, capable of surviving extremely low levels of water. They thrive in places where higher plants have difficulty growing such as bare rock, sterile soil or sand, and structures such as walls, roofs, and monuments.

Like mosses, they do not have a root system, and like mosses, lichens have the ability to enter a metabolic state called cryptobiosis, where they are able to dehydrate themselves to suspend biochemical activity. In this state, lichens are able to survive extreme weather conditions in areas that are often inhabitable. Lichens are made of fungus and algae living together. They are a slightly more sophisticated life form than algae, and they are among some of the hardiest living creatures on Earth. They can grow on any surface, turning them brilliant shades of orange and gold. Lichens are capable of growing on bare rocks, and they especially like darker rocks as they warm up in the sunlight quicker than pale rocks. Lichens have survived temperatures of minus 460 degrees F (minus 273 degrees C) in a laboratory setting. They also provide the starting point for the polar desert mosses. Lichens coat rocks, causing a rough surface where the mosses can then grow.

Mosses are soft, small, nonvascular, herbaceous or nonwoody plants, which tend to grow close together in clumps or mats in damp or shady areas. They have thin, wiry stems covered by leaves, and are without flowers, fruits, cones, or seeds. Rhizoids, thin rootlike filaments, are used for anchorage and absorption. Mosses reproduce with spores. Food is produced through photosynthesis, and mosses have the ability to dehydrate and rehydrate themselves as necessary for survival, sometimes for months when enough water and sunlight become available to restart the photosynthesis process. Both mosses and lichens trap windblown dirt, creating a small layer of soil.

Antarctica's only two flowering plant species grow as a result of this process, where they can find nutrients and a foothold to survive within this small amount of soil. Antarctic hairgrass and pearlwort (colobanthus) can be found on the South Orkney Islands, the South Shetland Islands, and along the western Antarctic Peninsula, where they will grow within moss-lined crevices of rock. Here, the climate is milder than within the interior of the continent. All living things in the polar desert have adapted to their environment. The biggest challenges are staying warm, finding water, locating shelter from the extreme conditions, and producing food. Polar plants have adapted to the environment, where the stems and leaves of plants are covered with tiny furry hairs. These hairs are used to trap warmer air around them. Plant life must also contend with gale-force winds and freezing blizzards. Utilizing a vertical growth pattern, arctic plants grow closer to the ground, where the wind speed is slower and the temperatures are slightly warmer.

Polar Animal Life

The biome for a polar desert is an ocean shore environment. All the animals found here feed from the ocean. Some animals may go onto land to rest or reproduce, but their food comes from the icy ocean waters. Primary producers include tiny diatoms, crustaceans, and protozoa. These microscopic unicellular creatures find their nutrients from the bottom of the ocean.

Primary consumers include small fish and squid, which in turn eat the primary producers. The most important are krill, which are small squid-like animals found in great numbers. Second consumers include blue and humpback whales, seals, and fish that feed off the krill and smaller fish. Penguins and seabirds also feed on krill, making them a very important part of the food chain of the polar region. Top predators include polar bears and killer whales. They will consume whatever they can find, often feeding on penguins and seals. In the polar desert of Antarctica, birds live along the coastal regions, feeding from the ocean. Two penguin species nest in Antarctica: the Adelie and Emperor Penguins. Large colonies can be found roosting on the rocky coasts and islands. Snow petrels and South Pole skuras, predatory birds, hunt and threaten the penguin breeding grounds. Snow petrels and South Pole skuras fly inward and nest on the rocky outcrops and in the dry desert valleys. Ross seals live deep within the sea ice and Weddell seals live on permanently frozen ice shelves.

Adaptation to the cold temperatures is essential for life. The ptarmigan is one of the few arctic bird species that does not fly south for the winter months. They change color from brown to white as the wintery weather arrives. They have developed fluffy feathers on their feet and dig tunnels in the snow to keep warm. Seals and walruses utilize blubber, along with an extra insulating feature. They have the ability to change their blood flow, allowing them to keep their blubber layer cool and their deep body core warmer. On land, walruses risk overheating because of this feature, but they rest a great deal on land as it uses less energy to stay warm than swimming in the icy waters. Arctic foxes have thick coats of fur that are able to hold a layer of warm air around their body to help maintain a normal core body temperature. Arctic fox have developed small ears and a small nose, which aids in heat preservation. Their thick fur coats even cover the bottom of their feet. Adaptation for arctic animals includes white fur. Polar bears, Dall's sheep, Peary caribou, and some gyrfalcons are naturally white in color. Some turn white in the winter months, such as the arctic hare, ermines, lemmings, arctic fox, and ptarmigans. This helps the animals blend in with their environment, making it easier to hide from dangerous predators. White fur also keeps the animal warmer because it reflects body heat back toward the body.

People of the Arctic

Inuit, Inuk, Inupiat, Chukchi, and Nenet are all Indigenous peoples of the Arctic. Transportation, shelter, hunting, and fishing have all changed with the advancement of technology. Snowmobiles and trucks are now used, instead of foot and dogsled traffic. Umiaks, which are large boats used by the people of the Arctic, are still used today, although most likely they are powered by a gas outboard motor. Hunters can be seen using both harpoons and telescopic rifles. Modern grocery stores are also available, a modern addition. Many people think of an igloo as the primary housing for this region, but people today live in wooden houses with central heating. Igloos are still used as shelters for hunting trips. Established in 1960, McGill Arctic Research Station (MARS) is located at Expedition Fjord, Nunavut, in the Canadian High Arctic. MARS is one of the longest-operating field research facilities in the High Arctic. Vital to the understanding of the Earth's polar biomes, this facility's goal is the understanding of physical and biological processes in cold polar desert and glacierized environments. Current research includes glaciology, climate change, permafrost hydrology, geology, geomorphology, limnology, planetary analogues, and microbiology.

Global Warming

Global warming is a threat to the polar deserts. The accumulation of dangerous greenhouse gases trap heat and light within the Earth's atmosphere. As a result, the temperature is rising on land and sea. The pollution causing this process has actually eroded portions of our ozone layer. This layer protects the Earth from the harmful rays of the sun. The first hole in the ozone layer was noted in 1985 over Antarctica, and another was found later over the Arctic. As a result, scientists have noted that the Arctic is shrinking, permafrost is melting, glaciers are receding, and sea ice is disappearing. The ice on Greenland is melting, and the meltwater is slowly raising sea levels. The polar ice cap is said to be melting at the rate of 9 percent per decade, and Arctic ice thickness has decreased 40 percent since the 1960s. While Antarctic ice is growing due to increased snowfall from warmer air that holds more water vapor, this net increase is less than the net loss in Arctic ice; the global balance remains a net loss of ice. In turn, low-lying coastal areas are disappearing underwater. These changes are expected to impact ecosystems around the world.

With a warmer climate, forests are predicted to expand northward into the arctic tundra, and the arctic tundra will expand into the polar desert regions. Warmer climates will also change the growth patterns of plants, as the climate will support the growth of taller and fuller varieties. The expectation is a smaller tundra, reducing breeding areas for birds and grazing animals of the region. Changes in bird, fish, and butterfly species have already been noted in some areas. The Arctic presently supports more varieties of mosses and lichens than anywhere else in the world. With an increased temperature, this number will likely decrease. Insects, diseases, and weeds are likely to increase throughout the Arctic as the temperatures gradually warm. The shifting of both plants and animals species northward is expected to increase, thus changing the current ecosystems.