ANTARCTICA IS THE COLDEST, HIGHEST, DRIEST, WINDIEST PLACE ON EARTH!
Only about two percent of Antarctica peeks through the thick sheets of ice that blanket the continent. In the winter, the lowest recorded temperatures (without wind chill!) have reached -89°C (-129°F). The continent averages 2.4 kilometers in height (1.5 miles) above sea level, making it 1.5 kilometers (almost a mile) higher than the global average land height! Each year the South Pole receives less than an inch of water......in the form of snow, of course! This amount of precipitation is similar to that of another desert, the Sahara! Katabatic winds, reaching 300 kilometers per hour (185 miles/hour), blow out of the continental interior and make the Antarctic coastal regions rather breezy.
Other than being a cool place to go, why should we care about Antarctica? Antarctica is an important part of Earth's system. By acting as a global heat sink, it helps control our climate and weather. The stability of the Antarctic ice sheets is of concern to those living in low-lying areas; they contain enough water to raise global sea level almost 70 meters. Antarctica holds 70% of Earth's freshwater, and 91% of Earth's ice! Antarctica influences our global ocean. Cold, dense, oxygen-rich waters originates in Antarctica and replenishes the ocean's supply of bottom water, helping to drive ocean circulation. The sea surrounding Antarctica supports marine life from tiny ice-dwelling algae to the great whales. Through investigations of Antarctica we will develop a better understanding of how this vast, ice-covered continent responds to environmental change. This knowledge will better enable us to predict the response of Earth's climate systems to future changes.
Antarctica is located in the Southern Hemisphere (the half of the globe that is south of the equator). The continent overlies the South Pole and covers 13,824,000 square kilometers (5,400,000 square miles). It is the fifth largest landmass on the globe. Early Greek geographers hypothesized the existence of Antarctica well before anyone actually saw the continent. They believed that a landmass must exist at the bottom of the world to balance the land in the Northern Hemisphere. They called the mythological land "Antarctica," which means "opposite the Arctic." No one set foot on the continent until John Davis went ashore on the Antarctic Peninsula in 1820.
Antarctica is at the "bottom" of the world. Many maps may not even show the continent and most do not show it well. Antarctica is about 30% larger than the United States. Antarctica can be divided into three parts, East Antarctica, West Antarctica, and the Antarctic Peninsula. Think of Antarctica as an elephant's head.......East Antarctica would be the ear, West Antarctica would be the face, and the Antarctic Peninsula would then be the trunk. Two thick sheets of ice cover Antarctica. The East Antarctic Ice Sheet is the biggest. The smaller ice sheet covers West Antarctica. These two ice sheets behave very differently, as you will find in the section all about ice sheets. Tips of the Transantarctic Mountains make up much of the "continent" peeking through the thick ice sheet. The Transantarctic Mountains divide East and West Antarctica. These mountains rival the North American Rocky Mountains in height! Yet, the ice sheet covers all but the mountain tips.
Sorry, there are no polar bears or Eskimos in Antarctica! Penguins and seals are the most familiar "land" creatures. Making a living in Antarctica means being creative with survival strategies! Antarctic organisms have adapted to the extreme conditions in a variety of complex and innovative ways. Most organisms live in or at least get their food from the sea. Amazingly enough, there are some tough customers that depend entirely on what they can glean from the harsh, frozen continent!
LIVING ON THE LAND
The land flora includes algae, mosses, and lichens. Two species of flowering plants live in the "warmer" Antarctic Peninsula region. Lichen actually are a commensal relationship between fungus and algae. The fungus adheres to the rock, producing a moist mesh to which the algae attach. The algae in turn make food for the fungus through photosynthesis. Lichens prefer dry regions and adapt quite well to cold climates. Antarctica is ideal for them because there is little competition. During the cold, dark winters, lichens slow down their metabolism.
The Dry Valleys of Antarctica as a thriving ecosystem?! You bet! The Dry Valleys had long been considered a barren polar desert. On closer look, however, the Valleys are home to a thriving ecosystem! The rocks themselves host communities of tiny organisms such as bacteria, cyanobacteria, and algae. The rocks provide protected pockets of air that also hold moisture from rare snowfalls. The light color of the rocks allows some sun to penetrate. So even in these extreme environmental conditions, some organisms make a living!
Tiny invertebrates such as mites, springtails, and midges comprise the fauna that live exclusively on land. The largest of these is the flightless midge, reaching a whopping 12 mm (slightly less than 1/2 inch)! All of these little arthropods dwell in the nooks and crannies of rocks and soil, dining on bacteria, fungi, algae, and each other! Many survive the freezing temperatures because their body fluids contain glycerol. Glycerol is an antifreeze that allows the organism to live in temperatures as low as -35C (-30F). A few of the critters actually can survive freezing!
Note: What about people? No indigenous human populations ever have occupied Antarctica. Humans are temporary visitors. Only a few thousand people visit the Antarctic continent every year; approximately 4000 for scientific purposes, and 3000 as tourists.
LIVING BETWEEN LAND AND SEA
While seals and penguins spend part of their time on land or on the sea ice, the diner gong sounds in the sea. The ocean is vital to the lives of almost all organisms living in Antarctica. Seven species of penguins live in the Antarctic. These birds never soar through the sky - instead, their flippers are modified wings adapted for flying through water! Penguins keep warm because they have a dense layer of waterproof feathers that traps a layer of air next to their skin. They also have a thick layer of fat between their skin and muscles. If anything really troubles a penguin on a sunny day, it is overheating! Penguins cool by ruffling their feathers, stretching their flippers, and exposing their feet.
Penguins do not move quickly on land, but, then again, they do not need to. Remember that polar bears are far away up north! Adult penguins have no predators on land, although juveniles might fall prey to skuas (a type of seabird) that attack eggs and chicks. However, when penguins enter the sea to feed themselves, they, in turn, might be eaten by one of several predators. Penguins are a tasty treat for killer whales and even for some types of seals! Where does a penguin go when winter arrives? Many of the penguins migrate north with the pack ice, not returning to a coastal rookery (nesting ground) until spring narrows the ring of pack ice around the continent. Only the emperor penguin males stay on the inner pack ice to incubate an egg through the long, cold winter, huddling together for warmth, and with nothing to eat! With spring, the female returns from feeding in the open ocean to assume charge of the newly hatched chick (A much skinnier Dad quickly heads off for the oceanic feeding grounds). The cycle of the emperor is timed such that the eggs are laid in the fall and hatch in the early spring. This allows rapidly growing chick to take full advantage of the abundant spring and summer food. Penguins build and squabble over nests and nesting material. Twigs and straw being absent, pebbles are the building materials of choice!
Note: Are there penguins in the Arctic? No! Those pictures of Santa Claus surrounded by tuxedo'ed sea birds are merely artistic license. There are no penguins in the Northern Hemisphere. There are similar (although not closely related) birds, though. The Northern Hemisphere auks fill an ecological niche comparable to penguins' at the other end of the planet.
Penguins are not the only seabirds in Antarctica. Various other birds, such as petrels, terns, and albatrosses live here at least part of the year. The Arctic tern visits Antarctica each summer after flying down from the North Pole! This bird has the longest known migratory route. It lives most of its life in sunlight because it chases summer from one end of the planet to the other!
Antarctica has its share of seals, including Crabeater, Leopard, Elephant, Weddell, and Fur seals. Like penguins, seals cannot fly, but they too are excellent swimmers. Seals have thick layers of fat to keep them insulated against the cold Antarctic air and ocean. Their diets are as varied as their lifestyles. All get food from the ocean, whether the food is penguin, squid, fish, or shellfish. Weddell seals are the only seals that live in Antarctica year round. Other seals follow the pack ice edge northward as winter begins and the sea ice grows around the continent. Weddell seals spend their winter in the ocean beneath the sea ice, maintaining a breathing hole by gnawing through the ice to the air above. Because the seals have no land predators in the Antarctic, the pups are dark in color. Arctic seals are born with white fur to blend in with the snow so that they will not so easily attract the attention of hungry polar bears!
Note: Why doesn't the South Pole have polar bears? Antarctica split apart from the other continents and drifted into its present isolated location long before bears came on the scene. Polar bears might be able to survive around the fringes of the Antarctic continent (in conditions not unlike their own, Arctic environment), but the penguins would not be happy. The Antarctic Treaty, however, clearly states that the Antarctic environment should be preserved, and therefore introduction of exotic species is not permitted.
LIVING IN THE WATER
In contrast to the landmass, the ocean is teeming with many different forms of life! Although the water is cold, it is warmer than the land. It also offers a relatively constant environment, making it easier for organisms to adapt and even thrive. A major feature of the marine realm is the seasonal pack ice zone that greatly expands around the continent each winter and shrinks back each summer. This environment supports the greatest diversity of species and the largest numbers of each species of any region in the Antarctic!
Plankton is tiny marine organisms carried about by ocean currents. Phytoplankton are minuscule plants whose importance is much larger than their size - they are the base of the food chain on which every animal's dinner ultimately depends! In spring and summer they can multiply so rapidly ("bloom") that large patches of the ocean look like thick soup. In the winter it is a different story, because there is no sunlight for photosynthesis. The phytoplankton must hang on and wait for the sun to return. Some phytoplankton even live inside the sea ice! They are concentrated on the underside of the ice, where they can live within sheltered channels in the ice while not being too far from the nutrient-rich seawater. The base of the sea ice is commonly brown in color due to plant pigments from algae!
Zooplankton are tiny animals that cannot out-swim ocean currents and so are carried along in them. They eat phytoplankton - and get eaten by larger animals! Krill are plentiful Antarctic zooplankton that are concentrated within the seasonal ice zone. The largest of these shrimp-like crustaceans range from 2.5 to 5 cm (about 1 to 2 inches). The Southern Ocean contains 440 to 715 tons of these tiny animals, and their importance in the Antarctic food chain cannot be overestimated! Many species of fish, seabirds, squid, seals, and even huge whales depend on these zooplankton as their sole food source. Hence, just three simple steps (the first two being phytoplankton and krill) define large parts of the Antarctic food web. Several other species, including penguins, also depend on krill as a significant portion of their diet.
Many fish keep their body temperatures close to that of the seawater they live in, so as not to waste energy by generating heat. Some Antarctic fish even keep their body fluids below the freezing point in a supercooled state! They can do this as long as there are no ice crystals or other nuclei around which ice can form. Other fish manufacture their own antifreeze in the form of glycopeptides. Perhaps the most unusual type of Antarctic fish is the ice fish family. These fish have white gills due to the complete absence of hemoglobin (red oxygen-carrying pigment in blood). In this fashion they are unlike all other vertebrates. Their blood carries only 10% of the oxygen relative to red-blooded fish in the same environment. To increase their oxygen-carrying efficiency, they have a higher blood volume and a larger heart with a faster beat.
Whales are the largest mammals in the world. Blue whales are the largest animals that have ever lived, averaging 30 meters (100 feet) in length and 180 tons in weight! All Antarctic whales are summer visitors. They come to feed in the rich Antarctic waters then migrate northward to breed in the tropics or subtropics. Killer whales are abundant at the ice edge around Antarctica where they feed on seals and penguins. Minke whales, the smallest of the baleen whales, are the most numerous in Antarctica, with a population of about 750,000. They are about 8 m (26 feet) long and weigh 6 to 8 tons. Baleen whales eat only krill and phytoplankton - they take great mouthfuls of the sea and strain out their food by expelling the water through special fringed plates in their mouths. Before whaling, there where about 200,000 blue whales, but now these slow-breeding mammals number about 1000. Pods of Orca (killer whales) can often be seen sporting around the ice edge in the summer months. These pack hunters work to herd other animals, including penguins, for feeding purposes. The ocean basins of the world vary little in terms of bottom water characteristics, so the sea floor around Antarctica is not much different by depth zone than that in other regions. Some forms of sponges and corals live here! A major controlling factor in who sets up housekeeping where is the composition of the sea floor - how muddy or rocky it is.
A few features are unique to Polar Regions. In areas less than 15 m (about 50 feet) deep the sea floor community must contend with the annual formation of pack ice that scrapes the bottom each year. Organisms migrate to deeper water in the winter and return to their shallower summer home when the ice is no longer threatening eviction orders! Another danger in water less than 30 meters (about 100 feet) deep is anchor ice. It forms at the sea floor, enveloping any organisms that happen to be living there. Eventually it wrenches free of the bottom, carrying the unfortunate creatures with it! In deeper waters, bottom communities can be churned up by the passing of large icebergs that occasionally drag over the sea floor. The largest ones can gouge the ocean bottom in water 500 meters (about 1640 feet, or 1/3 mile) deep!
LAKES IN ANTARCTICA
There are lakes containing liquid water in frigid Antarctica! They range from freshwater to saline (salt water), and they are ice covered for most of the year. Among the creatures calling them home are algae, bacteria, and fungi. Solar energy keeps the at least some of the water in liquid form, and a few lakes are aided in their existence by geothermal warmth rising through the land below. A huge lake is currently being remotely studied under Vostok Station in East Antarctica. Just imagine a body of water over 100 miles long trapped for thousands of years between the warm continent below and the thick cold ice above! Seasonal streams are associated with melting of ice during summer on land around the fringes of the continent and on Antarctic islands. While these streams are active, bacteria and algae take full advantage of the situation!
Antarctica has two seasons - a very brief summer and a long cold winter. At the South Pole, there is only one period of sunlight each year, and it lasts six months! It's a great place to avoid vampires - at least for half of the year. The other half is a different story, because the sun does not come above the horizon for the remaining six months. With distance northward from the South Pole there are increasing (but still very short!) periods of sunlight during winter (and night during summer). Still, the lengths of summer days and winter nights are vastly exaggerated compared to what we are used to at lower latitudes!
The seasons in the Southern Hemisphere are opposite to those in the Northern Hemisphere, so summer in Miami, Florida occurs at the same time as winter in Melbourne, Australia (and Antarctica). The tilt of Earth's axis causes the reversal of the seasons. Each hemisphere receives the most solar energy when it is tilted toward the sun, so the time during which the Northern Hemisphere and Southern Hemisphere receive the most energy differs. Seasonal light conditions in the Arctic are the same as in the Antarctic (although the seasons occur at different times) - the summer is filled with long days and the winter has long nights.
The sun doesn't get much of a chance to warm our poles compared to, say, the equator! We've just discussed how Antarctica receives little or no sunlight for half the year. There are other reasons, too. Due to Earth's curvature, our polar regions receive limited solar energy. Earth's surface intercepts the greatest amount of solar radiation where it is directly beneath the sun (at or near the equator). At more oblique angles, incoming radiation spreads out and covers more area. It also travels through a thicker layer of atmosphere, so more gets absorbed or reflected before it reaches the ground.
Of the solar radiation that reaches Antarctica, most of it bounces off again! Ice is an extremely good reflector of sunlight. How well Earth's surface reflects solar radiation is called its albedo. The high reflectivity of ice and snow reduces their effective heating. Here's a comparison: ice reflects 80 - 95% of solar radiation (meaning only 5 - 20% is available for warming), while grassland reflects 30 - 40%, and a conifer forest, only 10 - 15%. Over the course of a year, Antarctica actually loses more solar energy than it retains. Only for a short time at summer's height is there a net energy gain. Antarctica would be even colder if it did not receive heat from other parts of the globe. Warm, moist air rises at the equator and travels toward the poles. On its way, its water vapor condenses, giving up heat. This process is an essential part of maintaining Earth's heat balance!
Antarctica has various types of ice depending on where you are. Here are the general types.
Ice sheets are the largest accumulations of glacial ice. They form from accumulating snow and completely blanket the underlying land, hiding its topography from our view. Two ice sheets cover Antarctica, the larger East Antarctic Ice Sheet and the smaller West Antarctic Ice Sheet.
Ice shelves are floating masses of glacial ice at the edges of the continent. The biggest is the Ross Ice Shelf, which is about the size of Texas. Ice shelves can occur in embayments where ice flow is convergent (coming together from many places on the continent).
Ice streams and outlet glaciers are the fastest moving parts of ice sheets. They are the fastest moving part of the ice system and help to drain ice away from the ice sheet. If the streams of ice are separated by exposed topography, such as a mountain divide, the streams are called outlet glaciers. If the streams of ice are not separated by topography, but their edges touch, they are called ice streams.
An ice tongue is a glacial mass extending across the sea surface. The ice may be channeled through a valley. Ice tongues are narrow, long, floating ice features. The Drygalski Ice Tongue is the largest on the continent.
Icebergs are pieces of floating ice that break off, or calve, from ice shelves, ice tongues, and the edges of ice sheets. The form and size of icebergs varies tremendously. One iceberg, about the size of the country of Belgium, was sighted in 1956! Iceberg B-15, calved from Ross Ice Shelf in 2000, was roughly twice the size of the state of Connecticut! It has traveled approximately one kilometer per day (a little over one half of a mile per day) and has broken into numerous smaller icebergs but very large pieces are now being instrumented for study.
Sea ice freezes from seawater and grows to cover large areas of polar oceans during winter. It mostly melts away again each summer. Each winter, the growth of sea ice around Antarctica essentially doubles the area of the continent! The freezing process "squeezes" out the salt content and this leads to dense, cold currents of water flowing away from Antarctica into the "oceanic current network" that helps distribute heat around the world.
Comments, questions? Contact the source of most of this handout at:http://www.glacier.rice.edu/ or try http://www.nsf.gov/od/opp/antarct/start.htm