Antarctica

The Frozen Continent

December is well underway now. Christmas will soon be upon us. The days have shortened and the temperature has fallen. Many parts of the UK have already seen their first major snowfall of the season. But come spring, this cold, dark time of year will almost seem like a distant memory. So spare a thought for those animals that live in really cold parts of the world, such as Antarctica and the Arctic. For the hardy creatures inhabiting these two snow- and ice-covered regions around our planet’s poles, the cold and the dark is their entire life. There is little respite. They either deal with it, or they die.

Antarctica in the far south is the coldest place on Earth. With an average temperature of -12°C at the coast and around -60°C further inland, this unforgiving landscape of ice is one of the toughest places in the world to live. Even in the height of summer, the temperature rarely rises above freezing. During winter, depending on how close you get to the geographic South Pole, there may be six months of almost total darkness where the sun does not rise at all, owing to the Southern Hemisphere being tilted away from the sun on the Earth’s annual orbit. The temperature can plummet to -80°C or below, and gale-force winds batter the frozen land, causing violent snowstorms that can last for days. If you threw a cup of boiling water into the air, it would freeze into a puff of ice crystals before it even reached the ground.

In this article, we’re going to look at some of the animal inhabitants of Antarctica and how they survive in this icy wasteland. But first, what makes Antarctica so unbelievably cold? And how is it different from the Arctic at the opposite end of the planet?

What is the difference between Antarctica and the Arctic?

If you stand at the North Pole – the most northerly point on Earth – you are not standing, as you might reasonably assume, on a frozen landmass, but on a frigid ocean covered in ice a couple of metres thick, encircled by the mighty continents of Europe, Asia and North America. Between you and the nearest solid land, at the northern tip of Greenland, there is over 710 km of sea ice. This can drift by as much as 40 km a day, which is why no permanent marker can be used on the ice to mark the exact North Pole. To determine that you are really there, you must use a GPS reading or dive down to the seabed, where, in 2007, Russians planted a rust-proof titanium flag.

Antarctica in the south may resemble the Arctic in many ways, but the two are, in fact, polar opposites – pun intended. Rather than being a frozen sea surrounded by land, Antarctica is a frozen continent surrounded by the tempestuous Southern Ocean. Almost the size of Russia, it is a largely white, flat wilderness that extends in every direction to the horizon, with little to break up the monotony.

Ice defines almost all of Antarctica. This huge continent contains 70% of the planet’s entire supply of fresh water, but virtually all of it is locked away as ice, forming a layer that is 1.6 km thick on average. The further inland you go, the thicker the ice becomes. In some places, it may be over 4 km thick, compacted over hundreds of thousands of years. Entire mountain ranges as tall as the European Alps have simply been swallowed by ice. Unlike in the Arctic, where much of the snow blanketing the land melts in summer, revealing a brown and green tundra, Antarctica never thaws. This is just as well, for if the enormous Antarctic ice cap completely melted, global sea levels would rise by as much as 60 m, drowning all of the major coastal cities on the planet.

At the geographical South Pole, there is a stake in the ground and a small sign, which records the respective days that Norwegian Roald Amundsen and Englishman Robert Falcon Scott reached the pole in the early 20th century, followed by a short quotation from each man. Amundsen and Scott led separate teams that raced to become the first to reach this extreme point on the globe, an achievement that was regarded as the ultimate in human endeavour and endurance, and a source of great national pride. The Norwegian team arrived at the South Pole on 14 December 1911, just over a month ahead of the five men in the British party, who all perished on the return journey, a mere 18 km from a depot with food rations. The Amundsen-Scott South Pole Station, named after the two explorers, was built at the South Pole in 1956 and has been continuously occupied by scientific researchers and support staff ever since.

However, the polar ice sheet in Antarctica is moving at a rate of roughly 10 m per year. This means that the base has been slowly travelling away from the precise site of the pole and is now over 180 m from it. To compensate for this continuous movement of ice, staff from the research station reposition the stake and the sign designating the exact South Pole each New Year’s Day.

Both ends of the Earth are extremely cold for several reasons. The first is that the sun, even during the summer when it spends months above the horizon, circling permanently in one long six-month day, remains low in the sky. It cannot produce the burning midday heat of an overhead sun experienced elsewhere in the world. Also, due to the position of the poles on our tilted planet, sunlight strikes them at an oblique, glancing angle. This means that the sun’s energy, as it hits the land, is spread out over a much larger area than at the equator, greatly reducing its intensity. And then there’s the fact that most of the radiation reaching these great white icecaps is reflected back into space without being transformed into heat.

But this is true at both poles. So why is Antarctica even colder than the Arctic? Why does the temperature at the South Pole, even in the height of summer, rarely climb higher than -25°C, which is colder than many midwinter days at the North Pole?

The Arctic is just a relatively thin crust of ice, and the constant presence of the ocean below provides comparative and continual warmth. In addition, high-pressure systems that form each summer over Russia and North America spill warm air north over the region. Antarctica, on the other hand, is surrounded by the cold, violent Southern Ocean – the stormiest on the planet – and is completely isolated from any other large landmass. Thanks to its massive icecap, Antarctica is also the highest continent on the planet and, like anywhere else on Earth, increased altitude causes a decrease in temperature. With every 100 m you climb, the air temperature drops by 1°C – and the surface at the South Pole is 2,900 m above sea level.

Antarctic Animals

Antarctica is extremely hostile to living things. It is the coldest, windiest, and, surprisingly with all that ice, the driest continent on Earth. Beyond humans, the geographic South Pole is practically devoid of life. No animals or plants live there permanently, for although the Amundsen-Scott South Pole Station is continuously occupied, nobody calls it their full-time home.

Very occasionally, off-course skuas and snow petrels fly over the South Pole. The snow petrel is an almost pure-white dove-sized bird that, despite being so small and seemingly delicate, is one of the hardiest animals around, breeding exclusively in Antarctica. In fact, the snow petrel (along with the south polar skua) nests further south than any other bird in the world. These nest sites are often on remote spires of bare rock protruding from the ice – the exposed summits of massive mountain ranges that, for the most part, are completely submerged under the vast depths of Antarctica’s colossal ice sheet. Because bare rock is at such a premium on mainland Antarctica, snow petrels may be forced to nest up to 440 km from the nearest ocean, which means a very, very long commute to catch food.

As you travel further north from the South Pole, more life can be found, especially around the coast, but there are still so few plants and animals here that it makes the Arctic, with its polar bears, herds of reindeer, and its many thousands of migratory birds, look like a hotspot of biodiversity by comparison. On the very outer rim of the continent – and, in particular, the Antarctic Peninsula, which stretches far to the north and so enjoys milder weather – a few small plants cluster around rare pools of fresh water, which are usually caused by melting ice. Jungles of hardy moss, lichen and liverworts provide a home for several types of tiny invertebrates, most no bigger than a pinhead. Many of these minuscule creatures have antifreeze in their blood that enables them to survive extreme cold snaps. Most feed on the thick carpet of moss, but there are also carnivorous mites and springtails that prey upon the grazers. It’s Antarctica’s version of the Serengeti – though you’ll need a microscope to witness it.

The little land vegetation that can survive in Antarctica is so meagre that it cannot provide food for animals of any real size. As such, almost all larger creatures that live here must derive their sustenance, directly or indirectly, from the sea. The cold Southern Ocean contains more dissolved oxygen than warmer waters and is therefore rich in floating algae. These are eaten by immense swarms of krill, which are in turn eaten by fish, penguins, seals, and even whales.

Virtually all of Antarctica’s birds are based around the sea. Many, indeed, are pelagic wanderers that only come to land to breed. Of these birds, only the emperor penguin – the largest of all living penguins, standing over 100 cm tall – manages to stay throughout the viciously cold Antarctic winter. Even then, it is restricted to the edges of the continent and leaves when spring returns.

In fact, although the stereotypical habitat of all penguins is probably the South Pole, only the emperor and the smaller Adélie penguin make this icy continent their true home (three other species – the chinstrap, gentoo and macaroni – breed on the tip of the Antarctic Peninsula, where conditions are less harsh). This is because virtually all penguins require, at the very least, rocks to lay their eggs on – and since only 2% of Antarctica is ice-free, even in the middle of summer, this frozen landmass isn’t really a suitable place for them to breed. The emperor penguin, however, is unique. It is the only bird in the world that lays its eggs directly onto the ice itself – although said eggs are quickly manoeuvered onto the top of the male’s feet to be incubated.

No native land mammals live in Antarctica either and, with the sole exception of the Weddell seal, all of its marine mammals head north each winter as the sea begins to freeze. The Weddell seal spends most of its time underwater; it can hold its breath for up to 80 minutes at a time and is capable of diving down to 600 m looking for squid and fish. Living under the ice helps it stay warm because, relative to conditions on land, the water is a balmy -1.8°C. On the downside, it must keep its air holes open using its teeth, rasping away at the ice. This, however, wears its teeth down. Eventually, they are worn so badly that the seal either starves because it can no longer catch fish, or it drowns because its breathing holes freeze over. Unsurprisingly, Weddell seals have relatively short lifespans – half those of most other seals.

Since all of Antarctica’s mammals and birds are based in and around the sea, or are only seasonal visitors, it means that the continent’s largest permanent native land animal is a species of midge called Belgica antarctica, which is just a few millimetres long. The only free-living insect to live on the Antarctic mainland itself, this tiny fly is wingless – an adaptation to prevent it from being blown away by strong winds. It can survive at -15°C by internally accumulating sugars to act as a natural antifreeze and by dehydrating itself so that ice crystals cannot form in its body and rupture its cells. This midge spends two years as a larva, feeding on terrestrial algae and mosses and building up enough energy for reproduction, but its adult life lasts only a week or so – just enough to find a mate, lay eggs, and then die [1].

The Edge of Life

Believe it or not, most of Antarctica is technically a desert. A desert generally refers to an area of land that has a lack of ground vegetation and gets, on average, less than 250 mm (10 inches) of rain or snow a year – it doesn’t have to contain undulating landscapes of sand dunes or cacti. And since Antarctica’s atmosphere is so dry, surprisingly little snow falls here – only around 166 mm per year, on average. Of course, due to the extreme cold, any snow that does fall tends to linger.

However, one part of the continent – the ice-free McMurdo Dry Valleys – contains areas that haven’t experienced precipitation for over a million years. This makes it by far the driest place on the planet.

The McMurdo Dry Valleys form the largest contiguous area of ice-free land in Antarctica. They are comprised of around 4,800 km² of rocky canyons carved out by long-retreated glaciers. The Transantarctic Mountains, which stretch 3,200 km across the continent, prevent the flow of ice from the massive East Antarctic Ice Sheet from reaching these valleys. Exceptionally strong winds, blowing down off the ice at speeds of 200 mph, compress as they descend, generating heat. This warm, dry wind evaporates all moisture in the air, thus giving the McMurdo Dry Valleys their name. On the very rare occasions that snow does fall here, it is evaporated by the wind so that scientists have reported seeing it descending but never reaching the ground. When explorer Robert Falcon Scott discovered the area in 1903, he described it as a ‘valley of death’.

But these valleys aren’t completely dry. In fact, they’re one of the few places in Antarctica where you can hear the sound of running water. In the Wright Valley, you can find Antarctica’s longest river, the Onyx, although admittedly it only flows for a few weeks during the brief Antarctic summer. This ephemeral river runs for 32 km and empties into Lake Vanda. Though covered year-round by a transparent ice sheet up to 4 m thick, the water at the bottom of Lake Vanda is 23°C and is ten times saltier than seawater. Just 9 km west of Lake Vanda is another body of water, the Don Juan Pond, which is so salty that it can remain liquid even at temperatures as low as -50°C.

These remote, ancient valleys are considered the closest of any terrestrial environment to the planet Mars. The floor is covered with extraordinary natural sculptures, created over thousands of years by the same winds that help keep these valleys free of snow. In 2013, a team of researchers tested a drill designed for sampling on Mars in the permafrost in the driest parts of this region, in order to examine the microbial population. Absolutely no living organisms were found in the permafrost, making it the first location on the planet visited by humans with no active microbial life.

That is not to say that all of the McMurdo Dry Valleys are completely lifeless, though. In Lake Vanda, microscopic algal blooms have been recorded. Some photosynthetic bacteria have also been found living in the relatively moist interior of the rocks themselves. And anaerobic bacteria – those that do not require oxygen for growth – are known to live in sub-zero temperatures under a glacier, without air or sunlight. This is surely the very edge of life on our planet.

Antarctica is one of the last true wildernesses on our planet, but it is also a land of extremes. To survive in such a demanding environment, animals must be extraordinarily tough and versatile. There are no southern comforts for organisms clinging to life here. Those few that embrace this icy world have few competitors, but as a price, they must endure one of the most hostile and forbidding places on the planet.

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[1] The Antarctic midge B. antarctica may be the southernmost free-living insect in the world, but Antarctica’s only documented flea, Glaciopsyllus antarcticus, has been discovered further south because it is a parasite that lives on seabirds such as fulmars and petrels. But whereas this flea stows away on the skin of warm-blooded animals, the Antarctic midge survives the hard way – exposed to the elements.