Antarctica: A Continent of Ice

All you need to know about the climate, geography, topography, ice sheets, glaciers, and sea ice of this incredible continent of Antarctica - half the size of Africa - as well as its rich marine biodiversity.
Thwaites Ice Shelf edge
Thwaites Ice Shelf edge. The blue areas of ice are denser, compressed ice. Photo: © NASA/James Yungel

Antarctica is the coldest place on Planet Earth, with temperatures dropping as low as minus 98°C (minus 144°F). It’s also massive, covering an area of 14,200,000 square kilometers (5,500,000 sq mi) – more than one and a half times the size of the United States.

The Antarctic ice sheet covers 99.6 percent of the continent, averaging 1,900 m (6,200 ft) in thickness, with a maximum of 4,776 m (15,669 ft). 1 Only a few mountain peaks – known as nunataks – are visible above the ice.

Antarctica has the largest glaciers and ice shelves, and its overall ice mass comprises 70 percent of Earth’s freshwater. Along with the Arctic and certain alpine high-altitude regions, the Antarctica comprises Earth’s cryosphere, the planetary store of frozen water.

The largest of Earth’s polar biomes, Antarctica is surrounded by sea ice in winter, which can exceed 18 million sq kilometers (7 million sq mi) at its maximum extent. However, like the Arctic region in the northern hemisphere, the Antarctic is feeling the effects of climate change, with higher temperatures and greater ice melt. 2 Indeed, a new study warns that the South Pole is warming nearly three times faster than the global average. 3

There is no native population in Antarctica unless you count its 5 million penguins. All entry to, and activities on, the continent are regulated by the Antarctic Treaty (1959), which is agreed to by all countries operating there. Above all, Antarctica is a place for science, especially climate science, although the 10,000 scientists who work in Antarctica during the summer carry out scientific research in a wide variety of physical and biological sciences.

Geography

Antarctica is a continent which occupies almost all of the Antarctic Circle. It is traditionally divided into three sections: West Antarctica, East Antarctica, and the Antarctic Peninsula – the first two being divided by the Transantarctic Mountains.

All three areas vary considerably from each other in topography. The Antarctic Peninsula is actually a string of islands (all covered by the ice sheet) separated by deep channels. West Antarctica consists almost entirely of bedrock that is below sea level, except for a small portion of higher land east of the Getz ice shelf. East Antarctica, by comparison enjoys a thicker ice sheet, and its bedrock has a higher mean elevation than the rest of the continent.

Antarctica is encircled by the Southern Ocean, with the Weddell Sea in the north, the Amundsen Sea in the west and the Ross Sea to the south. In winter, more than half of the Southern Ocean around Antarctica freezes over, forming an almost impenetrable barrier of sea ice covering an area about one and half times the area of the continent. Although this sea ice measures only about one meter thick (and melts during the summer), it has a significant effect on oceanic and atmospheric circulation. 4

Antarctica’s nearest neighbors include: Tierra del Fuego, Argentina (1,130 km); Punta Arenas, Chile (1,370 km); Hobart, Tasmania (2,609 km); and Christchurch, New Zealand (2,850 km).

Map of Seas Around Antarctica
Map of Antarctica and the surrounding seas of the Southern Ocean. Image: © Rooiratel (CC BY-SA 4.0)

Antarctic Peninsula

The peninsula is covered in ice but mountainous, with peaks rising to over 3,000 m (10,000 ft). They include Mount Castro, Mount Coman, Mount Gilbert, Mount Jackson Mount William, Mount Owen, Mount Scott and Mount Hope, the highest of all, at 3,239 m (10,627 ft). This range is seen as a continuation of the Andes range of South America, with an ocean-floor ridge connecting the two. A similar type of land bridge, known as the Scotia Arc, links the peninsula mountains to those of Tierra del Fuego. A number of the islands around the Antarctic Peninsula contain volcanoes. These are associated with tectonic activity in the Bransfield Rift to the west and Larsen Rift to the east of the Peninsula.

The Antarctic peninsula has a steep elevation gradient, with glaciers flowing into the Larsen Ice Shelf on the peninsula’s east coast. Since the mid-1990s, this ice shelf has suffered a series of breakups. The Larsen A ice shelf collapsed in January 1995; Larsen B ice shelf disintegrated in 2002; and a large section of the Larsen C shelf broke off in July 2017, forming a massive iceberg known as A-68. The iceberg was 160 km (100 miles) in length, covered an area of 5,800 sq km (2,240 sq miles), and weighed one trillion metric tons. The ice shelf originally covered an area of 85,000 square kilometres (33,000 sq mi), but as of June 2020 it occupies an area of approximately 67,000 square kilometres (26,000 sq mi).

The collapse of Larsen A and B has been linked to ongoing global warming, due to rising temperatures on the peninsula. For example, one study revealed that – due to changes in wind patterns exacerbated by climate change – the peninsula warmed by 2.94˚C (5.3˚F) from 1951 to 2004, much faster than the continent as a whole and faster than the global average. 5

Other ice shelves on the peninsula include George VI Ice Shelf, Wilkins Ice Shelf, Wordie Ice Shelf, and the Bach Ice Shelf, as well as the Filchner-Ronne Ice Shelf to the south-east of the peninsula. Most of the outlying islands along the peninsula are blanketed in ice and connected to the peninsula by pack ice.

As the most northerly part of Antarctica, the peninsula has the mildest climate on the continent. In summer, the coasts are the only parts of Antarctica that become ice-free, and the landscape is typical Antarctic tundra with rocks decorated with mosses and lichens.

Glaciers draining into Amundsen Sea Embayment, West Antarctica
Map showing the main glaciers that drain into West Antarctica’s Amundsen Sea Embayment. The ground underlying these glaciers slopes deeper below sea level as it extends inland. Thus, as the glaciers retreat, the warmer ocean water follows, adding further to the melting process. For this reason, glaciologists believe that the disappearance of these glaciers is inevitable, albeit over two centuries or so. Image: Courtesy of NASA 6

West Antarctica

West Antarctica, too, is covered by the West Antarctic ice sheet (WAIS), which is listed as a marine-based ice sheet, because its bedrock lies well below sea level. The volume of the entire Antarctic ice sheet is roughly 25.4 million cubic kilometers (6.1 million cu mi), 10 percent of which is contained within the West Antarctic Ice Sheet. The weight of the ice has caused the bedrock beneath the ice sheet to sink by about 750 m (2,460 ft), the result of a mechanism known as isostatic depression. But West Antarctica boasts the continent’s highest mountain, Mount Vinson, with an elevation of 16,066 feet (4,897 meters). It is situated in West Antarctic’s Ellsworth Mountains, just south of the peninsula.

Much of its ice forms floating ice shelves. These include the huge Ross Ice Shelf, to the south, the Filchner-Ronne Ice Shelf to the north – each about the size of Spain – and the Abbot and Getz ice shelves to the west. These ice shelves help to slow the flow of glacial ice into the ocean. When shelves collapse, glaciers can accelerate significantly. For example, after the collapse of the Larsen B shelf, four of its feeder glaciers increased their speed to between two and six times their original flow rate. 7

Scientists have long described Thwaites glacier as the “soft underbelly of the Antarctic ice sheet”. This is because studies have shown that ice streams like the Thwaites and Pine Island glaciers, that drain into West Antarctica’s Amundsen Sea Embayment, may have entered an irreversible phase of melting. A combination of factors is behind this, including rising temperatures, topography, and geothermal effects, as well as changes in the Southern Annular Mode (SAM), exacerbated by the effects of global warming on the southern hemisphere.

East Antarctica

East Antarctica comprises two-thirds of the entire continent. It is drier and colder than anywhere else in Antarctica, and its underlying bedrock is more elevated than that of West Antarctica. Except for a few areas of coastline, East Antarctica is covered by the largest of the three ice sheets on the continent, whose thickness averages 2,226 meters (7,303 ft) – compared with the WAIS maximum of 1,306 meters (4,284 ft) – although the ice can reach 15,700 ft (4,800 m) at its thickest point. Overall, the East Antarctic ice sheet (EAIS) has about 9 times the mass of the WAIS.

The East Antarctic ice sheet has 7 main domes (high points). Dome A or Dome Argus, located 1,200 kilometres (750 mi) inland is the highest, standing 4,084 m (13,400 ft) above sea level. Dome A is the coldest place on Earth, with temperatures believed to reach minus 98°C (minus 144°F). 8 Roughly 2,400 m (7,900 ft) below the surface of this vast ice dome, sits the Gamburtsev Mountain Range, which is about as big as the Swiss Alps.

Climate

Much of Antarctica is a polar desert, with average annual precipitation (mainly snow) of 200 mm (7.9 in) in coastal regions – where snowfalls of up to 1.2 meters (48 in) in 48 hours have been recorded – but almost none (less than 50 mm per year) in the interior, where no rain has fallen for almost 2 million years. The average snowfall for the continent as a whole is 166 mm (6.5 in). Mean annual temperature is around minus 50°C (minus 58°F), although it averages minus 63°C (minus 81°F) in winter, falling as low as minus 90°C and below. In summer, it has recently (Feb 2020) risen as high as 18.3°C (65°F). 2 Article also says that climate change is heating up Antarctica and the Arctic—the Earth’s polar regions—faster than other regions of the planet.] Winds up to 322 kmh (200 mph) have been recorded. 9

• See also: What’s the Difference Between Climate and Weather?

Why is Antarctica So Cold?

To begin with, the angle of the Sun is always low in the sky, so the sun’s energy disperses over a large area. In regions south of the Antarctic Circle the sun doesn’t rise at all for part of the winter.

Second, most of the sun’s energy is reflected back into space by the albedo effect of the white ice. Unfortunately for those working in Antarctica, because the white surface reflects almost all of the ultraviolet light falling on it, sunburn is a significant health issue.

Thirdly, the comparatively high altitude of the continent depresses temperatures by about 1°C for every 100 m increase in height.

Fourthly, extra strong winds (called katabatic winds) – generated when cold, dense air lying just above the elevated levels of the Antarctic ice sheets is pulled down to the coast by the force of gravity – make the temperature even colder.

Lastly, strong winds and ocean currents tend to flow continuously around the continent in a west-to-east direction, blocking warmer air and water to the north.

Marine Biodiversity in the Southern Ocean

Even though most of the Antarctic landmass is icy and barren, the waters surrounding it are packed with life, beginning with 700 different species of algae, mostly phytoplankton, as well as deep-water bacteria. See also: Marine Microbes Drive the Aquatic Food Web.

However, Antarctic krill (Euphausia superba) – which start out as zooplankton grazing on phytoplankton, before moving up to the next trophic level in the marine food web – are the keystone species of the Southern Ocean ecosystem, and congregate in vast shoals. Krill are a critically important food source for whales, leopard seals, fur seals, squid, many types of fish, penguins, albatrosses and many other seabirds.

A key feature of the Southern Ocean is the upwelling of the nutrient-rich waters of the thermohaline circulation currents that rise up from the depths. It works like this. Strong westerly winds blowing across the surface of the Southern Ocean push water away. Due to a mechanism called ‘Ekman suction’, water then rises up from lower layers beneath the surface, to replace the water that is pushed away. This process is called ‘upwelling’.

Upwelling occurs both along coastlines and in the open ocean. Water that upwells from the depths is extremely rich in nutrients, due to the continuous fall of organic matter (waste products and remains of dead organisms) to the ocean floor. These organic nutrients fertilize surface waters, boosting plankton populations and adding to marine biodiversity and growth. Which is why sites of regular upwelling make excellent fishing grounds.

Upwelling in the Antarctic is strongly influenced by the Southern Annular Mode (SAM), a regional weather cycle that controls the position and speed of the westerly winds encircling Antarctica. When SAM is in positive mode, the winds wrap themselves closer around the continent, which leads to more upwelling. When SAM is in negative mode, the winds recede and upwelling decreases.

Sea Ice in the Antarctic

During the period 1981–2010, Antarctic sea ice extent attained an average winter maximum (in mid/late September) of just over 18 million sq kms (7 million sq mi), and a summer minimum (in late February or early March) of about 2.6 million sq kms (1 million sq mi). In comparison, the Arctic winter maximum averages about 6 million square miles, and the summer minimum 2.5 million square.

Because so little Antarctic sea ice, survives the summer, the majority of it is no more than one year old. It is therefore quite thin – typically, no more than about 1m (3 ft) thick.

Since the late 1970s, the satellite record shows that sea ice extent in the Southern Ocean has varied enormously from year to year, but few of these fluctuations have been statistically significant and the overall trend is fairly flat. For example, in the last decade, Antarctic sea ice extent has achieved both both record highs and record lows. The years 2013, and 2014 witnessed record maximums; 2017 and 2018 saw record minimums. Over the past 4 years, ice extent has been mostly below the 1981–2010 average, although as of April 2020 it is showing a slightly positive long-term trend.

In any event, variations in Antarctic sea ice behavior are believed to be caused mostly by natural variations in weather patterns over the Pacific and Southern Oceans (El Niño-Southern Oscillation and Southern Annular Mode, respectively), rather than by man-made climate change. In other words, while rising air temperatures are having an obvious impact on Arctic sea ice, they have less apparent effect on Antarctic sea ice, although ocean warming is definitely melting the Antarctic ice sheets.

One thing to bear in mind. Intact pack ice in front of an ice shelf protects the shelf from ocean swells. When the sea ice is gone, the shelf is more vulnerable to disintegration. So sea ice extent is an important factor in maintaining the stability of the West Antarctic and Peninsular ice sheets, in particular.

RECENT STUDY

Satellite measurements show that recent increases in Antarctic sea ice up to 2014, were followed by a rapid decrease during the period 2014–2017, resulting in the smallest extent of Antarctic sea ice in the 40-year record. 10 See also: Arctic Sea Ice: How Fast Is It Melting?

This has been confirmed by the EU’s Copernicus Earth Observation Programme which stated that Antarctic sea ice extent reached 12.2 million sq km in June 2019 – roughly 1.4 million sq km (or 10 percent) below the 1981-2010 average for June. This is the lowest sea ice extent measured in June since records began in 1979. 11

Claire Parkinson, leader of the sea ice study cautions against drawing any premature conclusions. “There was a period in the 1970s when the Antarctic also had a huge decrease in sea ice and then increased. So, it could be this huge decrease over a few years (2014-2017) is going to reverse itself,” she says.

So, is this decrease in sea ice caused by our present climate crisis, or not? It’s too soon to say, says Mark Serreze, director of the U.S. National Snow and Ice Data Center. The decline may simply be the result of natural changes, caused by a shift in wind patterns which influence the extent of Antarctic sea ice. To characterize this recent dip as the beginning of a longer-term decline driven by greenhouse gas emissions, is premature.

Is Antarctica Warming?

Yes. Both of the polar biomes – Greenland and Antarctica – are warming. In fact, they are losing ice at a much faster rate than in the 1990s and are on course to attain the IPCC’s worst-case climate change projection. As a result, there is likely to be a significant extra sea level rise by 2100.

These findings are part of a comprehensive study of polar ice conducted between 1992 and 2018 by 89 polar scientists from 50 international organisations, under the auspices of the Ice Sheet Mass Balance Intercomparison Exercise (IMBIE).

Altogether, data from 11 different satellite missions were used, including measurements of the ice sheets’ changing volume, flow and gravity. According to the study, Greenland and Antarctica shed 6.4 trillion metric tons of ice between 1992 and 2017 – pushing up global sea levels by 17.8 millimetres. Of this, 60 percent was due to Greenland ice losses and the remainder from Antarctica.

So, there’s no doubt that both polar regions are warming, and warming faster than the global average. But compared to the situation in the northern hemisphere where Arctic fires are becoming more and more widespread and where permafrost is thawing faster than ever, the Antarctic is responding less rapidly to climate change.

For example, only a small fraction of snow on Antarctica’s enormous ice sheet reaches melting point during the summer. Moreover, Antarctica is encircled by a vast ocean, and shielded by protective winds and weather patterns that help to ward off any large intrusions of warm air or warm water.

Even so, the frozen continent has warmed, and has lost billions of tons of ice in the process. The East Antarctic Ice Sheet has remained relatively unchanged, but air temperatures over the Antarctic Peninsula are definitely rising. This has increased surface melting, and a large proportion of the ice shelf along the east coast of the peninsula has disintegrated following particularly warm summer periods.

The rest of the West Antarctic Ice Sheet remains colder than the peninsula, so any increase rise in summer temperatures has not yet resulted in any significant summer melt. However, new ocean circulation patterns are allowing warmer water to reach the ice fringes along the coast. This warming effect is rapidly thinning the thickest glaciers at their base, and leading them to increase their rate of flow into the ocean. As a result, glaciers in West Antarctica – notably those in the Amundsen Sea Embayment are losing significant ice mass. 12

So while things seem stable for the moment, Antarctica’s future reaction to warming air and ocean could still have worldwide consequences.

References

  1. Bedmap2: improved ice bed, surface and thickness datasets for Antarctica” (PDF). Fretwell, P. et al; (2013). The Cryosphere. 7 (1): 390. []
  2. Antarctica appears to have broken a heat record.[][]
  3. Record warming at the South Pole during the past three decades.” Clem, K.R., Fogt, R.L., Turner, J. et al. Nat. Clim. Chang. (2020). []
  4. All About Sea Ice.[]
  5. The Impact of a Changing Southern Hemisphere Annular Mode on Antarctic Peninsula Summer Temperatures.” Gareth J. Marshall, et al; J. Climate (2006) 19 (20): 5388–5404. []
  6. NASA []
  7. Antarctic Glaciers Accelerate in Wake of Ice Shelf Breakup.” []
  8. Ultra-low Surface Temperatures in East Antarctica From Satellite Thermal Infrared Mapping: The Coldest Places on Earth.” T. A. Scambos, et al; 25 June 2018. Geophysical Research Letters. Volume 45, Issue 12. Pages 6124-133. []
  9. British Antarctic Survey. []
  10. A 40-y record reveals gradual Antarctic sea ice increases followed by decreases at rates far exceeding the rates seen in the Arctic“. Parkinson, Claire L. (26 June 2019). Proceedings of the National Academy of Sciences. 116 (29): 14414–14423. []
  11. Sea ice cover for June 2019.[]
  12. Antarctica is colder than the Arctic, but it’s still losing ice.[]
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