Antarctic Ice

Antarctica contains 90% of the freshwater ice on the planet.

Over 99.5% of Antarctica is covered in ice. 

There is more ice in Antarctica than every other glacier on earth combined.

If all the ice in Antarctica melted, global sea levels would rise by about 200 feet (60 meters).

ANTARCTIC ICE

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glacier calving

Introduction

Transantarctic mountains

Ice Sheet

iceshelf

Ice Shelves

Grease ice

Sea Ice

Transantarctic mountains
Antarctica is a continent of ice. 

From the tallest summits to the deepest valleys, Antarctica is moved, shaped and defined by the ice that envelops it.

INCREDIBLE ICE

Antarctic ice is many things . . .

Habitat

Sheltered habitats under the ice support vibrant ecosystems.

Adelies exiting water

Refuge

At sea, ice provides vital refuge from marine predators.

Weddell seals on iceberg

Respite

Ice floes provide resting places for seals and penguins.

emperor penguin chicks

Breeding

Ice provides a platform for breeding and raising young.

glacier calving

Antarctic ice also plays a critical role in regulating the Earth’s climate.

The Antarctic Ice Sheet covers an area larger than the United States and Mexico combined. Its white surface acts as an enormous reflector, sending heat back to space and keeping the planet cool. 

In winter, seasonal sea ice doubles the area of Antarctica. The growth of sea ice generates dense, heavy water that helps drive deep global ocean currents, which regulate the Earth’s climate. 

LAND ICE OR SEA ICE?

Antarctic ice comes in many forms.

To understand Antarctic ice and how it is changing, we first need to understand the different kinds of ice in Antarctica, how they form, and how they influence the global climate.

Transantarctic mountains

Land ice (also known as meteoric ice) falls as snow, and forms when snow is buried and compressed by layers of snow above. Antarctic meteoric ice includes the Antarctic Ice Sheet and its ice shelves. Some of the ice in Antarctica is thousands of years old and hundreds of feet thick.

Pancake Ice

Sea ice is made of frozen ocean. It forms when the ocean itself freezes over. Unlike land ice, sea ice is generally only a few feet thick. Antarctic sea ice is seasonal, forming each winter and melting almost completely each summer. 

Transantarctic mountains

ANTARCTIC ICE

Land Ice: The Antarctic Ice Sheet

The Antarctic Ice Sheet is the largest mass of ice on the planet. It is much larger than the United States, almost twice the size of Australia and about fifty times the size of the UK. If you spread the Antarctic Ice Sheet across the United States and Mexico, they would be covered in a layer of ice around 7000 feet (over 2000 meters) thick.

Transantarctic mountains
Transantarctic mountains
Transantarctic mountains
Transantarctic mountains
Antarctic tidewater glacier
Antarctic mountains and tidewater glacier

How did the ice sheet form?

Antarctic Ice

The Antarctic Ice Sheet began as a series of small glaciers, much like the ones we see in high alpine regions today. It started to form between 34 and 35 million years ago. At that time, South America and Tasmania, which had been connected to the Antarctica landmass for millions of years, started drifting to the north. The Southern Ocean began to flow around Antarctica like a great oceanic moat. Global temperatures fell and Antarctica was plunged into what some describe as a ‘34 million year winter’. 

With each storm, Antarctica was blanketed in snow. Temperatures were so cold that the snow on the mountaintops never melted, and layer upon layer of snow built up. Over time, the weight and pressure of each snowfall caused the layers of snow below to harden into glacier ice. The glaciers grew, gradually creeping down into the valleys and blanketing the entire continent in a thick mantle of ice: the Antarctic Ice Sheet. 

Today, most of the continent is covered in many interconnected glaciers, which together make up the largest ice sheet on earth. 

Byrd Glacier by NASA on The Commons
Byrd Glacier by NASA on The Commons
piedmont glacier
Antarctic ice flowing over the sea
Speed of Antarctic ice flows LANL simulation
Speed of Antarctic ice flows. Image Source: Los Alamos National Lab, U.S. Department of Energy.
sastrugi
Sastrugi

Does Antarctic land ice move?

Antarctic Ice

Antarctic ice is always in motion. Powered by the force of gravity and its own colossal weight, it oozes like a slow-motion river from the mountains towards the sea. The ice is also shaped by the constant motion of the wind, which carves it into solid, wave-like shapes and whimsical sculptures called sastrugi.

Exactly how fast the ice moves is influenced by many factors including the steepness of the terrain and the material it flows over. In the middle of the ice sheet the ice moves very slowly, just a few feet per year.  In some places, as the ice streams into deep gorges and steep valleys near the coast, it reaches speeds of more than 3000 feet (more than 1 kilometer) per year. The speed of the ice is also influenced by the material it is flowing over. Ice moves relatively slowly over rough, highly textured surfaces like rocks and ridges and speeds up over slippery, soft surfaces like water and sand. 

Video: NASA Goddard’s Scientific Visualization Studio
antarctic map
Image credit: NOAA Climate.gov

Antarctica’s three ice sheets

Antarctic Ice

Antarctica and its ice sheet are often divided into three main sectors: the East Antarctic, West Antarctic, and the much smaller Antarctic Peninsula ice sheet. 

East and west are separated by the Transantarctic Mountains, which rise about 2.5 miles (4km) above sea level and extend more than 2,000 miles (3200km) along the Antarctic continent. 

The Antarctic Peninsula Ice Sheet blankets a narrow, rocky mountain range, which extends out from the main bulk of Antarctica like a finger pointing towards South America. 

Antarctic bedrock topography map
Image credit: NASA Goddard’s Scientific Visualization Studio
bedrock map of Antarctica
Image credit: NASA Goddard Space Flight Center
NASA's bedrock bedmap of Antarctica
Image credti: NASA

East Antarctic Ice Sheet

Antarctic Ice

East Antarctica is the highest, driest, windiest and coldest place on earth. It is also home to the largest ice sheet on the planet.

Flowing down the eastern flanks of the Transantarctic Mountains, the East Antarctic Ice Sheet contains more than 90% of Antarctica’s ice: enough to raise sea levels by around 170 feet (53 meters).

This frozen fortress contains the South Pole, the Amundsen-Scott South Pole Station (the southernmost human settlement on earth), and the deepest ice on the planet – up to 3 miles (4776 meters) deep. 

The highest point in East Antarctica is Dome Argus. Dome Argus is also the coldest place on earth. The lowest point in East Antarctica is the ice-filled Denman Canyon, the deepest known land canyon on earth. It drops to 11,500ft (3.5km) below sea level – over six times lower than the Dead Sea. 

Beneath the ice

If you look at the ice sheet from above it can look quite smooth and flat, like icing on a wedding cake. But the land it covers is far from smooth. If you could lift the ice and look below, you would find the rocky topography of an ancient continent: jagged mountain ranges, deep canyons, broad glacial valleys and even lakes. 

Antarctic ice profile
Image credit: Hannes Grobe Alfred Wegener Institute for Polar and Marine Research

West Antarctic Ice Sheet

Antarctic Ice

Roughly one tenth of Antarctica’s ice is in the west. Flowing down from the Transantarctic Mountains, the West Antarctic Ice Sheet drains into the Bellingshausen, Weddell, Amundsen and Ross seas via a network of glaciers, ice streams and ice shelves. It holds enough ice to raise sea levels by 10 feet (3 meters) if it all melted. 

West Antarctica is home to the tallest peak in Antarctica, Mt Vinson. The southernmost active volcano on earth, Mt Erebus, is also located in the west. It is situated on Ross Island, which is the southernmost island accessible by sea. 

Beneath the ice

Under the ice, much of West Antarctica is a deep basin that plunges inland away from the coast. If you could lift off the ice, drain the ocean and walk inland from the coast, you would find yourself descending a silty slope, ending up thousands of feet below sea level. If the ice melted, most of West Antarctica would be underwater.

Neko harbour antarctic peninsula glacier
Antarctic glacier dwarfs three travellers.
map of Antarctic Peninsula
Image credit: NASA

Antarctic Peninsula Ice Sheet

Antarctic Ice

The Antarctic Peninsula Ice Sheet is the smallest ice sheet in Antarctica. Extending to a latitude of 63°S, roughly 600 miles (1000 kilometers) from South America, it covers the northernmost part of Antarctica. 

The Antarctic Peninsula ice sheet flows steeply into a series of fast-moving glaciers and ice shelves along the narrow, mountainous spine of the Antarctic Peninsula. It terminates in the Bellingshausen Sea to the west, and the Weddell Sea to the east. 

The Antarctic Peninsula represents only 1% of the Antarctic continent, but it receives 10% of the continent’s annual snowfall thanks to its maritime climate. The build-up of this fresh snow is balanced out by widespread snowmelt in the summer. The Peninsula is the only part of Antarctica to experience significant seasonal melting of its ice sheet. 

Often referred to as the polar ‘banana belt’, the Antarctic Peninsula is one of the most rapidly warming areas in the Southern Hemisphere. Its ice sheet is changing rapidly, with nine out of ten glaciers in this region shrinking. 

Why is the ice sheet important?

The Antarctic Ice Sheet plays a critical role in the Earth’s climate.

sastrugi
Reflecting

The bright, white surface of the ice reflects up to 90% of the solar radiation that reaches it, helping to keep the planet cool.

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Transantarctic mountains
Storing

The Antarctic Ice Sheet contains around 70% of the freshwater on the planet. By storing it as ice, it helps to keep sea levels stable.

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tabular berg
Regulating

By influencing the global ratio of ice (which reflects heat) to water (which absorbs heat), Antarctica acts as a global thermostat.

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iceshelf

ANTARCTIC ICE

Land Ice: Ice shelves

When the ice sheet reaches the sea it keeps flowing over the ocean as a floating plate of ice called an ice shelf.

Antarctic ice shelves
Image credit: Paleo Nim

Ice Shelves

Antarctic Ice

There are approximately 300 ice shelves around Antarctica. Together they cover around three quarters of the Antarctic coastline – roughly the same area as the entire Greenland Ice Sheet. 

Ice shelves vary in size. Some of the larger ones are the size of small nations and over a hundred feet thick. The largest ice shelf on earth, the Ross Ice Shelf, is almost as large as France. It terminates in an ice cliff more than 370 miles (600 kilometers) long, towering up to 160 feet (150 meters) above the ocean.

While ice shelves float on the sea, they are not considered sea ice. They are floating extensions of the Antarctic Ice Sheet, and contain freshwater ice that comes from the continent. One important difference between the ice sheet and its floating ice shelves is that ice shelves don’t contribute to sea level rise when they melt. As they are floating, they have already displaced the same amount of water they contain – much like when you put an ice cube in a glass, and the water level goes up. However, ice shelves play an important role in slowing sea level rise by slowing the flow of the ice sheet itself.

Why are ice shelves important?

Ice shelves support Antarctic ecosystems and play a vital role in slowing global sea level rise.

antarctic glacier from above
Stabilizing

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Under ice algae
Ecosystems

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tabular berg
Icebergs

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Pancake Ice

ANTARCTIC ICE

Sea Ice

Each winter, the Antarctic coastline is transformed as the ocean freezes over, surrounding the continent with a fringe of ice as large as the continent itself.

At its winter maximum, Antarctic sea ice covers an area of around 11 million square miles (18 million sq.km): almost twice the size of the United States of America, and larger than Antarctica itself. 

Grease ice
Grease ice
Antarctic seasonal ice change.
Antarctic seasonal ice change. Image credit: NASA Goddard Space Flight Center Scientific Visualization Studio/ NASA Earth Observatory/ Jesse Allen
antarctica from above
View of Antarctic sea ice from above

How does sea ice form? 

Antarctic Ice

Unlike the Antarctic Ice Sheet and ice shelves, which formed over millennia, Antarctic sea ice forms over weeks, days or even hours. When sea temperatures drop below 28.4°F (-1.8°C)* sea water begins to freeze. Small crystals begin to form in the ocean, which gradually accumulate into slush, then ice. 

Exactly how the sea ice forms depends on the state of the sea. In a quiet, sheltered bay, sea ice may form as a surface slick, gradually becoming thicker and deeper. In stormy seas, ice crystals may form in both shallow and deep water, colliding and congealing into plates of sea ice over time. 

Sea ice floating on the ocean is extremely dynamic. It drifts with the tides, currents and wind, and collides with coastlines and icebergs. The surface of sea ice is generally uneven, a landscape of jumbled blocks, mounds of ice many feet high, slushy clumps and ever-changing leads of open water. By contrast landfast sea ice, often referred to as fast ice, is anchored to the coast or the sea floor, and isn’t affected by winds or currents.

Where does sea ice go in the summer?

In contrast to Arctic sea ice, which can remain for many seasons, Antarctic sea ice generally lasts only a year, with the exception of some fast ice. It reaches a typical thickness or around 3 feet (1 meter), but maximum thicknesses of three times that are normal in areas where ice converges due to winds and currents, and gets rafted into ridges. During spring the sea ice begins to melt in the most dramatic seasonal change on earth.

As sea ice melts, millions of microscopic plants and animals sheltering the ice are released into a sun-drenched sea, kickstarting an explosion of life that spreads across the Southern Ocean, animated by nearly 24 hours of sunlight each day. 

*The salt in seawater causes the freezing point to drop below 32°F/0°C.

Why is sea ice important?

Antarctic sea ice has impacts on a global scale.

Satellite image of Antarctica by NASA
Cooling

The white surface of the sea ice reflects much of the sun’s heat back to space, helping to keep the Earth cool.

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Antarctic cushion sea star
Protecting

Sea ice is an important habitat for phytoplankton, microscopic plants which form the foundation of the Antarctic food web.

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water mass bodies of the Southern Ocean
Producing

When sea ice forms it creates Antarctic Bottom Water (AABW), the heaviest, most dense water on the planet.

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KEEP LEARNING

Related reading

iceshelf

Melting ice

Warm ocean currents melt Antarctic ice.

Pancake Ice

Changing ice

Winter sea ice in Antarctica is changing.

Transantarctic mountains

Rising seas

The Antarctic Ice Sheet is in decline.

Antarctic waterfall

Climate crisis

Parts of Antarctica are changing rapidly.

penguin chicks

Life on the ice

Reduced sea ice is impacting Antarctic life.

Photo credit: Erwan AMICE (Diplulmaris antarctica)

Now that you’ve learned about Antarctic ice, read on to learn more about this extraordinary continent.

Antarctic Ice

FEATURED LEARNING

Tabular icebergs and plates of sea ice.
Tabular icebergs and plates of sea ice.
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