Antarctic ice sheet

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Context: Global warming is putting the continent’s ice at risk of destruction in many forms. But one especially calamitous scenario might be a less pressing concern, a new study has found.

Details

What is Ice Sheet?

• An ice sheetis a mass of glacial ice more than 50,000 square kilometers (19,000 square miles). Ice sheets contain about 99% of the fresh water on Earth, and are sometimes called continental glaciers.

Ice Shelves:

• As ice sheets extend to the coast and over the ocean, they become ice shelves.

Ice Cap:

• A mass of glacial ice covering less area than an ice sheet is called an ice cap.

Ice Field and Glacier:

• A series of connected ice caps is called an ice field. Making up ice fields, ice caps, and eventually ice sheets are individual glaciers.

Examples

• There are only two ice sheets in the world: the Antarctic ice sheet and the Greenland ice sheet.

Formation of Ice Sheets

• Two type: Land Ice (also known as meteoric ice) and Sea Ice

Land Ice Formation

• Snow accumulatesyear after year, then melts.
• The slightly melted snow gets harder and compresses.
• It slowly changes texture from fluffy powder to a block of hard, round ice pellets.
• New snow falls and buries the grainy snow.
• The hard snow underneath gets even denser. It is known as firn. As years go by, layers of firn build on top of each other.
• When the ice grows thick enough (about 50 meters) the firn grains fuseinto a huge mass of solid ice.

Characteristic

• Ice sheets tend to be slightly dome-shaped and spread out from their center.
• They behave plastically, or like a liquid.

Movement

• When the ice grows thick enough, the glacier begins to move under its own weight.
• Compression and geothermal energysometimes cause the bottom of an ice sheet to be slightly warmer than the ice above it.
• The bottom of the ice sheet melts, causing the ice above it to move at a faster rate than the rest of the ice sheet. These fast-moving glaciers are called ice streams.
• An ice sheet flows, oozes, and slides over uneven surfaces until it covers everything in its path, including entire valleys, mountains, and plains.
• Ice streams can move as quickly as 1,000 meters (0.6 mile) every year.

Ice streams

• The largest glacier in the world is an ice stream, the Lambert Glacier in Antarctica.
• The Lambert Glacier moves as quickly as 1,200 meters (0.7 mile) every year.
• It is more than 400 kilometers (249 miles) long and 2,500 meters (1.5 miles) thick.

Sea 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.

Why are ice sheets important?

• Ice sheets contain enormous quantities of frozen water.
• If the Greenland Ice Sheet melted entirely, scientists estimate that sea level would rise about 4 meters (23 feet).
• If the Antarctic Ice Sheet melted, sea level would rise by about 58 meters (190 feet).
• The Greenland and Antarctic Ice Sheets also influence weather and climate.
• Large high-altitude plateaus on the ice sheets alter storm tracks and create cold downslope winds close to the ice surface.
• Known as katabatic winds, these downslope winds occur when the higher altitudes radiate heat and are cooled. As the air cools, it becomes denser. Gravity does the rest by pulling this denser air downhill.
• Along with influencing the ocean and atmosphere, ice sheets are important because they contain annual layers that hold a unique and valuable record of Earth's climate history.
• Pockets of air bubbles locked within the ice can tell scientists what our planet’s climate was like nearly one million years ago.

Ice sheets and wildlife

• Though algae lives on ice, ice sheets host few animals.
• Flora and fauna in Greenland and Antarctica is present primarily at and beyond the ice sheet edges.
• In Greenland, large mammals like polar bears, seals, and walruses, navigate between the sea ice and shores. On land, musk oxen, caribou, and the white Arctic fox are some of the larger roaming animals. The waters surrounding Greenland are also home to humpback whales and narwhals.
• About 60 species of birds call Greenland home, with another 20 as regular migrants. Among the most striking species is the white-tailed eagle, or nattoralik in Greenlandic.
• Between 17 and 19 penguin species exist (depending on how they are categorized), nine of which live in Antarctica and its surrounding islands.

The Antarctic Ice Sheet

• The Antarctic ice sheet is the largest block of ice on Earth.
• It covers more than 14 million square kilometers (5.4 million square miles) and contains about 30 million cubic kilometers (7.2 million cubic miles) of water.
• The Antarctic ice sheet is about two kilometers (1.2 miles) thick.
• Formation: It started to form between 34 and 35 million years ago.

Antarctica’s three ice sheets

• 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 pointing towards South America. 

East Antarctic Ice Sheet

• 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.

West Antarctic Ice Sheet

• 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.

Antarctic Peninsula Ice Sheet

• 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 due to its maritime climate.
• 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. 

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

Reflecting

• As the largest ice mass on the planet, the Antarctic Ice Sheet plays a vital role in the overall energy balance of the earth. 
• The bright, white surface of the ice reflects up to 90% of the solar radiation that reaches it, helping to keep the planet cool. 
• Ice has a higher ‘albedo’ (reflective capacity) than the ocean and land surfaces. 

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.
• By locking up all this water, the ice sheet plays an important role in setting sea levels around the planet. For over 10,000 years, sea levels have been relatively stable.
• During a warm period around 400,000 years ago, sea levels rose by over 20 feet (6 meters) due to melting Antarctic ice.

Regulating

• Antarctic ice, in combination with the cold, dry atmosphere above it and the Southern Ocean that surrounds it, acts as a powerful global thermostat.

Antarctica Ice Shelves

• There are approximately 300 ice shelves around Antarctica.
• The largest ice shelf on earth, the Ross Ice Shelf. It terminates in an ice cliff more than 370 miles (600 kilometers) long, towering up to 160 feet (150 meters) above the ocean.

Significance

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

Stabilizing

• Ice shelves act as a brake for the Antarctic Ice Sheet. When they collapse, the ice sheet begins to flow more quickly, leading to sea level rise.
• Collapsing ice shelves don’t contribute directly to rising sea levels because they are already floating on the ocean, but they do offer a critical line of defense.
• Ice shelves act as a brake for the glaciers that make up the Antarctic Ice Sheet.
• When ice shelves melt the glaciers behind them soon follow, contributing directly to sea level rise.
• Ice shelves slow the flow of the ice sheet by pushing back against the glaciers that feed them, helping to slow their flow by acting as a buttress, or a braking system for the ice. 

Ecosystems

• Beneath the ice shelves is a unique habitat where unusual and highly specialized fish, crustaceans and invertebrates thrive. 
• Beneath the Ross Ice Shelf under nearly 2,500 feet (740 meters) of ice, communities of fish, jellyfish and amphipods (a kind of crustacean) thrive in extremely cold, dark waters.
• An array of life including brittle stars, soft corals and anemones has also been found under the McMurdo Ice Shelf, 50 miles (80km) from open water.  

Icebergs

• Tabular icebergs calve off the front of ice shelves.

Eg: Aa23 iceburg.

Melting Ice Sheets

• Glaciers melt when ice melts more quickly than firn can accumulate. Because they are so large, melting ice sheets can affect the climate of ecosystems in the entire world.

Climate Change and effects on Antarctica

• It is one of the fastest warming parts of the world.
• Antarctica is losing a staggering 150 billion tons of glacier ice a year, and this rate of ice loss is accelerating.
• The main cause is ocean warming, which not only melts the ice sheet directly, but also thins the floating ice shelves that hold the ice sheet on land.
• As the ice shelves lose strength, they allow more ice to flow into the sea, raising the sea level.
• The sea ice that surrounds the continent has been shrinking since 2016.
• The air above Antarctica is also heating up, causing surface melting that can trigger the collapse of ice shelves.
• In March 2022, East Antarctica was hit by the most extreme heatwave ever recorded on Earth, with temperatures soaring 38℃ above normal.
• The West Antarctic Ice Sheet, which could raise global sea level by over three metres, depends on the Thwaites Glacier’s stability. This part of the ice sheet rests on a downward-sloping submarine bed, making it prone to irreversible retreat.

Consequences  

Sea level rise and Coastal Cities:

• A melting ice sheet could have on some coastal U.S. cities, such as New York City, New York; Washington. These cities could become underwater cities if ice sheets melt enough to raise the sea level significantly.

Salinity:

• Melting ice sheets also reduce the ocean’s salinity, or salt content. Tons of freshwater are added to the ocean every day by melting ice sheets.
• Large additions of freshwater change the ocean ecosystems. Organisms, such as many types of corals, depend on saltwater for survival. Some corals may not be able to adjust to a more freshwater habitat.

Thermohaline circulation:

• Also called "ocean conveyor belt," would be radically altered by melting ice sheets.
• The ocean conveyor belt circulates nutrient-rich water from polar regions throughout the world's oceans in a long, slow, continual loop.
• Circulation relies on the relationship between water with different densities. Cold, saline water from polar regions gradually rises to the surface in the tropics.

Polar marine ecosystem:

• Melting ice sheets would increase the amount of warm and fresh water in polar marine ecosystems. This would slow "deep water formation," the development of cold, saline, nutrient-rich water on which entire marine ecosystems depend.
• According to the United Nations, sea ice may decrease by 25% within the next century. This may lead to a reduction in krill, the basis of the Antarctic marine food web.
• Animals from crustaceans to penguins will face much greater competition for fewer food resources.

Coastal habitats:  

• Coastal habitats are put at risk of being flooded. In March 2008, a 400-square kilometer (160-square-mile) piece of the Wilkins Ice Shelf broke off of the Antarctic Peninsula.
• A 2020 study found that global mean sea level rise of one metre by 2100 would cause annual flood damages to increase by two to three orders of magnitude, affecting up to 3% of global GDP.

Shipping:

• Large icebergs created by such an event create hazards for shipping.

The solutions

Cutting greenhouse gas emissions:

• Some sea level rise from Antarctica is now inevitable, but can still avoid the worst impacts by urgently cutting greenhouse gas emissions.

Sharm El-Sheikh Implementation plan:

• The Sharm El-Sheikh Implementation plan, adopted at COP27, recognized the impacts of climate change on the cryosphere.

COP 28

• Negotiations at COP28 need to build on this momentum and recognize that limiting global warming to 1.5C is a physical necessity to prevent the irreversible collapse of West Antarctica.

Renewable energy

• Renewable energy is growing exponentially and is projected to provide over one-third of global electricity by 2030 and overtake fossil fuels.

Societal change:

• These are rapid shifts in human behaviour, technology, policy or markets that can lead to large-scale transformations that reduce emissions and enhance resilience.

More Details

West Antarctica:  https://www.iasgyan.in/daily-current-affairs/west-antarctica#:~:text=The%20highest%20point%20of%20antarctica,younger%2C%20volcanic%20and%20sedimentary%20rock.

Record-Breaking Heatwave in Antarctica : https://www.iasgyan.in/daily-current-affairs/record-breaking-heatwave-in-antarctica

A23a glacier: https://www.iasgyan.in/daily-current-affairs/a23a#:~:text=Iceberg%20A23a%20calved%20from%20the,Part%20of%20Antarctic%20ice%20sheet).&text=Its%20current%20title%20as%20the,since%20broken%20into%20three%20pieces.

https://www.iasgyan.in/daily-current-affairs/a23a-iceberg

Geological link between India and Antartica: https://www.iasgyan.in/daily-current-affairs/geological-link-between-india-and-antartica

Source

https://www.asoc.org/learn/antarctic-ice/

https://indianexpress.com/article/explained/explained-climate/antarcticas-ice-sheet-break-away-9527198/

https://www.weforum.org/agenda/2023/03/antarctic-ice-sheet-is-melting-humanity-climate/

https://education.nationalgeographic.org/resource/ice-sheet/