Antarctica holds the largest single mass of ice on Earth, covering around 14 million square kilometres. The ice sheet that blankets the continent has an average thickness of approximately 2.2 kilometres (1.3 miles), with some areas—particularly in East Antarctica—reaching depths of over 4.7 kilometres (nearly 3 miles). This vast ice sheet contains about 90% of the world’s freshwater ice and plays a crucial role in regulating global sea levels and the Earth’s climate system.
The immense thickness of Antarctica’s ice has a significant impact on the continent’s landscape. In many regions, the weight of the ice is so great that it depresses the land beneath it, pushing parts of the bedrock below sea level. Scientists closely monitor the thickness and movement of Antarctic ice to better understand how it might respond to climate change. If the entire Antarctic ice sheet were to melt, it could lead to a global sea level rise of around 58 metres (190 feet), dramatically altering coastlines and low-lying regions across the world.
A glacier is any mass of ice and permanent snow with an area greater than 0.01 km², formed on Earth by the successive accumulation of layers of snow. A glacier must remain observable at the end of the melting season for at least two years and must have well-defined boundaries. The definition of a glacier includes all feeders and connected tributaries that contribute ice to the main glacier.
Glaciers flow either into ice shelves (which float on the sea) or directly into the ocean, where portions break off and form floating masses called icebergs. Carried by circumpolar currents and prevailing winds, these icebergs drift westward around the continent and then northward to the Antarctic Convergence, before gradually breaking up and melting upon contact with warmer waters.
The average lifespan of Antarctic ice in the continent's interior—from the falling of snow to the calving of icebergs—is about 700,000 years.
Icebergs move primarily due to a combination of ocean currents, wind, and tides. Ocean currents are the main force behind the movement of icebergs. These currents are driven by wind, water temperature, salinity differences, and the Earth's rotation (Coriolis effect). Icebergs are also influenced by surface currents, which can transport them over long distances. For example, icebergs from Greenland often travel south along the Labrador Current.
The Coriolis effect, caused by the Earth's rotation, makes moving icebergs drift to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This effect slightly alters their paths over long distances.
Tidal forces cause periodic changes in water levels and currents, which can influence the movement of icebergs. Tidal currents can push icebergs in different directions depending on the tide phase (incoming or outgoing).
Wind can also have a significant impact on the drift of icebergs, pushing them in the direction of the wind and often affecting their speed and trajectory. The effect of wind is more pronounced on smaller icebergs and those with a higher surface area above the water.
Gravity affects an iceberg’s balance and buoyancy, ensuring that approximately 80–90% of its mass is submerged underwater. The submerged part interacts more with ocean currents, determining the iceberg’s overall direction and speed.
As icebergs drift into warmer waters, they melt and break apart. This can change their shape, size, and buoyancy, altering how they interact with currents and wind.
The interplay of all these factors leads to the dynamic and often unpredictable movement of icebergs in the ocean.
Icebergs are named based on the quadrant of Antarctica from which they originated:
- A: 0° to 90°W (Bellingshausen and Weddell Sea)
- B: 90°W to 180°W (Amundsen Sea and eastern Ross Sea)
- C: 180° to 90°E (western Ross Sea and Wilkes Land)
- D: 90°E to 0° (Lazarev Sea and Davis Sea)
When first sighted, an iceberg’s point of origin is documented by the U.S. National Ice Center (USNIC). The iceberg is assigned a letter corresponding to its quadrant, along with a sequential number. For example, C-19 is the 19th iceberg tracked by USNIC in Quadrant C (between 180° and 90°E).
Icebergs with letter suffixes have calved from already named icebergs. These suffixes are added in sequential order (e.g., C-19A, C-19B, etc.).
Ice analysts use a combination of Synthetic Aperture Radar (SAR), visible light, and infrared remotely sensed imagery to locate and track icebergs in Antarctica. Since 1978, USNIC has been compiling the latitude, longitude, and general size of icebergs observed during routine monitoring of sea ice conditions around the Antarctic continent and has made this data publicly available.
The U.S. National Ice Center (USNIC) is the global entity responsible for naming, tracking, and documenting Antarctic icebergs that meet the criteria of being at least 20 square nautical miles in area or 10 nautical miles along their longest axis. These large icebergs can be tracked online at the official USNIC website: www.usicecenter.gov.
Freshwater Ice
Ice Shelf
A large slab of ice that extends from land and floats on the sea while remaining attached to and partly fed by land-based ice.
Glacier
A mass of ice, regardless of size, formed from compacted snow. It continuously moves from higher to lower ground or spreads outward into the sea.
Iceberg
A large piece of ice—typically tens of meters across or more—that has broken off (calved) from a glacier into a lake or the sea.
Types of Icebergs
Grounded Berg
An iceberg that has run aground in shallow coastal waters and is unable to drift.
Tabular Berg
A flat-topped iceberg, usually calved from an ice shelf. These icebergs can drift for years before melting.
Rolled Berg
An iceberg that has flipped over due to uneven melting, usually from below, which makes it top-heavy. These often have a smooth, rounded appearance.
Calving
The process by which chunks of ice break off from the edge of a glacier into water.
Bergy Bit
A medium-sized piece of floating glacier ice, several meters across, typically resulting from the breakup of an iceberg.
Growler
A smaller piece of glacier ice, almost completely submerged. It is a few meters across but smaller than a bergy bit.
Brash Ice
Small fragments of glacier ice, smaller than growlers, typically resulting from the disintegration of larger ice pieces.
Seawater Ice
Sea Ice
Ice formed by the freezing of seawater. Seawater typically freezes at around -1.8°C (28.8°F), depending on salinity (more salt = lower freezing point).
Antarctic Sea Ice Extent
Ranges from approximately 4 million km² in summer to up to 19 million km² in winter.
Types and Features of Sea Ice
Grease Ice
The first stage of sea ice formation, where small ice crystals cluster into a slick, greasy-looking surface.
Pancake Ice
Circular disks of ice (up to 3 meters in diameter) that form when grease ice thickens and is shaped by wave action.
Pack Ice
Ice floes that have frozen together into larger, consolidated areas.
Polynya
An area of open water surrounded by sea ice, typically caused by wind or current patterns that prevent freezing.
Fast Ice
Sea ice that is attached to the coastline or sea floor and remains stationary, unaffected by ocean currents.
Tide Crack
A crack in fast ice caused by the vertical movement of ocean tides beneath the ice.
The color of light we see, for example in the sky, is due to the phenomenon of scattering, or Rayleigh scattering. White light contains all wavelengths; red has the longest wavelength, and blue light has a wavelength about half that of red light. As white light passes through our atmosphere, it bumps into air molecules (mostly oxygen and nitrogen) and is scattered. The shorter the wavelength of the color, the more that color gets scattered by the atmosphere.
Scattering depends on the relative size of the molecule, the light wave, and the number of molecules. When light bumps into particles smaller than the wavelength of the light, it is scattered. The more molecules there are, the more scattering occurs. The size of the molecules in our atmosphere causes blue light to be scattered the most, so when we look up, we see blue everywhere.
However, violet has the shortest visible wavelength and is actually scattered more than blue, but human eyes are much more sensitive to seeing blue light—otherwise, we would perceive the sky as violet, believe it or not.
In ice, scattering also results from molecules and depends on both their size and number. There are far more water molecules in a cubic centimeter of ice than in air, so ice scatters more light per volume than air. That is why a small iceberg can scatter as much light as a large area of the atmosphere.
The reason icebergs can be so blue is that the pressure deep within them is so great that all the air bubbles have collapsed. Or, if air bubbles are present, they are so small that they are smaller than the wavelength of light. So, when we look at them, we see even more blue than we see when looking at the sky.
(Think about ice cubes in your freezer. They look white because the air bubbles are large compared to the wavelength of the light, and big bubbles scatter all wavelengths equally.)
