Icebergs<\/h2>\n\n\n\n
Icebergs are the heralds of Antarctica: when sailing across the Drake Passage from South America, it\u2019s always a thrill when the first iceberg of the trip looms into view on the horizon (we\u2019ve even been expedition cruise ships that run a sweepstake to guess the hour of the first sighting). <\/p>\n\n\n\n Icebergs are enormous chunks of ice that have broken off a glacier or ice shelf. The biggest icebergs can be unfathomably huge: in 2025, satellites tracked A23a, the largest iceberg in the world, as it drifted from the Weddell Sea to eventually ground itself close to South Georgia. It measured around 3,500 square kilometres (1,400 sq mi) – more than twice the size of London. Since 90% of an iceberg sits under the water, the dimensions under the surface were almost as staggering: with cliffs reaching 40 metres high, A23A hid almost 360 metres of ice below the waves. <\/p>\n\n\n\n Most icebergs encountered on an Antarctic cruise are far smaller, of course. As a rule, anything 5 metres above the surface is classified as an iceberg. Smaller than this \u2014 down to around a metre \u2014 and the ice is charmingly referred to as a bergy bit. <\/p>\n\n\n\n Less charming are the growlers, which is what you get when there\u2019s just a metre of ice showing above the water. These are generally too small to be picked up by a ship\u2019s radar, but still chunky enough to cause potential hazards. They\u2019re one reason why expedition cruise ships are equipped with the most advanced navigation equipment and have the best navigators in the business on the bridge when sailing in polar waters.\u00a0<\/p>\n\n\n\n As icebergs were born from glaciers, the products of ancient snowfall, they\u2019re made of freshwater. When Captain Cook led the first recorded crossing of the Antarctic Circle<\/a> in 1773, his ships were able to sustain themselves with water by fishing broken chunks of icebergs from the sea. But not all of Antarctica\u2019s ice makes good drinking water: most of it is salty. <\/p>\n\n\n\n Every year, Antarctica undergoes the greatest environmental change on the planet. When the sun disappears for the winter, the sea around Antarctica freezes, effectively doubling the size of the continent. This sea ice \u2014 usually just a couple of metres thick \u2014 is of enormous importance to the Southern Ocean and our planet\u2019s climate. <\/p>\n\n\n\n By limiting the amount of sunlight that reaches the sea, sea ice regulates the growth of phytoplankton, which is the basis of all life in the ocean, as well as providing a nursery for that essential ecosystem inhabitant, Antarctic krill<\/a>. Where the sea absorbs the sun\u2019s heat, sea ice reflects it back, and then helps keep the ocean and atmosphere cool as it melts every season. In recent years, there has been a big decrease<\/a> in the extent of Antarctic sea ice, for reasons that scientists are still trying to unravel.<\/p>\n\n\n\n If you travel to the Antarctic Peninsula<\/a> in the spring and early summer, you\u2019ll experience the last of the sea ice on the Antarctic Peninsula, which by this time has largely melted into brash ice \u2013 loose accumulations of small sea ice. Taking a zodiac cruise through brash ice<\/a> is a real treat, hearing the ice brush against its hull and seeing it gently ripple like a carpet around you. Any larger surviving large chunks are called rotten ice, which are honeycombed with meltwater and not long for the world. <\/p>\n\n\n\n Mixed in with the brash ice will undoubtedly be plenty of bergy bits, growlers and small pieces of freshwater glacial ice. These can be extraordinary shades of blue \u2013 and the bluer the colour the older the ice. Over thousands of years, air is slowly squeezed out of the glacier ice, changing the way it refracts light, hence its colour. Pluck a piece of glacier ice from the water and hold it to your ears and you can listen to it melt with tiny pops and pings as thousand-year-old air escapes into the atmosphere. The clearest and glassiest chunks are often collected as trophies for the ship\u2019s bar: since they would naturally melt anyway, why not take a piece to cool a cocktail in the evening?<\/p>\n\n\n\n By contrast, if you\u2019re in the Peninsula at the very end of the season<\/a>, you may get to witness the magic of sea ice forming in front of your very eyes. As the sea cools, the first phase is the formation of frazil ice, tiny specks of ice that begin to form a loose slush on the surface. This coagulates into thin layers called grease ice, and as it thickens, it becomes pancake ice. This looks as the name suggests, and is as thick as your hand and up to three metres across. As the sea continues to freeze, large floes form, eventually joining together into massive sheets, or forming a giant mosaic of pack ice. <\/p>\n\n\n\n Most sea ice is born and disappears in a single year, but in some parts of Antarctica, such as the Weddell Sea<\/a>, it can persist over several years. This old ice becomes increasingly thick, and requires an icebreaker to penetrate. It was the thick pack ice of the Weddell Sea that caught Shackleton\u2019s ship Endurance<\/a> in 1915, crushing his hopes of crossing Antarctica. <\/p>\n\n\n\n When the first explorers started to probe Antarctica at the end of the 19th Century, it was unclear whether it was a new continent or a collection of islands. The reason for this uncertainty was the enormous ice sheet that covers everything. <\/p>\n\n\n\n As with everything Antarctic, the statistics are hard to comprehend. The Antarctic Ice Sheet is nearly 14 million square kilometres (5.4 million square miles), and holds about 60% of all the fresh water on the planet in its giant mass. If that was to melt, it would cause global sea levels to rise by 70 metres. <\/p>\n\n\n\n There are two ice sheets, either side of the Transantarctic Mountains<\/a> that run the length of the continent. The East Antarctic Ice Sheet lies on the land mass of the continent, but much of the West Antarctic Ice Sheet (in the half of the continent that includes the Weddell Sea and the Peninsula) is so thick that its bottom sits 2,500 metres (8,200 feet) below sea level, on what was be the sea bed if it wasn\u2019t frozen. <\/p>\n\n\n\n The ice sheet forms a white reflective dome over Antarctica, helping keep the continent cold. Snow falling on the ice sheet never melts, even in summer, but builds up over the years, centuries and even millennia, eventually transforming into thick glacier ice.\u00a0<\/p>\n\n\n\n Even in summer Antarctic temperatures are below 0\u00b0C and so frost and snow crystals that gather on the surface of the ice sheet do not melt, but accumulate year-by-year. As these crystals are buried, the weight of the ice above presses them together. Eventually, they are transformed into dense and impermeable glacial ice. The oldest ice surveyed on the East Antarctic ice sheet is one million years old<\/a>, which scientists are using to better understand our ancient climate and what it can tell us about our changing world today. <\/p>\n\n\n\n Where Antarctica\u2019s ice sheets meet the ocean at the continental edge, you find ice shelves. These are immense sheets of ice that, instead of sitting on bed rock, find themselves floating in water. More than 75% of Antarctica\u2019s coastline is surrounded by ice shelves. <\/p>\n\n\n\n Although Antarctica is fringed with ice shelves, two are particularly famous. The first is the Ross Ice Shelf on the edge of the Ross Sea<\/a>, encountered by explorers like Shackleton, Amundsen, Scott and James Clark Ross. Ross gave his name to both the sea and the ice shelf, which he knew simply as \u2018The Barrier\u2019 due to its impenetrable nature. The Ross Ice Shelf is slightly larger than France. <\/p>\n\n\n\n In West Antarctica, the Filchner\u2013Ronne Ice Shelf protrudes into the Weddell Sea. The A23a iceberg was calved from this shelf back in 1986, and spent nearly 40 years grounded on the sea bed before floating free into the open ocean. Seeing the immense tabular icebergs<\/a> that are born here from the Filchner\u2013Ronne Ice Shelf is one of the most magical parts of a visit to the Weddell Sea. <\/p>\n\n\n\n![\"\"](\"https:\/\/www.swoop-antarctica.com\/blog\/wp-content\/uploads\/2025\/09\/53567032066_0461fbfd07_6k-1024x576.jpg\")
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Sea ice<\/h2>\n\n\n\n
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New ice and old ice<\/h2>\n\n\n\n
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Ice sheets<\/h2>\n\n\n\n
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<\/figcaption><\/figure>\n\n\n\nIce shelves<\/h2>\n\n\n\n
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