The Antarctic Circle & Marguerite Bay

The Line on the Map

What the Antarctic Circle really means

The Antarctic Circle is the line of latitude at roughly 66 degrees 33 minutes south. South of it, the sun stays above the horizon for at least one full day around the December solstice, and stays below it for at least one full day in June. Because the Earth's axis wobbles very slightly over thousands of years, the line is not perfectly fixed and creeps a few metres a year, but 66°33′ is the figure on every chart and the one the ship's officers will be watching.

Only a small proportion of visitors to Antarctica ever cross it. Most cruises stay further north, where the bays are more sheltered and the ice less of a gamble. The Antarctic Circle sits a long way down the west coast of the Peninsula, beyond the Lemaire Channel and the Argentine Islands, and reaching it means sailing through waters that are often choked with pack ice well into the summer. When a ship does get through, the reward is a quieter, colder, more remote Antarctica, with the long light of the midnight sun spilling across the ice.

Around the December solstice the sun does not set at all at the circle. You can stand on deck at midnight with the light low and golden, and a few hours later it is climbing again. Even in January and early February the nights are short, which makes the most of every hour you are there.

An Expedition Tradition

Crossing the Antarctic Circle

Sailors have always marked big crossings, and the Antarctic Circle is no exception. When the ship reaches 66°33′ the Bridge will usually sound the horn and make an announcement, and guests gather out on deck. Expect a little ceremony: on many expedition voyages there is a toast, sometimes a playful visit from King Neptune or a bucket of icy water for anyone brave enough, and a certificate to take home as proof. The details vary from ship to ship and voyage to voyage, and the Expedition Team like to keep a few surprises up their sleeves.

It matters most, though, because of what it represents. Crossing the circle is never guaranteed, which is why HX describe their Antarctic Circle Expedition as an Attempt voyage. The ice south of the Lemaire Channel can close in at any time, and the Captain will only press on if it is safe. If the ship cannot get through, the itinerary is adapted and the time is spent exploring elsewhere on the Peninsula.

South of the Lemaire

Places to visit around Marguerite Bay

Marguerite Bay is a broad bay on the west coast of the Peninsula, just south of the Antarctic Circle, bounded to the north by Adelaide Island. It was charted by the French explorer Jean-Baptiste Charcot in 1909 and named after his wife. Its fjords and islands hold some of the best preserved huts of the British research era, and some of the most southerly wildlife colonies that expedition ships can reach.

The Fish Islands

Just north of the circle, at the entrance to Holtedahl Bay, the Fish Islands are a cluster of small rocky islets with around 4,000 pairs of Adélie penguins and a small colony of blue eyed shags. They make an excellent stop on the way south, with small boat cruising among the islets and the chance of a landing if the ice allows.

Detaille Island

Detaille Island, in Crystal Sound just south of the circle, was the site of British Base W, built in 1956 for surveying and geology. In March 1959 the sea ice failed to clear and the relief ship could not get in, so the men had to leave in a hurry, crossing the sea ice to reach the ship. The hut has stood almost untouched ever since, with tins on the shelves, clothes on the pegs and notes on the table. It is now a Historic Site and Monument, cared for by the UK Antarctic Heritage Trust, and stepping inside is like opening a time capsule.

Horseshoe Island

Further south in Marguerite Bay, Horseshoe Island was home to British Base Y from 1955 to 1960. The station is one of the most complete examples of a British base from that era, with its generator shed, radio room, bunk room and workshop all still fitted out. A walk up behind the hut gives views over the mountains and glaciers of the bay. Like Detaille, it is a protected Historic Site and Monument looked after by the UK Antarctic Heritage Trust.

Stonington Island

Tiny Stonington Island, once linked to the mainland by a glacier, has two bases side by side. East Base was built by the United States Antarctic Service Expedition in 1940 and used again by the Ronne Antarctic Research Expedition of 1947 to 1948, when Edith Ronne and Jennie Darlington became the first women to spend a winter in Antarctica. Britain's Base E operated alongside it from 1946 to 1975, and was a centre for dog sledging and survey work deep into the interior. Both are protected historic sites.

Adelaide Island

Adelaide Island, discovered by John Biscoe in 1832 and named after Queen Adelaide, forms the northern edge of Marguerite Bay. It is a long, mountainous island almost entirely covered by ice, and the British Antarctic Survey's main research station, Rothera, stands on its southeastern tip. Visits to the station are rare, but the scenery as you sail along the island's coast is magnificent.

What You Will See

Wildlife south of the circle

The further south you go on the Peninsula, the more Adélie penguins take over from gentoos. Adélies are true ice penguins, small, feisty and endlessly entertaining, and the colonies around Marguerite Bay are among the most southerly that expedition ships can reach. By January the chicks are hatching and both parents are busy shuttling back and forth with krill, so there is constant traffic between the colony and the sea.

The pack ice here is good for seals. Crabeater seals lie in groups on the floes, Weddell seals rest on the fast ice close to shore, and leopard seals wait near the penguin colonies. Humpback and minke whales feed in the open water, and orcas hunt along the ice edges. This is also the best part of the Peninsula for snow petrels, pure white and usually seen near the pack. You can read more in our Antarctic wildlife guide.

Timing

When to cross the Antarctic Circle

The window is short. Before Christmas the sea ice south of the Lemaire Channel is often too thick, and by March the weather is turning. That is why crossing voyages, such as HX's Antarctic Circle Expedition, are scheduled between late December and February, when the sea ice has broken up as much as it will, the days are longest and Adélie chicks are in the colonies. Even then, each year is different. For a broader picture of the season, see our when to go guide.

Voyages That Visit

Cruises across the Antarctic Circle

HX Expeditions

The Antarctic Circle Expedition on MS Roald Amundsen is the one HX voyage in the 2026/27 programme planned around a crossing. It sails from Ushuaia on 26 December 2026 and 9 January, 23 January and 6 February 2027, with flights between Buenos Aires and Ushuaia included. Other voyages with plenty of days in Antarctica, such as Iconic Antarctica, The Explorer's Route, head south towards the Penola Strait but do not plan to reach the circle.

See how it compares on our Antarctica cruises page, read about the ship on our MS Roald Amundsen page, or explore the rest of the Antarctic Peninsula.