Visitors to the North Pole in the past 15 months might have happened upon a peculiar sight: a ship, high and dry on the ice pack, her masts upright against the flaming aurora borealis, her bow pointing over the ice sheet, as if sailing on a sea of snow. They might have thought it a polar mirage.

In fact the double-masted schooner, the Tara, with a crew of increasingly smelly scientists and engineers, has been traversing the ice-cap, partly in a recreation of an historic voyage, partly on a scientific expedition and partly on an old-fashioned adventure.

The Tara has travelled farther north than any ship before her, to 88º 32'N, 100 miles (160km) shy of the pole, trapped in an ice floe. This week, 15 months and a few thousand miles after she was first wedged north of Russia, she was approaching the far side of the Arctic ice sheet, about to be spat out into the Fram Strait between Greenland and Svalbard.

The precedent for this journey was set 111 years ago by the Norwegian explorer Fridtjof Nansen. In southwest Greenland he chanced upon the remains of a ship, frozen in an ice floe. He identified it as a vessel that had disappeared three years earlier off the coast of New Siberia and explained its relocation by formulating the theory of transpolar drift, an ice-circulation theory he set out to prove in 1893 on board the Fram, a ship with a specially thickened hull.

Speaking to The Times by satellite phone, Grant Redvers, the chief of the Tara expedition, said: “We talk a lot about Nansen, we are always making comparisons.” The Fram took three years to drift across the Arctic; the Tara was expected to take two years, but the conveyor belt of the Arctic appears to have been accelerated – the expedition is almost over barely a year after it began. At the same time the ice pack that the Tara is crossing has shrunk drastically. The point at which it was first wedged into the ice in September 2006 was more than 280 miles south of the ice edge in September this year. It now seems possible that the Arctic ice pack could disappear entirely within the next 15 years.

Mr Redvers, from Wellington, New Zealand, first became aware of the Tara when it was owned by his compatriot, the yachtsman Sir Peter Blake. It had been built with a thick, round, aluminium hull, designed to rise up when caught between plates of ice like an olive stone crushed between a finger and thumb. Sir Peter was murdered by pirates while on board the ship on the Amazon in 2001, after which it was bought by Etienne Bourgois, head of the French fashion company Agnès B, and deployed to the Arctic last year with funding from the EU and eight crew, with Mr Redvers acting as chief of the expedition.

Days after she first rose above theW ice, a storm blew up and huge waves rolled beneath the ice sheet. “It shattered like a mirror,” said Mr Redvers. The Tara was back in the ocean and the scientific equipment they had unloaded was drifting away on islands of ice. They were able to retrieve it.

There was another scare that winter with a “pressure ridge” caused by colliding plates of ice advancing towards the boat. “It was like a frozen wave, moving in super-slow motion – about a centimetre a second,” said Mr Redvers. “At one stage we attacked it with picks and chainsaws, but there was no way we could stop it.” It leant over the boat, then suddenly it stopped by itself and “we were released from the pinch”, said Mr Redvers.

There have been regular encounters with polar bears: Zagrey, one of two Laika Yakout dogs who guard the ship, narrowly survived a swiping paw. The dogs gave the first warning last week that the Tarawas about to be released from the ice. “They both came back on board,” says Mr Redvers. “Normally it’s really hard to persuade them to get back on the ship. An hour or so later the ice fractured around us.”

Leaving the ice will be one of the most perilous moments of the voyage: the ship could be capsized by colliding fragments of ice floe. “We’re prepared to leave the ship if we have to,” Mr Redvers said.

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