By Jonathan Fildes

Science and technology reporter, BBC News



The boat is now in free water after more than 500 days

Enlarge Image



Tara sailed into the pack-ice in September 2006 and has been allowed to drift with the ocean currents and wind.

The two-masted manned vessel is crammed full of sensors to monitor the ocean, atmosphere and ice.

The ice-strengthened boat is now making its way to the island of Spitsbergen in the Arctic Ocean.

"We are heading north in open water," wrote crew member Vincent Hilaire in the ship's log, which is published online. "The battle with the ice... is over."

Slow progress

Tara is a privately owned polar schooner that was loaned to the European research community for the duration of the expedition.

It is a key part of Damocles (Developing Arctic Modelling and Observing Capabilities for Long-term Environmental Studies), a European-led effort to gather new information on the changing Arctic.

TARA ARCTIC DRIFT EXPEDITION The 36m, 130-tonne boat was in the ice for 504 days The schooner provides habitation for about 10 people Scientists deployed and monitored a number of instruments Experiments study air, ice and ocean behaviour

Last year, Tara measurements revealed the dramatic springtime collapse of surface ozone in the Arctic for the first time.

Over the last 15 months, the boat has covered 5,200km (3,200 miles), including crossing the Noth Pole, drifting at an average speed of 10km per day (6 miles per day).

The boat and its crew celebrated their 500th day stuck in the pack ice on the 17 January 2008.

It was finally set free four days later.

"Toward noon, the ice-edge revealed little by little its face," wrote Mr Hilaire.

"The ice blocks were apparently at the end of their race, some changing into unusual sculptures in their slow but inescapable death."

Open water

The boat was implanted into the ice to act as a floating scientific platform.

Increasingly, polar researchers are finding it difficult to establish semi-permanent camps on the sea ice.

"When you are on a boat at least you are floating - this is a big security," Christian de Marliave, Tara's scientific director told the BBC last year. "It's become very dangerous."

In 2007, he said, Russian scientists were unable to find ice thick enough to pitch a safe camp. However, the trip onboard Tara was not without difficulties, according to the crew.

"We could feel the ice's strength. It pressed into the boat and made its structure vibrate at each movement," Grant Redvers, the expedition chief, said during the early phases of the venture.

Now in open water, the boat and its crew will take approximately three days to reach Spitsbergen, where Tara will go through routine maintenance before continuing to its home port of Lorient in France.

"Tara is navigating in open water but is still encountering ice remnants," said expedition director Etienne Bourgois.

"[The boat] should touch land before the end of the week."