By David Shukman BBC science correspondent, Canadian Arctic

The sediments are cut into thin slices

A new technique to track changes in the extent of Arctic sea ice over the past 1,000 years is being developed by a UK team from the University of Plymouth.

The scientists are studying sediments from the sea bed in the fabled Northwest Passage.

These muds may cast valuable historical light on why some famous expeditions to the region were successful while others were doomed to failure.

The research could also guide computer forecasts of future climate.

The reasoning is that, as with tree rings and coral growth, the thin layers of sediment which build up on the ocean floor act a storehouse of information about the patterns of past conditions.

The Plymouth work is being conducted from the Canadian Coast Guard ship, the Amundsen.

Microscopic clues

In bitterly cold weather, Professor Simon Belt, Dr Guillaume Masse and colleagues are using a box-core - a large metal scoop - to extract the upper layers of mud from the ocean floor.

Significantly, periods of sea ice cover frequently coincide with dramatic changes to human populations due to famines and illnesses Dr Guillaume Masse, University of Plymouth

The sediments are then divided into slices - each slice representing about 15 years' accumulation.

The presence in the mud of a particular kind of lipid - an oil - released by microscopic forms of algae indicates how much ice was present each Arctic spring.

The more of the lipid is found, the more algae there was, and therefore the more sea-ice there may have been in any given period.

The Amundsen is on a science cruise in the Arctic Diary: Northwest Passage Ice melt raises tension Ice data 'shatters record'

Professor Belt says the technique should allow a sea-ice record to be generated stretching back hundreds of years - certainly far further back than the 20-30 years of satellite data so far gathered.

"The satellites show the sea ice retreat in summertime from 1979, but before then there's virtually no record at all. We believe this lipid acts as a fingerprint for past sea ice," he told BBC News.

"The indications are that the natural cycles of change over the past have been very rapid - but the likelihood is that we're now seeing the effects of manmade warming on top of that."

Remarkable resolution

The team's research into sediments off the coast of Iceland has provided a very accurate match with recorded historical accounts of the sea ice there over the past millennium.

Now the aim is to provide a similar insight into the advance and retreat of the ice in the Canadian Arctic.

The mud provides a "proxy" for past climate - just like tree rings

This year's study builds on earlier work in the Northwest Passage two years ago.

Dr Masse said: "Our method for historical sea ice determination not only shows remarkable agreement with known historical events, but it has allowed us to provide some information for periods where records are scarce or absent.

"Significantly, periods of sea ice cover frequently coincide with dramatic changes to human populations due to famines and illnesses."

This work holds out the possibility of identifying ice conditions in particular years - for example in 1845 when the Royal Navy despatched Sir John Franklin on his famous expedition to find the Northwest Passage - a clear route from the Atlantic to the Pacific via the Arctic.

It was one of the largest Imperial ventures of its kind, but ended with the loss of all 129 men, the expedition's two warships becoming locked in the ice for two years running.