Media playback is unsupported on your device Media caption David Shukman looks at the difficulties of doing scientific research in the Arctic

Changes in the Arctic Ocean are so profound that the region is entering what amounts to "a new era", according to Norwegian scientists.

A switch from a permanent cover of thick ice to a new state where thinner ice vanishes in the summer will have far-reaching implications, they say.

The Norwegian Polar Institute has been mounting an expedition to the Arctic Ocean during the year's coldest months.

Scientists have to brave extreme temperatures and total darkness.

Their aim is to gather data on the condition of the ice as it freezes during the polar winter.

A research vessel, the Lance, has been deployed to an area about 500 miles from the North Pole and allowed to drift with the pack-ice.

The director of the institute, Jan-Gunnar Winther, said that measuring what happens in the winter was vital to improving scenarios for future climate change.

Image caption A major focus of the expedition is to examine the consequences of having less so-called multi-year ice and a greater proportion of younger ice

"We have almost no data from the Arctic Ocean in winter - with few exceptions - so this information is very important to be able understand the processes when the ice is freezing in early winter and we'll also stay here when it melts in the summer," he explained.

"A new era has entered, we are going from old ice to young ice, thinner ice and the climate models used today have not captured this new regime or ice situation.

"So knowing how it is today can improve climate models which again improve the projection for global climate change."

Record lows

This research effort comes as US scientists have reported that the maximum extent of Arctic sea-ice was recorded at its lowest winter level since satellite records began.

A major focus of the expedition is to examine the consequences of the Arctic Ocean having less of the so-called multi-year ice - older, tougher floes which have survived for several years - and a greater proportion of younger ice which is thinner.

Among the researchers investigating the impact of this change on the polar biology is Dr Haakon Hop, who is leading a team of biologists working under the ice.

Image caption Scientists want to understand how the cycles of freeze and melt are changing

"Typically, there's much less life underneath first year ice - multiyear ice is more complex, with more ridging and typically has more animal life," he said.

"So what has been seen around the Arctic is these animals that live underneath the ice - crustaceans, amphipods, and copepods - the biodiversity has gone down and their abundance and biomass have also gone down in the areas that have been measured.

"That is a very serious concern because these animals are important prey items for sea birds feeding on the ice edge and for the marine animals that feed on them."

Complex response

Another biologist taking part in the expedition, Dr Philipp Assmy, said it was important to understand how some species might benefit from the ocean having less ice cover - as more sunlight would allow plankton to flourish - while others would suffer.

"We know that the organisms living in the ocean will actually increase because there will be more light available for them to grow.

"On the other hand, the organisms living within the sea-ice are likely going to decline as their habitat deteriorates and that will have cascading effects on the large charismatic marine mammals we are all familiar with."

Image caption Data gathered from the ice can be used to calibrate measurements from satellites and overflights

The expedition is attempting to provide a comprehensive assessment of all key aspects of this part of the Arctic Ocean.

Dr Polona Itkin has been deploying tracking devices on the ice-floes so that the movement and thinning of the ice can be observed after the expedition ends in June.

"We would like to understand how the sea ice cover in this part of the Arctic is behaving in, let's call it, the new climate.

"We know something about this ice that has been studied over decades but we think now the ice is different and we would like to see how different, and what does it mean for other components of the climate."

The scientists say that data gathered from the ice itself is invaluable as a way of calibrating measurements taken by satellites and overflights.

But the work comes with risks. One is the sheer struggle of operating in freezing conditions. During our visit to the Lance, the temperature regularly fell to -21C with the wind lowering the feel of the cold to -47C.

Another threat is from polar bears, and one approached the ship while we were on board.

In the darkness of the polar winter, Dr Jennifer King was in a small group working under the Lance's floodlights when a bear guard suddenly spotted one of the animals emerging into the light.

"It was 25m away, standing up on a ridge, looking at us, looking like a majestic king of the Arctic - it was very beautiful but the heart stops."

The bear was scared away with flare guns.

A further danger is from the mobility of the pack-ice. During the course of the expedition, while scientists have been deployed on the ice, cracks or "leads" have frequently appeared in the surface or floes have collided creating pressure ridges.

Several times, we saw equipment being winched back from the ice to avoid the risk of it being lost. And once while filming, one floe was being forced above another and we were called back to the ship for our own safety.

According to Jan-Gunnar Winther, the younger ice more prevalent in the Arctic now is more mobile.

"We know that the ice drift is faster now than it was 100 years ago.

"So with thinner ice and less ice, it's more moved around by the wind and the weather. It's more dynamic now, we know that."

The expedition, known as the Norwegian Young Sea ICE cruise, can be followed at www.npolar.no/nice2015