By David Shukman
Eureka High Arctic Weather Station, Canada
Scientists in the Arctic have just carried out the first research on a huge iceberg the size of Manhattan.
Some 16km long and 5km wide (10x3 miles), Ayles Ice Island broke away from the Canadian Arctic coast in 2005, but has only recently been identified.
Researchers have now landed on the giant berg with a BBC team and planted a tracking beacon on its surface.
This will allow the island's progress to be monitored as currents push it around the Arctic Ocean.
For 3,000 years, this colossal block of ice was securely fixed to the coast as part of the Ayles Ice Shelf - but now it is drifting free.
Its current location is about 600km (400 miles) from the North Pole, in what is one of the fastest warming regions on Earth.
We approached the island in a small plane. From the air, the vast expanse of white stood out as unusually smooth compared with the much rougher sea ice that forms and thaws with the changing seasons.
The island's surface was judged safe enough to land on - our plane was fitted with skis - and after a bumpy touchdown we ground to a halt, the first expedition of its kind.
Soon the scientists were at work - time was limited with the risk of the weather changing.
First, Dr Derek Mueller of the University of Alaska Fairbanks dug down through the surface layer of snow to reach the mass of the ice below.
Then he and Dr Luke Copland, of the University of Ottawa, carried out a series of measurements using a ground-penetrating radar.
They found that the average of thickness of the ice was 42-45m (138-148ft) - the equivalent of the height of a 10-storey building.
This was slightly thicker than expected.
One implication is that the island is may prove even more durable than predicted - the sheer weight of ice estimated at two billion tonnes may take longer to melt than initially thought.
But according to Dr Copland, the fact that such thick ice could split apart in less than an hour - as it did back in August 2005 - illustrates a more alarming point.
From above, the island appears flat against the jagged sea ice
"This shows how climate change can trigger very sudden changes even on a massive scale - when the ice shelf broke away, the rupture registered with the force of a small earthquake," he said.
The records show that this region of the Arctic - the northern coast of Ellesmere Island - has lost 90% of its ice shelves in the past century.
Much of this occurred during the warmer period of the 1940s but then in the cooler decades that followed, some of the ice shelves showed signs of reforming.
According to Dr Mueller, "the difference now is that with the current rate of warming, those ice shelves are likely never to be reconstituted".
Climate scientists predict that the Arctic will continue to warm - so the expectation is that the five remaining ice shelves here could also break away. The effect already is that the map of the Arctic will have to be redrawn.
Before we left, the scientists planted a satellite tracking beacon - because if the island continues to drift to the west, it could threaten the oil and gas installations off Alaska.
Click here to see the Canadian Ice Service website tracking the beacon's location.
The Ayles Ice Island calved off the Ayles Ice Shelf in August 2005
The calving event was the largest in at least the last 25 years
A total of 87.1 sq km (33.6 sq miles) of ice was lost in this event
The largest piece was 66.4 sq km (25.6 sq miles) in area
This made the slab a little larger than Manhattan
Ayles Ice Island has moved some 50km (30 miles) since calving