By David Shukman
BBC science and environment correspondent
The giant Ayles Ice Island drifting off Canada's northern shores has broken in two - far earlier than expected.
The BBC team sets up on Ayles Ice Island
In a season of record summer melting in the region, the two chunks have moved rapidly through the water - one of them covering 98km (61 miles) in a week.
Their progress has been tracked amid fears they could edge west towards oil and gas installations off Alaska.
The original Manhattan-sized berg (16km by five km; 10 miles by three miles) broke off the Ayles Ice Shelf in 2005.
I joined a team that landed on the ice island in May to carry out the first scientific investigation into what many see as a key indicator of global warming.
Pictures from space show the parting of the ice blocks
It is an unsettling thought that the very ice we landed on - and filmed on - for several hours has since ripped apart.
One of the scientists on that mission was Luke Copland of the University of Ottawa, and he told BBC News that the fact that the island had headed south was significant.
"The island became more vulnerable to breaking up with the warmer temperatures in more southerly latitudes, together with having less protection from the smaller amounts of surrounding sea-ice.
"It's relatively unusual for the ice island to drift so far south so quickly - many ice islands in the past have stayed within the Arctic Ocean, or within the northern parts of the Queen Elizabeth Islands."
Dr Copland said that the island had travelled so far south because of the small extent of Arctic ice this summer, influenced in turn by warmer conditions.
"The low sea-ice conditions this year have played a role. The sea-ice normally blocks ice inflow into the Queen Elizabeth Islands, but with less ice this year it has made it easier for the Ice Island to make its way in."
And his conclusion is clear: unlike ice islands which in the past might have lasted in the Arctic Ocean for 50 years or more, this one is destined to be shorter-lived.
"Ultimately, the ice island should break up faster because of the warmer temperatures - I'd be surprised if it lasted more than a decade or so."
Pictured in May, this block of ice has now split into two pieces
The team which landed on the Ayles ice block in May found it to have an average thickness of 42-45m (138-148ft) - the equivalent of the height of a 10-storey building. The great mass of ice has now split apart.
Arctic sea-ice shrank to the smallest area on record this year, as measured by satellite.
The US National Snow and Ice Data Center (NSIDC) said the minimum extent of 4.13 million sq km (1.59 million sq miles) was reached on 16 September.
The figure shattered all previous satellite surveys, including the previous record low of 5.32 million sq km measured in 2005.
Click here to see the Canadian Ice Service website tracking the ice blocks.
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
Limited sea-ice in 2007 has seen the berg move 100s of km