f has split away from Ellesmere Island, according to satellite pictures.
It is thought to be the biggest piece of ice shed in the region since 60 sq km of the nearby Ayles ice shelf broke away in 2005.
Scientists say further splitting could occur during the Arctic summer melt.
The polar north is once again experiencing a rapid ice retreat this year, although many scientists doubt the record minimum extent of 4.13 million sq km (1.59 million sq miles) of sea-ice seen in 2007 will be beaten.
Nonetheless, dramatic changes are occurring in the region, affecting the ice both in the open ocean and the ice which is attached to the coast.
Researchers had predicted that the Ward Hunt Ice Shelf (WHIS) was likely to experience a major calving event of this nature.
Scientists travelling with the Canadian armed forces visited the area recently and found major new fractures in the ice that stretched for more 16km (10 miles).
Ellesmere Island was once bounded by one giant ice shelf that covered almost 10,000 sq km (3,500 sq miles).
Now this expanse of ice has retreated into a string of much smaller, individual shelves, which together cover just under 1,000 sq km (400 sq miles). At 440 sq km (170 sq miles) in size and 40m (130ft) thick, the WHIS is the largest of the remnant shelves. Scientists have been studying the Canadian feature because of what it can tell them about Arctic history.
Radiocarbon dating of drift wood trapped behind the shelf in Disraeli Fjord shows the shelf itself has been in place for at least 3,000 years.
However, an analysis of past records suggests that since the early 20th Century, the ice that makes up the WHIS has retreated by about 90%.
Researchers believe the mechanism which has maintained its stability - fresh water coming out of Disraeli Fjord and freezing under the shelf - may have been disturbed. If that is the case, the rest of the WHIS may disappear quite rapidly, researchers say.
Loss of sea-ice in the Arctic has global implications. The "white parasol" at the top of the planet reflects energy from the Sun straight back out into space, helping to cool the Earth.
Further loss of Arctic ice will see radiation absorbed by darker seawater and snow-free land, potentially warming the Earth's climate at an even faster rate than current observational data indicates.
As with the Ayles breakout in 2005, the authorities will have to track the Ward Hunt ice carefully. Its size means it could be a hazard to shipping and offshore development in the region.