Two ice shelves in Canada's far north have lost massive sections since August, while a third ice shelf is now adrift in the Arctic Ocean.
The entire 50 sq km Markham Ice Shelf off the coast of Ellesmere Island broke away in early August and is now adrift, while two sections of the nearby Serson Ice Shelf detached, reducing its mass by 60% or 122 sq km.
Ward Hunt Ice Shelf, which halved in July, lost an additional 22 sq km.
Trent University polar expert Derek Mueller blamed climate change, and said ice shelf changes were irreversible under the present climate.
"(The changes) indicate that the environmental conditions that have kept these ice shelves in balance for 4,000 years are no longer present," he said.
Canada's summer ice shelf losses now total 214 sq km, which is more than three times the area of Manhattan Island.
Extensive cracks in Ward Hunt, the largest remaining ice shelf, means it will continue to disintegrate in the coming years, said Luke Copland, director Ottawa University's cryospheric research lab.
The Ellesmere ice shelves were formed some 4,500 years ago, composed of sea ice, accumulated snow and glacier ice up to 40m thick.
The detached pieces broke into numerous 'ice islands' (tabular icebergs) whose fate could take many forms, said researchers.
The Canadian Ice Service is tracking the broken pieces.