A chunk of ice shelf nearly the size of Manhattan has broken away from Ellesmere Island in Canada's northern Arctic, another dramatic indication of how warmer temperatures are changing the polar frontier, scientists said Wednesday. Derek Mueller, an Arctic ice shelf specialist at Trent University in Ontario, told The Associated Press that the 4,500-year-old Markham Ice Shelf separated in early August and the 19-square-mile shelf is now adrift in the Arctic Ocean. "It was a shocking event that underscores the rapidity of changes taking place in the Arctic," said Muller. Muller also said that two large sections of ice detached from the Serson Ice Shelf, shrinking that ice feature by 47 square miles — or 60 percent — and that the Ward Hunt Ice Shelf has also continued to break up, losing an additional eight square miles.