A phenomenon called Arctic sea ice decline can be shown on the islands: In the 20th century, the islands were a portion of Eurasia which was always covered by ice. Even as the ice melted in summer, some of the ice remained, and blocked what is called the Northeast Passage. If it were ice free the Northeast passage would permit to naviagate from the Atlantic to the Pacific Ocean easily. By the late summer of 2012, the permanent ice had reached a record low extent and open water appeared to the north of the archipelago.