Most of the traditional impressions people have about Canada's Arctic are defined by the Arctic Basin Ecozone. This is essentially the parts of the Arctic Ocean that remain under permanent ice cover. It extends from the southern edge of the permanent ice line in the Beaufort Sea north and east over the Canada Basin of the northern tip of Greenland. It skirts the northern edge of the Queen Elizabeth Islands and touches the northern coast of Ellesmere Island. The overwhelming ecological characteristic of this ecozone is the constant cover of ice sheets and pack ice. More than 90% of the region consists of a giant permanent ice cap floating on the ocean. It slowly rotates in a counter-clockwise pattern, roughly centred on the North Pole. The rotation is driven by the Arctic Ocean Gyre, one of the main ocean currents. The heavily ridged ice reaches a thickness of 2 metres or more and islands of ice several kilometres square are common.