<Li> <P> The Blue Marble, Earth as seen from Apollo 17 with the southern polar ice cap visible (courtesy NASA) </P> </Li> <P> The Blue Marble, Earth as seen from Apollo 17 with the southern polar ice cap visible (courtesy NASA) </P> <P> Earth's North Pole is covered by floating pack ice (sea ice) over the Arctic Ocean . Portions of the ice that do not melt seasonally can get very thick, up to 3--4 meters thick over large areas, with ridges up to 20 meters thick . One - year ice is usually about 1 meter thick . The area covered by sea ice ranges between 9 and 12 million km2 . In addition, the Greenland ice sheet covers about 1.71 million km2 and contains about 2.6 million km3 of ice . When the ice breaks off (calves) it forms icebergs scattered around the northern Atlantic . </P> <P> According to the National Snow and Ice Data Center, "since 1979, winter Arctic ice extent has decreased about 4.2 percent per decade". Both 2008 and 2009 had a minimum Arctic sea ice extent somewhat above that of 2007 . At other times of the year the ice extent is still sometimes near the 1979--2000 average, as in April 2010, by the data from the National Snow and Ice Data Center . Still, between these same years, the overall average ice coverage appears to have declined from 8 million km2 to 5 million km2 . </P>

How deep is the ice at the north pole