National Geographic : 2009 May
SEARCHING FOR THE EDGES OF CONTINENTS THE SEAFLOOR'S CONTOURS Until recently, charts of submarine features in the icebound north were sketchy. Now a different world is emerging, as mapping expeditions with high-tech tools reveal areas that are much higher or lower than previously believed (below). Such details are crucial: A country must describe the shape of the seabed and the thickness of sediment to support its claims. Foot of continental slope 2,500-meter depth Shore Thickness of sediment Sedimentary rock RUSSIA NOR WAY ICELA ND (GREENLAND) DENMARK CANADA U.S. (ALASKA) North Pole ARCTIC CIRCLE Lower Higher Same 2,000 1,000 0 1,000 2,000 3,000 meters MAP AND GRAPHIC BY BILL RANKIN SOURCES: IBCAO AND NATIONAL GEOPHYSICAL DATA CENTER NGDC , NOAA SEAFLOOR ELEVATION ; IBRU, DURHAM UNIVERSITY BOUNDARIES ; UNITED NATIONS CONVENTION ON THE LAW OF THE SEA GRAPHIC 1 NAUTICAL MILE = 1.15 STATUTE MILES Continental shelf claims cannot extend beyond: Compared with 1970s data, the elevation of the seafloor is now thought to be: 350 nautical miles from the shore or 100 nm past a water depth of 2,500 meters. Within these standards, claims are further limited to: 60 nm from the foot of the continental slope or a minimum thickness of sediment.