km2 Irish Sea - 46,000 km2 Sea of Azov - 39,000 km2 Bothnian Bay - 36,800 km2 Gulf of Venezuela - 17,840 km2 Bay of Campeche - 16,000 km2 Gulf of Lion - 15,000 km2 Sea of Marmara - 11,350 km2 Wadden Sea - 10,000 km2 Archipelago Sea - 8,300 km2 Bathymetry The bathymetry of the Atlantic is dominated by a submarine mountain range called the Mid-Atlantic Ridge (MAR). It runs from 87°N or south of the North Pole to the subantarctic Bouvet Island at 54°S. Expeditions to explore the bathymertry of the Atlantic include the Challenger expedition and the German Meteor expedition; presently, Columbia University's Lamont–Doherty Earth Observatory and the United States Navy Hydrographic Office conduct research on the ocean. Mid-Atlantic Ridge The MAR divides the Atlantic longitudinally into two halves, in each of which a series of basins are delimited by secondary, transverse ridges. The MAR reaches above along most of its length, but is interrupted by larger transform faults at two places: the Romanche Trench near the Equator and the Gibbs Fracture Zone at 53°N. The MAR is a barrier for bottom water, but at these two transform faults deep water currents can pass from one side to the other. The MAR rises above the surrounding ocean floor and its rift valley is the divergent boundary between the North American and Eurasian plates in the North Atlantic and the South American and African plates in the South Atlantic. The MAR produces basaltic volcanoes in Eyjafjallajökull, Iceland, and pillow lava on the ocean floor. The depth of water at the apex of the ridge is less than in most places, while the bottom of the ridge is three times as deep. The MAR is intersected by two perpendicular ridges: the Azores–Gibraltar Transform Fault, the boundary between the Nubian and Eurasian plates, intersects the MAR at the Azores Triple Junction, on either side of the Azores microplate, near the 40°N. A much vaguer, nameless boundary, between the North American and South American plates, intersects the MAR near or just north of the Fifteen-Twenty Fracture Zone, approximately at 16°N. In the 1870s, the Challenger expedition discovered parts of what is now known as the Mid-Atlantic Ridge, or: The remainder of the ridge was discovered in the 1920s by the German Meteor expedition using echo-sounding equipment. The exploration of the MAR in the 1950s led to the general acceptance of seafloor