section_path: Bathymetry/Ocean floor
section_name: Ocean floor
paragraph_text: Ocean floor
  
  Continental shelves in the Atlantic are wide off Newfoundland, southernmost South America, and northeastern Europe.In the western Atlantic carbonate platforms dominate large areas, for example, the Blake Plateau and Bermuda Rise.The Atlantic is surrounded by passive margins except at a few locations where active margins form deep trenches: the Puerto Rico Trench (8,376 m or 27,480 ft maximum depth) in the western Atlantic and South Sandwich Trench (8,264 m or 27,113 ft) in the South Atlantic. There are numerous submarine canyons off northeastern North America, western Europe, and northwestern Africa. Some of these canyons extend along the continental rises and farther into the abyssal plains as deep-sea channels.
  
  In 1922, a historic moment in cartography and oceanography occurred. The USS Stewart used a Navy Sonic Depth Finder to draw a continuous map across the bed of the Atlantic. This involved little guesswork because the idea of sonar is straightforward with pulses being sent from the vessel, which bounce off the ocean floor, then return to the vessel. The deep ocean floor is thought to be fairly flat with occasional deeps, abyssal plains, trenches, seamounts, basins, plateaus, canyons, and some guyots. Various shelves along the margins of the continents constitute about 11% of the bottom topography with few deep channels cut across the continental rise.
  
  The mean depth between 60°N and 60°S is 3,730 m (12,240 ft), or close to the average for the global ocean, with a modal depth between 4,000 and 5,000 m (13,000 and 16,000 ft).
  
  In the South Atlantic the Walvis Ridge and Rio Grande Rise form barriers to ocean currents.The Laurentian Abyss is found off the eastern coast of Canada.