Editing Atlantic Ocean (section)

== Bathymetry ==
[[File:Atlantic bathymetry.jpg|thumb|[[False color]] map of ocean depth in the Atlantic basin]]
The [[bathymetry]] of the Atlantic is dominated by a [[Mid-ocean ridge|submarine mountain range]] called the [[Mid-Atlantic Ridge]] (MAR). It runs from 87°N or {{cvt|300|km}} south of the [[North Pole]] to the subantarctic [[Bouvet Island]] at [[54th parallel south|54°S]].<ref name="WHC-MAR">{{Harvnb|World Heritage Centre: Mid-Atlantic Ridge}}</ref> Expeditions to explore the bathymertry of the Atlantic include the [[Challenger expedition|''Challenger'' expedition]] and the [[German Meteor expedition|German ''Meteor'' expedition]]; {{As of|2001|lc=y}}, [[Columbia University]]'s [[Lamont–Doherty Earth Observatory]] and the [[United States Navy Hydrographic Office]] conduct research on the ocean.<ref name="USN-2001" />

=== Mid-Atlantic Ridge ===
{{Main|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 {{cvt|2000|m}} 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 [[53rd parallel north|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.<ref name="LevGood-2003">{{Harvnb|Levin|Gooday|2003|loc=Seafloor topography and physiography, pp. 113–114}}</ref>

The MAR rises {{cvt|2|-|3|km}} above the surrounding ocean floor and its [[rift valley]] is the [[divergent boundary]] between the [[North American plate|North American]] and [[Eurasian plate|Eurasian]] plates in the North Atlantic and the [[South American plate|South American]] and [[African plate|African]] plates in the South Atlantic. The MAR produces [[Basaltic lava|basaltic volcanoes]] in [[Eyjafjallajökull]], Iceland, and [[pillow lava]] on the ocean floor.<ref>{{Harvnb|The Geological Society: Mid-Atlantic Ridge}}</ref> The depth of water at the apex of the ridge is less than {{cvt|2700|m|fathom ft|lk=out}} in most places, while the bottom of the ridge is three times as deep.<ref>{{Cite book|title=The Mediterranean Was a Desert: A Voyage of the Glomar Challenger|last=Kenneth J. Hsü|year=1987|publisher=Princeton University Press|isbn=978-0-691-02406-6}}</ref>

The MAR is intersected by two perpendicular ridges: the [[Azores–Gibraltar transform fault]], the boundary between the [[Nubian plate|Nubian]] and [[Eurasian plate]]s, intersects the MAR at the [[Azores triple junction]], on either side of the Azores microplate, near the [[40th parallel north|40°N]].<ref>{{Harvnb|DeMets|Gordon|Argus|2010|loc=The Azores microplate, pp. 24–25}}</ref> 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 [[16th parallel north|16°N]].<ref>{{Harvnb|DeMets|Gordon|Argus|2010|loc=Boundary between the North and South America plates, pp. 26–27}}</ref>

In the 1870s, the [[Challenger expedition|''Challenger'' expedition]] discovered parts of what is now known as the Mid-Atlantic Ridge, or:
{{Blockquote|text=An elevated ridge rising to an average height of about {{cvt|1900|fathom|m ft|disp=sqbr}} below the surface traverses the basins of the North and South Atlantic in a meridianal direction from Cape Farewell, probably its far south at least as Gough Island, following roughly the outlines of the coasts of the Old and the New Worlds.<ref>{{Harvnb|Thomson|1877|p=290}}</ref>}} The remainder of the ridge was discovered in the 1920s by the [[German Meteor expedition|German ''Meteor'' expedition]] using echo-sounding equipment.<ref>{{Harvnb|NOAA: Timeline}}</ref> The exploration of the MAR in the 1950s led to the general acceptance of [[seafloor spreading]] and [[plate tectonics]].<ref name="WHC-MAR" />

Most of the MAR runs under water but where it reaches the surfaces it has produced volcanic islands. While nine of these have collectively been nominated a [[World Heritage Site]] for their geological value, four of them are considered of "Outstanding Universal Value" based on their cultural and natural criteria: [[Þingvellir National Park|Þingvellir]], Iceland; [[Landscape of the Pico Island Vineyard Culture]], Portugal; [[Gough and Inaccessible Islands]], United Kingdom; and Brazilian Atlantic Islands: [[Fernando de Noronha]] and [[Atol das Rocas]] Reserves, Brazil.<ref name="WHC-MAR" />

=== Ocean floor ===
{{For|a list of fracture zones in the Atlantic|List of fracture zones#Atlantic Ocean}}
[[Continental shelf|Continental shelves]] in the Atlantic are wide off Newfoundland, southernmost South America, and northeastern Europe.
In the western Atlantic [[carbonate platform]]s dominate large areas, for example, the [[Blake Plateau]] and [[Bermuda Rise]].
The Atlantic is surrounded by [[passive margin]]s except at a few locations where [[active margin]]s form deep [[oceanic trench|trenches]]: the [[Puerto Rico Trench]] ({{cvt|8376|m|disp=or}} maximum depth) in the western Atlantic and [[South Sandwich Trench]] ({{cvt|8264|m|disp=or}}) 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.<ref name="LevGood-2003" />

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.<ref name="the Atlantic">{{Cite book|title=The Great Deep|last=Hamilton-Paterson|first=James|date=1992|author-link=James Hamilton-Paterson}}</ref> The deep ocean floor is thought to be fairly flat with occasional deeps, [[abyssal plain]]s, [[oceanic trench|trenches]], [[seamount]]s, [[Oceanic basin|basins]], [[Oceanic plateau|plateaus]], [[Submarine canyon|canyons]], and some [[guyot]]s. 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 [[60th parallel north|60°N]] and [[60th parallel south|60°S]] is {{cvt|3730|m}}, or close to the average for the global ocean, with a modal depth between {{cvt|4000|and|5000|m}}.<ref name="LevGood-2003" />

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.