Editing Atlantic Ocean (section)

== Marine environment ==
Biological productivity differs considerably across the Atlantic. Much of the open subtropical ocean contains limited surface nutrients because warm water resists vertical mixing. Productivity increases where currents bring deeper water toward the surface. Upwelling associated with the Benguela Current supports large fish populations off southwestern Africa. Similar conditions occur along the northwestern African coast.

Continental shelves receive nutrients from rivers and mixing near the seabed. These shallow waters support important fisheries. Estuaries provide sheltered habitats where fresh water mixes with seawater. Tropical Atlantic waters contain coral reefs where temperatures and light conditions permit coral growth. Colder parts of the ocean contain deep-water coral communities that do not depend on sunlight.

The deep Atlantic supports organisms adapted to darkness and high pressure. Hydrothermal vents occur along the Mid-Atlantic Ridge where seawater enters cracks in hot oceanic crust. Heated water dissolves minerals before returning to the seabed. Chemical reactions around the vents provide energy for biological communities that do not depend directly on sunlight.