Atlantic Ocean

The Atlantic Ocean is the second-largest of the Earth’s five oceanic divisions, covering approximately 85,133,000 km² (32,870,000 sq mi), which represents about 17% of Earth’s total surface and nearly 24% of the world’s water surface area. It occupies an elongated S-shaped basin stretching from the Arctic Ocean in the north to the Southern Ocean (or Antarctica) in the south and is flanked by Europe and Africa to the east and the Americas to the west. As a central component of global navigation and trade, the Atlantic has profoundly shaped the political, economic, and cultural evolution of the modern world.

Etymology and Early References

The term “Atlantic” originates from the ancient Greek expression Atlantikôi pelágei (“Sea of Atlas”), first mentioned by the poet Stesichorus around the 6th century BCE and later by Herodotus in his Histories (c. 450 BCE) as Atlantis thalassa, referring to the sea “beyond the pillars of Hercules” (the Strait of Gibraltar). In Greek mythology, Atlas, the Titan condemned to hold up the sky, lent his name to the ocean and later to the mountain range in North Africa.
In the Middle Ages, cartographers sometimes called it the “Aethiopian Ocean”, particularly for its southern reaches, while 16th–17th-century English explorers referred to it as the “Great Western Ocean.” The colloquial phrase “across the pond”, used by Britons and Americans today, reflects the Atlantic’s enduring role as a bridge between the Old and New Worlds.

Geography and Extent

The Atlantic Ocean extends between Europe and Africa on the east and North and South America on the west. It connects:

• northward to the Arctic Ocean via the Labrador Sea, Denmark Strait, and Greenland Sea;
• southward to the Southern Ocean or Antarctica;
• southeastward to the Indian Ocean (via the 20°E meridian through Cape Agulhas);
• southwestward to the Pacific Ocean through the Drake Passage and Magellan Strait.

Including its marginal seas, the Atlantic spans 106.46 million km² (41.1 million sq mi) and holds about 310 million km³ (23.3%) of the global ocean volume. Excluding these seas, it covers 81.76 million km². Its average depth is 3,646 m (11,962 ft), and the deepest point is the Milwaukee Deep in the Puerto Rico Trench, reaching 8,376 m (27,480 ft).
The Atlantic is subdivided by the Equator into two major sections:

• North Atlantic Ocean, covering 41.49 million km².
• South Atlantic Ocean, covering 40.27 million km².

Bathymetry and Ocean Floor

The Mid-Atlantic Ridge

The defining geological feature of the Atlantic basin is the Mid-Atlantic Ridge (MAR), a massive submarine mountain chain running roughly north–south from 87°N, near the Arctic, to 54°S, near Bouvet Island. Rising 2–3 km above the abyssal plains, it divides the ocean into eastern and western halves. The ridge is a divergent plate boundary separating the North American and Eurasian Plates in the north and the South American and African Plates in the south.
The MAR is segmented by major fracture zones, notably the Romanche Trench near the Equator and the Gibbs Fracture Zone near 53°N, which allow deep-water flow between basins. In places such as Iceland, the ridge emerges above sea level, producing volcanic activity like that of Eyjafjallajökull.
The discovery of the MAR in the late 19th century during the Challenger Expedition and its further mapping in the 1920s by the German Meteor Expedition were pivotal in the eventual formulation of plate tectonic theory in the mid-20th century.

Continental Shelves and Abyssal Plains

The continental shelves of the Atlantic vary greatly in width — extensive off Newfoundland, northeast Europe, and southern South America. Major submarine features include the Blake Plateau, Bermuda Rise, and Laurentian Abyss. Deep trenches occur mainly at active plate margins such as the Puerto Rico Trench and South Sandwich Trench.
Abyssal plains dominate the deeper ocean floor, interspersed with seamounts and plateaus. Mapping advances such as the 1922 USS Stewart sonar survey provided the first continuous profiles of the Atlantic seabed.

Water Characteristics and Circulation

Temperature and Salinity

Surface temperatures in the Atlantic range from below −2 °C in polar regions to above 30 °C in tropical zones, with the warmest waters found north of the Equator. The Atlantic is the saltiest of all major oceans, averaging 33–37 parts per thousand (ppt). High salinity in subtropical latitudes results from intense evaporation, while lower salinity near the Equator and poles is due to precipitation and ice melt.

Major Currents and Gyres

The Atlantic features two primary gyres:

• North Atlantic Gyre – a clockwise system including the Gulf Stream, North Atlantic Current, Canary Current, and North Equatorial Current.
• South Atlantic Gyre – an anticlockwise system formed by the Brazil Current, Benguela Current, and South Equatorial Current.

The Gulf Stream transports warm Caribbean waters northeastward, moderating the climate of Western Europe through its extension, the North Atlantic Drift. The South Atlantic Current links with the Indian Ocean via the Agulhas Leakage, balancing salinity and heat exchange between basins.

Thermohaline Circulation

Deep circulation in the Atlantic is governed by thermohaline processes, notably the formation of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). Dense, saline surface waters sink in the Labrador and Norwegian Seas, driving the Atlantic Meridional Overturning Circulation (AMOC) — a critical global conveyor of heat and carbon.
Recent studies indicate that the AMOC has weakened by about 12–15% since the mid-20th century, potentially linked to anthropogenic climate change. A continued slowdown could significantly alter North Atlantic climate patterns.

The Sargasso Sea

Located within the North Atlantic subtropical gyre, the Sargasso Sea is a unique region characterized by floating Sargassum seaweed (species S. fluitans and S. natans). Bounded by ocean currents rather than land, it spans approximately 4,000 km across. It supports distinctive ecosystems and serves as the spawning ground for both European and American eels, whose larvae drift with the Gulf Stream before returning to continental waters.

Climate and Natural Hazards

The Atlantic’s influence on global climate is profound. The Gulf Stream and North Atlantic Drift maintain milder winters in northwest Europe, while cold currents such as the Labrador and Canary Currents cool adjacent coasts. The ocean is also a major moisture source, driving the formation of hurricanes, particularly in the Caribbean and Gulf of Mexico.
The North Atlantic Oscillation (NAO) governs much of the variability in European and North American climate, alternating between wet, mild phases and dry, cold ones. Icebergs drifting from Greenland and frequent fog banks (notably near the Grand Banks of Newfoundland) pose navigational hazards.

Geological Evolution

The Atlantic formed about 200 million years ago during the breakup of Pangaea, initiated by the Central Atlantic Magmatic Province (CAMP) eruptions. Rifting began between North America and Northwest Africa, eventually producing new oceanic crust and separating the continents.
In the Cretaceous Period, the South Atlantic opened as South America and Africa drifted apart. Subsequent rifting created the Mid-Atlantic Ridge and expanded the basin. The closure of the Central American Seaway around 2.8 million years ago, when the Isthmus of Panama rose, profoundly altered ocean circulation, intensifying the Gulf Stream and reshaping global climate.
Today, subduction zones such as those near the Caribbean and Gibraltar may signal the beginning of a new Wilson Cycle, gradually leading to the Atlantic’s eventual closure over tens of millions of years.

Human History and Exploration

Early Crossings

While Norse explorers reached Greenland and Vinland (Newfoundland) around 1000 CE, large-scale transatlantic interaction began with Christopher Columbus’s voyage in 1492. This marked the start of the Age of Discovery, connecting Europe, Africa, and the Americas.

The Atlantic World

Between the 15th and 19th centuries, the Atlantic became the hub of global commerce and colonization. It hosted:

• The Columbian Exchange, transferring crops, animals, and diseases between hemispheres.
• The Atlantic slave trade, forcibly transporting over 9 million Africans to the Americas between 1525 and 1888.
• Naval rivalries and imperial expansion by Spain, Portugal, France, Britain, and the Netherlands.

By the 18th century, Atlantic trade had surpassed Mediterranean commerce in volume and profitability, fueling urbanisation and industrial growth in Western Europe.

Modern Era

The Atlantic remained a central theatre in both World Wars, notably during the Battle of the Atlantic (1939–45). In the post-war period, it became a zone of economic cooperation under organisations like NATO and the Atlantic Alliance. Today, it continues to facilitate transatlantic trade and communication, with submarine cables forming the backbone of global internet connectivity.

Economy and Resources

The Atlantic supports vast economic activity, including:

• Petroleum and natural gas extraction from continental shelf basins (e.g., North Sea, Gulf of Mexico, offshore Brazil, and West Africa).
• Major fisheries, particularly in the Grand Banks, North Sea, Scotian Shelf, and Falkland Banks.
• Shipping routes linking the world’s major ports, including New York, Rotterdam, Hamburg, Lagos, Buenos Aires, and Cape Town.

The ocean’s resources also include polymetallic nodules, aggregates, and precious minerals, though many remain economically unviable for deep-sea mining.

Environmental Issues

Overfishing

Fish stocks in many Atlantic regions have declined severely. The Northwest Atlantic cod fishery, once among the world’s richest, collapsed in the early 1990s due to overexploitation. Recovery remains partial despite regulatory measures. About 30–45% of Atlantic fish stocks are now considered overfished.

Pollution and Waste

Pollution from industrial discharges, oil spills, and agricultural runoff has created hypoxic “dead zones”, notably in the Gulf of Mexico and Baltic Sea. The North Atlantic Garbage Patch, composed largely of microplastics, spans hundreds of kilometres. Nuclear materials and chemical wastes dumped in past decades persist on the seafloor.

Climate Change

Rising ocean temperatures have increased North Atlantic hurricane activity and altered fish migration patterns. Melting of Greenland’s ice sheet and thermal expansion contribute to sea-level rise, while the weakening of the AMOC threatens to disrupt regional climates further.