Atlantic Ocean: Geography, Geology, and Global Impact

The Atlantic Ocean is the second largest of the world's five oceanic divisions, covering approximately 17% of Earth's total surface and 24% of its water surface area. Historically, it served as the vast divide between the "Old World" of Afro-Eurasia and the "New World" of the Americas during the Age of Discovery. Today, it remains a critical driver of global climate and a hub of international economic activity.

Including its marginal seas, the Atlantic spans 106,460,000 square kilometers (41,100,000 sq mi), representing 23.5% of the global ocean. It is divided into two primary basins: the North Atlantic, covering 41,490,000 square kilometers, and the South Atlantic, covering 40,270,000 square kilometers.

The Aethiopian Ocean depicted in a 1710 French map of Africa

Key Facts

Total Surface Area: Approximately 85,133,000 km² (excluding marginal seas).
Average Depth: 3,646 meters (11,962 ft).
Maximum Depth: 8,376 meters (27,480 ft) at the Milwaukee Deep in the Puerto Rico Trench.
Total Volume: 310,410,900 km³ (including marginal seas).
Shoreline Length: 111,866 km, including marginal seas.

The Atlantic as seen from the shores of Clare Island, Ireland, in 1981

Bathymetry and Geological Structure

The bathymetry (the measurement of depth in oceans) of the Atlantic is dominated by the Mid-Atlantic Ridge (MAR), a massive submarine mountain range. The MAR extends from 300 km south of the North Pole down to Bouvet Island at 54°S.

False color map of ocean depth in the Atlantic basin

The Mid-Atlantic Ridge

The MAR rises 2–3 km above the surrounding ocean floor. It serves as a divergent plate boundary, where the North American and Eurasian plates separate in the north, and the South American and African plates separate in the south. This geological activity produces pillow lava on the ocean floor and basaltic volcanoes, such as Eyjafjallajökull in Iceland. While the apex of the ridge is typically shallower than 2,700 meters, the base of the ridge is three times deeper.

Visualisation of the Gulf Stream stretching from the Gulf of Mexico to Western Europe — As the Gulf Stream meanders across the North Atlantic from the North American east coast to Western Europe its temperature drops by 20 °C (36 °F).

Water Characteristics and Circulation

The Atlantic is characterized by complex water masses categorized by temperature and salinity. These masses are distributed across upper waters (0–500 m), intermediate waters (500–1,500 m), and deep/abyssal waters (1,500 m to the bottom).

Atlantic Ocean Water Mass Characteristics
Water Layer	Water Mass	Temperature Range	Salinity Range
Upper (0–500m)	Atlantic Subarctic Upper Water (ASUW)	0.0–4.0 °C	34.0–35.0
Western North Atlantic Central Water (WNACW)	7.0–20 °C	35.0–36.7
Eastern North Atlantic Central Water (ENACW)	8.0–18.0 °C	35.2–36.7
South Atlantic Central Water (SACW)	5.0–18.0 °C	34.3–35.8
Intermediate (500–1,500m)	Western Atlantic Subarctic Intermediate Water (WASIW)	3.0–9.0 °C	34.0–35.1
Eastern Atlantic Subarctic Intermediate Water (EASIW)	3.0–9.0 °C	34.4–35.3
Mediterranean Water (MW)	2.6–11.0 °C	35.0–36.2
Arctic Intermediate Water (AIW)	−1.5–3.0 °C	34.7–34.9
Deep/Abyssal (1,500m+)	North Atlantic Deep Water (NADW)	1.5–4.0 °C	34.8–35.0
Antarctic Bottom Water (AABW)	−0.9–1.7 °C	34.6–34.7
Arctic Bottom Water (ABW)	−1.8 to −0.5 °C	34.9–34.9

Map displaying a looping line with arrows indicating that water flows eastward in the far Southern Ocean, angling northeast of Australia, turning sough-after passing Alaska, then crossing the mid-Pacific to flow north of Australia, continuing west below Africa, then turning northwest until reaching eastern Canada, then angling east to southern Europe, then finally turning south just below Greenland and flowing down the Americas' eastern coast, and resuming its flow eastward to complete the circle — Path of the thermohaline circulation. Purple paths represent deep-water currents, while blue paths represent surface currents.

Ocean Gyres and Currents

The Atlantic features major gyres—large systems of circulating ocean currents. In the North Atlantic, warm subtropical waters are transformed into colder subpolar and polar waters within the subpolar gyre. The Gulf Stream is a prominent current that transports warm water from the North American coast toward Western Europe, dropping in temperature by approximately 20 °C (36 °F) during its journey.

In the subpolar gyre of the North Atlantic warm subtropical waters are transformed into colder subpolar and polar waters. In the Labrador Sea this water flows back to the subtropical gyre.

Climate and Natural Hazards

The Atlantic is a primary site for the formation of hurricanes. These are often triggered by instabilities in the atmosphere created by waves in the trade winds—areas where converging winds move along the same track as the prevailing wind.

Map of Caribbean showing seven approximately parallel westward-pointing arrows that extend from east of the Virgin Islands to Cuba. The southern arrows bend northward just east of the Dominican Republic before straightening out again. — Waves in the trade winds in the Atlantic Ocean – areas of converging winds that move along the same track as the prevailing wind – create instabilities in the atmosphere that may lead to the formation of hurricanes.

Human History and Economic Impact

The Atlantic has been central to global history, from the limited Norse knowledge of the Americas described in the Íslendingasögur sagas to the Portuguese discoveries influenced by Atlantic gyres. However, this history also includes the Atlantic slave trade between 1525 and 1863.

Iceberg A22A in the South Atlantic Ocean

Excavation of the Ertebølle middens in 1880

Based on the medieval Íslendingasögur sagas, including the Grœnlendinga saga, this interpretative map of the "Norse World" shows that Norse knowledge of the Americas and the Atlantic remained limited.

The Atlantic Gyres influenced the Portuguese discoveries and trading port routes, here shown in the India Run ("Carreira da Índia"), which would be developed in subsequent years.

Embarked and disembarked slaves in the Atlantic slave trade 1525–1863 (first and last slave voyages)

Fisheries and Marine Resources

The ocean provides vast fishing grounds, particularly in the northeast and northwest Atlantic. In the southeast Atlantic, catches of horse mackerel and hake are most significant. While some regions saw declines—such as catches dropping from 3.3 million tons in the early 1970s to 1.3 million tons in 2013—regulations introduced in 2006 have helped recover deep-water and shallow-water hake to sustainable levels off South Africa and Namibia.

Capture of Atlantic northwest cod in million tons

Environmental Challenges

The Atlantic faces significant environmental threats, including marine debris and pollution. This is evident on remote locations such as the South Atlantic's Inaccessible Island, where waste often washes ashore.

Marine debris strewn over the beaches of the South Atlantic Inaccessible Island

Frequently Asked Questions

What is the deepest point of the Atlantic Ocean?

The deepest point is the Milwaukee Deep, located in the Puerto Rico Trench, reaching a depth of 8,376 meters (27,480 ft).

What is the Mid-Atlantic Ridge?

The Mid-Atlantic Ridge is a submarine mountain range that forms a divergent plate boundary, separating the Americas from Europe and Africa.

How does the Gulf Stream affect temperature?

The Gulf Stream carries warm water from the North American east coast to Western Europe, though its temperature drops by about 20 °C (36 °F) along the way.

What causes hurricanes in the Atlantic?

Hurricanes are often caused by atmospheric instabilities created by waves in the trade winds, where converging winds move along the same track as prevailing winds.

Are Atlantic fisheries sustainable?

Sustainability varies by region. While some areas experienced declines, regulations introduced in 2006 have helped recover hake populations to sustainable levels in the southeast Atlantic.