Imagery acquired by the Expedition 29 crew aboard the International Space Station traces a ground track beginning just northeast of Newfoundland, crossing the North Atlantic and continuing southward across the basin into central Africa over South Sudan, illustrating the ocean’s longitudinal extent and north–south orientation. The Atlantic is the planet’s second-largest oceanic division, covering about 85,133,000 km2—roughly 17% of Earth’s surface and about 24% of its water-covered area. Geomorphologically it occupies an elongated, S-shaped basin bounded to the east by Europe and Africa and to the west by North and South America, producing the characteristic meridional curvature evident on global maps.

As part of the interconnected World Ocean, the Atlantic is oceanographically continuous with the Arctic to the north, the Pacific to the southwest, the Indian Ocean to the southeast and, by some definitions, the Southern Ocean to the south (extending to Antarctic coasts). It is conventionally divided by the Equator into the Northern and Southern Atlantic basins, which exhibit distinct climatic, oceanographic and biogeographic regimes. Sea-surface temperatures and climate differ markedly between them: the South Atlantic remains warm year‑round because much of its basin lies within tropical latitudes, whereas the North Atlantic has a temperate, highly seasonal climate capable of both extreme cold and heat.

Human interactions with the Atlantic have profoundly shaped global history. Although Norse voyages represent the earliest known transatlantic crossings, Christopher Columbus’s 1492 voyage initiated sustained European exploration and colonization by powers such as Portugal, Spain, France and the United Kingdom. From the 16th through the 19th centuries the Atlantic served as the principal conduit for the transatlantic slave trade and the Columbian exchange and was the stage for recurring naval engagements. In the early 20th century, naval activity and commercial traffic increased alongside the rise of regional American powers (notably the United States and Brazil). While the ocean has seen no major military conflicts in recent decades, it remains a central artery of global maritime trade.

The name "Atlantic" derives from Greek literary and mythic traditions in which the waters beyond the Strait of Gibraltar were associated with the Titan Atlas. Early Greek writers applied an Atlas-related appellation to the sea adjacent to the Atlas Mountains and the West African coast; in classical cosmography this body of water was conceived as part of a circumambient world-ocean (Oceanus) rather than as a bounded ocean basin in the modern sense. The association with Atlas persisted iconographically and lexically, ultimately informing not only the ocean's name but also the later cartographic genre of the atlas.

Historically, European mapping and nomenclature did not treat the Atlantic as a single uniform entity. During the Age of Discovery English navigators and mapmakers commonly spoke of the "Great Western Ocean," reflecting orientation from European shores toward westward routes. Similarly, an ethnonymic label — the "Aethiopian Ocean" (from Ancient Ethiopia) — was applied to the southern reaches of the Atlantic on maps into the nineteenth century, illustrating how coastal associations and regional perceptions produced multiple, overlapping names for parts of the same seascape.

Popular language has also produced informal, contrastive names. In English, the northern Atlantic has been colloquially referred to as "the pond" — a deliberately understating metaphor used in cross-Atlantic expressions since at least the mid-seventeenth century and recorded again in nineteenth-century writings. Such usages underscore how everyday speech can compress large geographic features into familiar, culturally resonant terms.

A modern photographic vantage point — the Atlantic as seen from Clare Island, Ireland (1981) — serves as a direct visual anchor for the northern ocean in contemporary geography, linking long-standing toponymic traditions to present-day observational perspectives. Overall, the Atlantic’s toponymy reflects a layered history in which myth, regional perception, navigational practice and colloquial usage have each contributed distinct names and conceptions of the sea.

The geographic limits of the Atlantic are not universally fixed. The International Hydrographic Organization’s 1953 definitions remain a reference but have been revised in places and are not accepted by all authorities, so published extents and the enumeration of oceans and seas vary among sources.

Continental boundaries place the Atlantic between the Americas to the west and Europe and Africa to the east. Its principal surface connection to the Mediterranean Sea is the Strait of Gibraltar; the Mediterranean in turn links to the Black Sea. To the north the Atlantic grades into the Arctic via a chain of seas and straits—notably the Labrador Sea, Denmark Strait, Greenland Sea, Norwegian Sea and Barents Sea—with a conventional northern dividing line passing through Iceland and Svalbard. To the southeast the Atlantic meets the Indian Ocean; a common conventional meridian for that boundary is 20° E running south from Cape Agulhas to Antarctica, although many post‑1953 charts instead truncate the Atlantic at 60° S where the Southern Ocean is delineated.

The Atlantic coastline is markedly indented, pierced by numerous bays, gulfs and marginal seas. Prominent adjacent or subsidiary waters include the Baltic Sea, Black Sea, Caribbean Sea, Davis Strait, Denmark Strait, parts of the Drake Passage, Gulf of Mexico, Labrador Sea, Mediterranean Sea, North Sea, Norwegian Sea and much of the Scotia Sea, among others. Including marginal seas, the Atlantic’s coastline measures 111,866 km (69,510 mi), which is less than the Pacific’s 135,663 km (84,297 mi), indicating substantial but not maximal coastal indentation.

Surface area and volume figures depend on whether marginal seas are counted. With marginal seas included the Atlantic covers about 106,460,000 km2 (41,100,000 sq mi), or 23.5% of global ocean area, and contains approximately 310,410,900 km3 (74,471,500 cu mi), about 23.3% of oceanic volume. Excluding marginal seas reduces the open‑ocean area to roughly 81,760,000 km2 (31,570,000 sq mi) and the volume to about 305,811,900 km3 (73,368,200 cu mi), underscoring the substantial contribution of marginal basins to overall measurements.

The basin is commonly divided into North and South Atlantic components: the North Atlantic covers about 41,490,000 km2 (16,020,000 sq mi), or 11.5% of the global ocean area, and the South Atlantic about 40,270,000 km2 (15,550,000 sq mi), or 11.1%.

Bathymetrically the Atlantic has an average depth near 3,646 m (11,962 ft). Its greatest known depth is the Milwaukee Deep in the Puerto Rico Trench, measured at approximately 8,376 m (27,480 ft), reflecting considerable vertical relief within the basin.

Bathymetric analysis of the Atlantic relies heavily on depth-coded (false‑color) maps that translate measured depths into discrete color bands, providing a visually intuitive means to delineate seafloor morphology—including ridges, abyssal plains and trench systems—and to interpret basin-scale geomorphic patterns. The dominant bathymetric element in the basin is the Mid‑Atlantic Ridge (MAR), a continuous, submarine mountain chain whose axial topography forms the principal structural high of the Atlantic seafloor.

The MAR extends essentially the full meridional length of the basin, from about 87°N (roughly 300 km south of the North Pole) to the subantarctic region near Bouvet Island at ~54°S. Its latitudinal span places the ridge across diverse climatic and oceanographic regimes, so that its relief, segmentation and associated volcanic–tectonic activity exert primary control on the distribution of sediments, the configuration of abyssal plains, and aspects of regional ocean circulation. Recognition of the ridge‑dominated character of Atlantic bathymetry grew from systematic depth‑sounding programmes in the late 19th and early 20th centuries—notably the Challenger and Meteor expeditions—and has been advanced subsequently by institutional mapping and research efforts (for example, Columbia University’s Lamont–Doherty Earth Observatory and the U.S. Navy Hydrographic Office as of 2001). Interpreting the MAR as a long‑lived mid‑ocean ridge system is therefore central to understanding Atlantic tectonics and the principal relief patterns evident on bathymetric charts.

Mid‑Atlantic Ridge

The Mid‑Atlantic Ridge (MAR) is a single, continuous submarine mountain chain that effectively bisects the Atlantic Ocean along its length, organizing a series of basins bounded by transverse ridges and, where it rises above sea level, forming volcanic island groups. Morphologically the ridge stands prominently above the surrounding abyssal plain, commonly 2–3 km higher and frequently exceeding 2,000 m in elevation; in most sectors the ridge crest lies at depths shallower than about 2,700 m, while the relative depth of the ridge base is on the order of three times that of the crest.

Early quantitative mapping of the MAR began with the Challenger expedition in the 1870s, which reported an elevated ridge averaging roughly 1,900 fathoms (≈3,500 m) below the surface. Subsequent echo‑sounding surveys by the German Meteor expedition in the 1920s refined the ridge’s continuity, and intensive investigations in the 1950s supplied the bathymetric and age data that were instrumental in demonstrating seafloor spreading and establishing modern plate‑tectonic theory.

Structurally, the MAR is an axial rift valley and an active divergent plate boundary: it separates the North American and Eurasian plates in the North Atlantic and the South American and African plates in the South Atlantic, and it is a primary locus of lithospheric extension and basaltic magmatism. Magmatic activity produces subaerial basaltic volcanoes on islands (for example Eyjafjallajökull in Iceland) and submarine forms such as pillow lavas on the seafloor.

Although the ridge largely impedes abyssal water exchange between its flanks, major transform and fracture systems interrupt it at key latitudes and enable deep‑water passage—notably the Romanche Trench near the Equator and the Gibbs fracture zone near 53°N. At roughly 40°N the Azores–Gibraltar transform (the Nubian–Eurasian plate boundary) intersects the MAR at the Azores triple junction adjacent to the Azores microplate; a less well‑defined boundary between the North and South American plates meets the ridge near the Fifteen‑Twenty fracture zone at about 16°N.

Where the MAR breaches the sea surface it has generated island environments of high geological, biological and cultural value. Several such islands form part of World Heritage nominations for their geology, and four island areas are recognized for Outstanding Universal Value: Þingvellir (Iceland); the Landscape of the Pico Island Vineyard Culture (Portugal); Gough and Inaccessible Islands (United Kingdom); and Fernando de Noronha and Atol das Rocas Reserves (Brazil).

Ocean floor

The Atlantic seafloor features a mixture of extensive shallow margins and broadly flat deep basins. Continental shelves are conspicuously wide in three primary sectors—off Newfoundland, the southern tip of South America, and northeastern Europe—and the collective shelf and margin systems constitute roughly 11% of the basin’s seabed; comparatively few deep channels dissect the continental rise. In many western Atlantic areas the margin is dominated by carbonate platforms rather than clastic slopes, notable examples being the Blake Plateau and the Bermuda Rise.

Beyond the margins, the deep-floor morphology is dominated by broad abyssal plains interrupted by isolated deeps and trenches, seamounts (including flat-topped guyots), submarine basins and plateaus, and sparse but extensive channelized systems. Between 60°N and 60°S the Atlantic’s mean depth is about 3,730 m, with the most frequently occurring depths (the modal class) between 4,000 and 5,000 m. The Laurentian Abyss is a prominent named basin on the North Atlantic margin.

Most Atlantic margins are tectonically passive; where active margins occur they produce the basin’s greatest depths, for example the Puerto Rico Trench (maximum ~8,376 m) in the western Atlantic and the South Sandwich Trench (maximum ~8,264 m) in the South Atlantic. In the southern basin, two major bathymetric ridges—the Walvis Ridge and the Rio Grande Rise—form topographic barriers that modify regional circulation and constrain water‑mass exchange.

Submarine canyons form dense networks off northeastern North America, western Europe and northwestern Africa; many incise the continental slope, continue across the rise and, in some cases, evolve into deep-sea channel systems across the abyssal plain. Early systematic mapping of these features began to benefit from shipborne sonar: a landmark 1922 survey by the USS Stewart used echo sounding—transmitted acoustic pulses returning echoes from the seabed—to produce continuous bathymetric profiles across the Atlantic.

Water characteristics of the Atlantic are governed by a combination of latitude-dependent heating, large-scale currents, seasonal sea‑ice dynamics, and atmospheric teleconnections. Sea‑surface temperatures reflect the latitudinal distribution of incoming solar radiation and the influence of surface currents and seasonal cycles, spanning values beneath −2 °C to in excess of 30 °C. Warmest surface waters occur in intertropical and subtropical bands, with the coldest confined to polar regions; in midlatitudes the meridional temperature gradient and seasonal forcing produce the largest month‑to‑month contrasts, commonly on the order of 7–8 °C. A conspicuous example of current‑driven temperature change is the Gulf Stream, which transports warm water northeastward from the eastern seaboard of North America toward western Europe and cools by roughly 20 °C along its transatlantic path.

Vertically, the Atlantic circulation comprises linked surface and deep limbs of the thermohaline conveyor, with poleward surface flows balanced by abyssal return currents that redistribute heat and salt between basins. Cartographic representations typically differentiate these branches by color to emphasize their connectivity. At the basin scale the Coriolis force imposes opposite rotational senses on the two hemispheres, producing a clockwise circulation in the North Atlantic and a counter‑clockwise gyre in the South Atlantic; these gyre dynamics determine the trajectories of warm and cold boundary currents.

High‑latitude seasonal ice cover—notably from October through June in marginal seas such as the Labrador Sea, the Denmark Strait and parts of the Baltic—modifies albedo, salinity and air–sea exchanges, with strong local impacts on ocean stratification and heat fluxes. Tidal regimes vary regionally; portions of the southern basin exhibit predominantly semi‑diurnal tides (two highs and two lows per lunar day). Superimposed on these processes, the North Atlantic Oscillation (especially north of ~40°N) alters pressure gradients, storm tracks and surface winds, thereby modulating regional ocean circulation and temperature patterns across the basin.

Salinity

The Atlantic is, on average, the saltiest of the world’s major oceans: open‑ocean surface salinity typically ranges from about 33 to 37 parts per thousand (3.3–3.7% by mass), with seasonally and latitudinally driven variations. Surface salinity is governed chiefly by the balance between evaporation, precipitation, river discharge and sea‑ice melt: enhanced evaporation raises salinity locally, whereas precipitation, freshwater input from rivers and melting ice dilute it.

This balance produces a characteristic spatial pattern. The lowest surface salinities occur just north of the equator—where intense tropical rainfall reduces salt content—and more generally at high latitudes and along continental margins receiving large river outflows. In contrast, maxima are found in the subtropics, near roughly 25°N and 25°S, where relatively low precipitation combined with strong net evaporation concentrates salt and yields the Atlantic’s highest surface values.

Elevated surface salinity in the Atlantic has an important dynamical consequence: by increasing seawater density (especially when paired with surface cooling), high salinity facilitates deep‑water formation and thereby helps sustain the Atlantic meridional overturning circulation. Two principal mechanisms help preserve the basin’s elevated salinity in the face of freshwater inputs. First, the Agulhas leakage system injects salty Indian Ocean waters into the South Atlantic through retroflection and the shedding of warm, saline rings south of Africa, directly boosting South Atlantic salinity. Second, the so‑called Atmospheric Bridge operates when subtropical Atlantic evaporation exports freshwater as vapor to other regions (notably into the Pacific), effectively removing freshwater from the basin and concentrating salt in the subtropical Atlantic. Together these processes underpin the Atlantic’s distinctive salinity distribution and its role in large‑scale ocean circulation.

Water masses

The Atlantic’s vertical hydrographic structure is conventionally divided into three principal layers: upper waters (0–500 m), intermediate waters (500–1,500 m), and deep and abyssal waters (1,500 m to the bottom). Each layer comprises distinct, named water masses defined by characteristic temperature and salinity ranges and by their formation and modification histories.

Upper waters (0–500 m) include four principal masses: Atlantic Subarctic Upper Water (ASUW; T ≈ 0.0–4.0 °C, S ≈ 34.0–35.0), Western North Atlantic Central Water (WNACW; T ≈ 7.0–20 °C, S ≈ 35.0–36.7), Eastern North Atlantic Central Water (ENACW; T ≈ 8.0–18.0 °C, S ≈ 35.2–36.7), and South Atlantic Central Water (SACW; T ≈ 5.0–18.0 °C, S ≈ 34.3–35.8). The northern ASUW is a source for subarctic and North Atlantic intermediate waters through cooling and modification. The central-water regime is zonally differentiated: the western sector is strongly influenced by the Gulf Stream, while the eastern sector is relatively saltier because of proximity to Mediterranean outflow; north–south continuity links North and South Atlantic central waters near ~15°N.

Intermediate waters (500–1,500 m) comprise several subpolar-formed, relatively low-salinity masses and one high-salinity product of evaporation: Western Atlantic Subarctic Intermediate Water (WASIW; T ≈ 3.0–9.0 °C, S ≈ 34.0–35.1), Eastern Atlantic Subarctic Intermediate Water (EASIW; T ≈ 3.0–9.0 °C, S ≈ 34.4–35.3), Mediterranean Water (MW; T ≈ 2.6–11.0 °C, S ≈ 35.0–36.2), and Arctic Intermediate Water (AIW; T ≈ −1.5–3.0 °C, S ≈ 34.7–34.9). AIW advects southward from polar regions and is an important precursor for North Atlantic Deep Water formation south of the Greenland–Scotland sill. The intermediate layer exhibits marked zonal contrasts in salinity that reflect regional formation and subsequent mixing.

The deep and abyssal regime (>1,500 m) is dominated by a small number of bottom and deep waters: North Atlantic Deep Water (NADW; T ≈ 1.5–4.0 °C, S ≈ 34.8–35.0), Antarctic Bottom Water (AABW; T ≈ −0.9–1.7 °C, S ≈ 34.6–34.7), and Arctic Bottom Water (ABW; T ≈ −1.8 to −0.5 °C, S ≈ 34.9). NADW is a composite formed from multiple components: two products of open‑ocean deep convection (classical Labrador Sea water and upper Labrador Sea water) and two dense overflow-derived waters (Denmark Strait overflow and Iceland–Scotland overflow waters originating at the Greenland–Iceland–Scotland sill). These components are progressively modified by mixing with other deep and bottom waters as NADW transits the Atlantic and global oceans.

NADW properties and circulation are further altered by inputs from AABW and Mediterranean overflow, and the overall NADW conveyor is sustained in part by persistent warm shallow inflows into the northern North Atlantic that transport heat poleward and contribute to the relatively mild European climate. The Atlantic’s unusually broad salinity range arises from the asymmetry of the northern subtropical gyre together with multiple source contributions (Labrador Sea, Norwegian–Greenland Sea, Mediterranean overflow, South Atlantic Intermediate Water), producing strong zonal and meridional salinity gradients. Variations in NADW formation have been implicated in past climate shifts; in the modern era anthropogenic tracers (tritium, radiocarbon, CFCs) have been used to map NADW transit times, ventilation pathways, and mixing.

Gyres

The Atlantic basin is structured by two principal subtropical gyres that concentrate warm waters and frame basin‑scale circulation: a clockwise, warm‑water gyre in the North Atlantic and a counter‑clockwise counterpart in the South Atlantic. These large‑scale gyres establish the background for regional current systems and the meridional transport of heat.

In the North Atlantic, surface circulation is controlled chiefly by the Gulf Stream, its offshoot the North Atlantic Current, and the broad Subpolar Front that separates subtropical from subpolar waters. Together these features advect subtropical heat northward, moderating climate in the North Atlantic and over Europe. Within the subpolar gyre, subtropical waters are cooled and mixed to form colder subpolar and polar masses; part of this cooled water returns via the Labrador Sea to rejoin the subtropical circulation, closing a surface loop. The subpolar gyre itself is cyclonic and its circulation is shaped more by currents entering from marginal seas and by regional topography than by direct wind forcing, with signatures evident from sea level to deep layers. The eastern sector contains eddying branches of the North Atlantic Current that carry warm, saline subtropical water into the northeastern Atlantic; winter cooling there drives return flows that converge along Greenland’s eastern continental slope, producing a strong (~40–50 Sv) boundary current around the Labrador Sea margins.

Approximately one third of the transport in these return currents is transformed into the deep limb of North Atlantic Deep Water (NADW), a primary component of the meridional overturning circulation (MOC) that governs northward heat transport and is sensitive to anthropogenic forcing. The subpolar gyre exhibits pronounced decadal to centennial variability linked to the North Atlantic Oscillation; these fluctuations are particularly manifest in Labrador Sea Water and the upper MOC, connecting subpolar dynamics to broader climate variability.

The South Atlantic is dominated by an anticyclonic southern subtropical gyre that supplies South Atlantic Central Water, while Antarctic Intermediate Water forms in the circumpolar sector near the Drake Passage and Falkland region; both water masses receive contributions from the Indian Ocean. Embedded within the subtropical system off southeast Africa is a smaller, cyclonic Angola Gyre. Near‑surface signatures of the southern subtropical gyre are modified by a wind‑driven Ekman layer, which alters surface transport and air–sea exchange. The subtropical gyre’s residence time is estimated at 4.4–8.5 years, and beneath the thermocline the southward flow of NADW continues as part of the global deep circulation that links the Atlantic to the world ocean.

The Sargasso Sea is a biologically distinct sector of the western North Atlantic, delimited not by land but by a ring of major currents—the Gulf Stream, North Atlantic Drift and the North Equatorial Current—that encloses a roughly 4,000 km wide region characterized by the continuous presence of floating brown algae, principally Sargassum fluitans and S. natans. These macroalgae form persistent rafts that define a unique pelagic habitat; genetic and morphological evidence suggests their lineage traces back to Tertiary shorelines of the former Tethys Ocean, with populations maintained through long-term vegetative growth while drifting in open ocean waters.

The floating algal matrix supports a suite of specialised, often endemic organisms adapted to life among the rafts. A conspicuous example is the sargassum fish, a predator whose algal-like appendages permit cryptic hovering within the mats to ambush prey. Paleontological data reinforce the antiquity of this biotic association: fossils of fish with morphologies akin to modern Sargassum associates have been retrieved from fossilized Tethyan bays in the Carpathian region, implying continuity of these lineages from coastal Tethyan systems into the open-ocean Sargasso community. Mid-20th century palaeontological work described a "quasi‑Sargasso assemblage" that appears to have originated in the Carpathian Basin and dispersed across Sicily into the central Atlantic, consistent with a scenario in which Tethyan elements migrated into the Atlantic basin as the seaway closed at the end of the Miocene (circa 17 Ma) and subsequently evolved into the modern Sargasso fauna.

The southern Sargasso Sea is also the principal spawning area for both the European and American eels, a discovery historically attributed to early 19th‑century research. After hatching, eel larvae (leptocephali) are transported by prevailing ocean currents—notably the Gulf Stream—toward continental feeding grounds in North America, Europe and northern Africa, a process crucial for their life cycle. Adult eels undertake extensive return migrations from these feeding areas to the Sargasso spawning grounds, with European eels travelling distances in excess of 5,000 km and American eels around 2,000 km. Recent, still contested studies suggest that both larvae and adults may employ geomagnetic cues during their oceanic movements, implying a potential role for Earth's magnetic field in long‑distance navigation.

Climate (Atlantic Ocean)

The Atlantic exerts a dominant influence on adjacent regional climates through its large heat capacity, surface-temperature patterns, and circulation. Because seawater warms and cools far more slowly than land, the ocean’s thermal inertia produces maritime climates characterized by reduced seasonal temperature ranges and generally milder conditions near coasts than in continental interiors.

Sea-surface temperature (SST), ocean currents and prevailing winds together control the distribution of heat and moisture. Currents transport significant heat meridionally — most notably the Gulf Stream and its northeastward continuation, the North Atlantic Drift — moderating winter temperatures along the southeastern coast of North America, tempering extremes on the Florida Peninsula, and importing heat into the atmosphere above northwestern Europe so that the British Isles experience comparatively mild, cloudy winters for their latitude. Conversely, cold currents promote features such as frequent, dense fog where they encounter warm, humid air masses (e.g., the Grand Banks off eastern Canada and the northwest African coast).

The ocean is the principal source of atmospheric moisture through evaporation, so coastal and near-coastal precipitation regimes are closely linked to oceanic evaporation rates and the pathways of winds that advect that moisture inland. Trade-wind convergence zones in the Atlantic — migrating belts where the trade winds meet along prevailing tracks — introduce atmospheric instability; when sea-surface temperatures and vertical wind-shear conditions are favorable, these convergence zones can organize and intensify into tropical cyclones (hurricanes).

Climatic patterns in the Atlantic are also strongly organized by latitude: the warmest oceanic belt lies north of the equator in the tropical and subtropical Atlantic, while the coldest oceanic climates occupy high latitudes and are associated with seasonal or permanent sea-ice cover. Ultimately, the coupled effects of SST, oceanic heat transport, evaporation and atmospheric circulation determine the characteristic thermal and precipitation regimes of coastal and adjacent inland regions.

Natural hazards

The Atlantic Ocean presents a range of seasonal and spatially variable natural hazards that affect maritime and coastal activities. Ice hazards occur in both hemispheres: notable southern-hemisphere examples such as iceberg A22A demonstrate that large bergs are not confined to the North Atlantic, while in the north iceberg danger is concentrated along the shipping approaches to the Grand Banks of Newfoundland. The principal North Atlantic ice season, from early February through late July, coincides with dense transatlantic and coastal traffic, so collision risk is greatest where iceberg presence and shipping density overlap; although higher-latitude polar regions sustain longer ice seasons, their relatively limited commercial traffic reduces the overall exposure there.

Atmospheric hazards are similarly regionally distinct. The persistent Icelandic Low dominates North Atlantic winter climatology and engenders frequent, vigorous storms and strong winds during that season. Tropical cyclones impose a marked summer–autumn hazard in the western North Atlantic, driven by warm sea-surface temperatures and favorable atmospheric conditions; by contrast, tropical cyclones are rare in the South Atlantic, where persistent vertical wind shear and a weak Intertropical Convergence Zone generally inhibit cyclogenesis and intensification.

Geology and plate tectonics

The Atlantic basin is underlain by typical oceanic lithosphere composed predominantly of dense mafic rocks—basalt at the seafloor and gabbro at depth—over which a locally thin veneer of pelagic and hemipelagic sediments (clays, silts and siliceous oozes) accumulates on the abyssal plains. In contrast, the continental margins that bound the ocean are built of thicker, lower‑density felsic crust (shelf, slope and adjacent continental crust) that is substantially older than the neighbouring oceanic plate, producing a sharp contrast in composition, thickness and age across the margin.

Preserved Atlantic oceanic crust attains maximum ages of roughly 145 million years; these oldest remnants occur along the basin flanks, notably off West Africa and the eastern seaboard of North America, with correlative aged crust on both sides of the South Atlantic. Along the continental shelves and slopes, sedimentary sequences can be thick and complex, recording variations in provenance and depositional regime driven by climatic change, ocean circulation and tectonic evolution.

Sediment character on the margins is strongly facies‑controlled. Warm, shallow carbonate platforms dominate parts of the North American margin (for example Florida and the Bahamas), where biological carbonate production produces extensive carbonate accumulations. By contrast, shallow shelves receiving significant riverine input are siliciclastic‑dominated; Georges Bank typifies such settings, with coarse fluvial sands and silts reworked by shelf processes. Finally, Pleistocene glaciation delivered coarse clastic material—coarse sands, gravels and erratics—onto shelves and slopes off Atlantic Canada, producing conspicuous deposits off Nova Scotia and within the Gulf of Maine that reflect ice‑sheet and glaciofluvial dynamics.

The central Atlantic region records the earliest stages of Pangaea’s fragmentation, when rift basins developed between what are now eastern North America and northwest Africa during the Late Triassic–Early Jurassic. This rifting—whose onset is variously dated between ca. 200 and 170 Ma—was accompanied by uplift that contributed to the nascent Atlas orogeny. The continental separation and initial seafloor formation were synchronous with emplacement of the Central Atlantic Magmatic Province (CAMP), an exceptionally large igneous event temporally linked to the Triassic–Jurassic biotic crisis. CAMP produced extensive tholeiitic intrusions and effusive flows (dikes, sills and lavas) around 200 Ma; occurrences are preserved across eastern North America, West Africa and northern South America, with quantitative estimates of CAMP-covered area near 4.5 × 10^6 km^2 overall and roughly 2.5 × 10^6 km^2 occupying parts of present-day northern and central Brazil.

Much later, tectonic closure of the Central American Seaway at the end of the Pliocene (≈2.8 Ma) converted an oceanic corridor into the Panamanian isthmus, with major biogeographic and oceanographic consequences. Terrestrially, the new land connection precipitated the Great American Interchange, a widespread exchange and associated turnover of mammalian and other faunas. Oceanographically, cessation of throughflow reconfigured surface currents, salinity distributions and sea-surface temperatures between the Atlantic and Pacific—a reorganization sometimes termed the “Great American Schism.” The isthmus also established a persistent marine barrier, isolating Atlantic and Pacific marine assemblages and driving divergent evolutionary trajectories (speciation for some lineages, extinction for others), thereby reshaping regional marine biodiversity.

North Atlantic — concise summary

The North Atlantic Basin is bounded to the south by the conjugate continental margins of Newfoundland and Iberia and to the north by the Arctic Eurasian Basin. Its opening proceeded from the central Atlantic in a multi‑stage sequence that closely followed the former margins of the Iapetus Ocean; reconstructions describe six outward propagating spreading stages (including Iberia–Newfoundland, Porcupine–North America, Eurasia–Greenland and Eurasia–North America). The regional pattern of active and inactive spreading systems reflects the imprint of the Iceland mantle plume on the evolving Mid‑Atlantic Ridge.

Seafloor spreading produced pervasive crustal extension along continental margins, generating rift valleys, troughs and sedimentary basins. The Rockall Trough exemplifies this process, opening between about 105 and 84 Ma; elsewhere rifts propagated but failed (for example toward the Bay of Biscay), leaving asymmetric margin architectures and sedimentary depocentres.

The Labrador Sea records a later episode of oceanic spreading, initiated at roughly 61 Ma and persisting until ~36 Ma. Magmatism there comprises two main pulses: an earlier phase (≈62–58 Ma) that predates Greenland’s separation from northern Europe, and a subsequent phase (≈56–52 Ma) synchronous with that separation. These pulses are part of a broader Paleogene magmatic event linked to plume activity.

Iceland represents the locus of a concentrated mantle plume that began producing voluminous volcanism around 62 Ma. The plume generated extensive basaltic outpourings that formed flood basalts and lava fields preserved on Baffin Island, Greenland, the Faroe Islands and Scotland; widespread distal ash layers reached Western Europe and provide useful stratigraphic markers for this interval.

Rifting and plume‑related magmatism produced sustained coastal uplift and crustal exhumation along North Atlantic margins. In East Greenland, Gunnbjørn Fjeld attains high elevation despite being capped by several kilometres of basalt, and uplift has exposed older Mesozoic sediments beneath the lava pile — a relationship paralleled by uplifted lava fields and underlying sedimentary sequences in the Hebrides.

Seamounts are concentrated along the Mid‑Atlantic Ridge: the North Atlantic contains about 810 seamounts overall, and the OSPAR inventory records 104 features in the northeast Atlantic region, of which 74 lie within national exclusive economic zones and 46 occur near the Iberian Peninsula. The Mid‑Atlantic Ridge, where it intersects plume material from Iceland, experiences spatially variable magmatic supply; this produces alternating volcanically productive (active) and low‑flux or relic (inactive) ridge segments, with corresponding effects on seafloor morphology, seamount formation and margin uplift.

Taken together, the sequence from the Early Cretaceous Rockall Trough opening (≈105–84 Ma), through the Paleogene magmatic pulses (≈62–58 Ma and 56–52 Ma) and the Labrador Sea spreading episode (≈61–36 Ma), demonstrates how episodic rifting and plume‑driven magmatism governed continental breakup, redistributed volcanic and sedimentary deposits across Baffin Island, Greenland, the Faroes and Scotland, and produced persistent stratigraphic and topographic contrasts along North Atlantic margins.

South Atlantic

The South Atlantic formed during the Early Cretaceous as West Gondwana fragmented, producing the conjugate margins of present-day South America and Africa. Early cartographic recognition of the complementary coastlines culminated in the first computer-assisted plate reconstructions in 1965, but subsequent work has shown that shoreline fits alone are insufficient; intra-continental rifts and distributed deformation zones are required to accommodate a northward-propagating rift system and the subdivision of the continental plates into smaller sub-plates.

Tectonically and geographically the basin is commonly divided into four segments that record different timing and styles of break-up: the equatorial segment (from ~10°N to the Romanche fracture zone, RFZ), the central segment (RFZ to the Florianopolis fracture zone, FFZ, north of Walvis Ridge and the Rio Grande Rise), the southern segment (FFZ to the Agulhas–Falkland fracture zone, AFFZ), and the Falkland segment (south of the AFFZ). These segments preserve distinct rift histories and seafloor-spreading trajectories.

The southern segment documents intense Early Cretaceous plume-related magmatism associated with the Paraná–Etendeka Large Igneous Province and Tristan hotspot. Major eruptive and intrusive activity at ~133–130 Ma produced an estimated 1.5–2.0 × 10^6 km^3 of magma, covering some 1.2–1.6 × 10^6 km^2 onshore across Brazil, Paraguay and Uruguay and tens of thousands of square kilometres on the African margin. Extensive dyke swarms in Brazil, Angola, eastern Paraguay and Namibia, together with offshore basalt flows reaching as far south as the Falklands and South Africa, indicate a much wider magmatic footprint and record failed rift systems. Magmatism in both onshore and offshore basins of the central and southern segments spans broadly 147–49 Ma, with principal volumetric pulses between ~143–121 Ma and ~90–60 Ma.

Rift kinematics in the Falkland segment began earlier, with right-lateral (dextral) motion between Patagonia and the Colorado sub-plates from the Early Jurassic (~190 Ma) through the Early Cretaceous (to ~126.7 Ma). By ~150 Ma seafloor spreading had propagated northward into the southern segment, and by ~130 Ma rifting reached the conjugate Walvis Ridge–Rio Grande Rise plateaus. In the central segment rift propagation ultimately led to internal continental breakup in Africa and the opening of the Benue Trough at ~118 Ma; accurate magnetic dating here is hindered by the Cretaceous Normal Superchron, a ~40 Myr interval of prolonged polarity stability. The equatorial segment represents the terminal stage of South Atlantic opening; emplacement of seafloor spreading and establishment of the Equatorial Atlantic Gateway likely occurred between ~120 and 96 Ma, but geomagnetic-anomaly dating is problematic across the Equator.

A later plate-motion reorganization between South America and Antarctica beginning around 50 Ma initiated opening of the Drake Passage. Early Middle Eocene development of small basins and a shallow gateway was followed between ~34 and 30 Ma by a deeper seaway. This progressive deepening contributed to Eocene–Oligocene cooling and the initiation and growth of the Antarctic ice sheet, linking South Atlantic and southern-ocean tectonics to major Cenozoic climatic change.

Closure of the Atlantic

Recent tectonic observations indicate the incipient development of a subduction margin immediately west of Gibraltar, at the transition between the western Mediterranean and the central Atlantic. Here, oceanic or strongly thinned continental lithosphere shows the first signs of descent beneath an overriding plate, marking the earliest stage of a convergent boundary in the eastern Atlantic. This nascent system is driven by westward migration of the Gibraltar Arc—a curved orogenic belt at the western Mediterranean margin—whose propagation couples local deformation to the broader Africa–Eurasia convergence and focuses shortening offshore of Iberia and northwest Africa.

The combined action of arc migration, sustained plate convergence, and pre-existing lithospheric heterogeneities is expected to guide the subduction system’s maturation through a recognizable sequence: trench initiation, slab sinking, development of an accretionary prism and forearc, and eventual establishment of a mature subduction margin. These processes reflect a progressive change from passive-margin or intraplate shortening to active, trench-forming convergent tectonics in the eastern Atlantic domain.

Comparable but independently advancing subduction systems exist in the western Atlantic sector: the Scotia Arc south of South America and elements of the Caribbean plate system both exhibit eastward-propagating trench migration and lithospheric consumption. Viewed together with the Gibraltar-related initiation, these eastward- and westward-propagating convergent zones constitute a distributed network of active subduction propagation around the Atlantic margins.

At a geodynamic scale, the near-simultaneous initiation and propagation of these margins may presage the long-term narrowing of the Atlantic basin. In terms of the Wilson cycle, these developments mark a transition away from a spreading-dominated, steady-state ocean toward a contractional phase characterized by new trench formation and plate convergence—an incipient stage of Atlantic closure.

Old-World coastal prehistory is characterized by an early African demographic expansion and a progressive intensification of marine-oriented lifeways. Mitochondrial DNA points to a major population growth within Africa between ca. 80–60 ka from a single small source; this pulse, occurring amid the behavioral and environmental fluctuations of Marine Isotope Stages 5–4, set the stage for a dispersal out of Africa by ~65 ka that rapidly carried anatomically modern humans into Asia, Europe and Australasia and largely supplanted local archaic populations.

Archaeological traces attest to early coastal use in Africa and its role in outward dispersal. Deeply stratified Middle Stone Age shell middens at Ysterfontein (western South Africa; ~50 ka) and the roughly contemporary sequence at Enkapune Ya Muto (Kenya; ~50–45 ka) document small, dispersed forager groups exploiting littoral resources. In these early contexts rates of reproduction and intensity of resource extraction appear lower than in later periods, suggesting modest, opportunistic coastal economies rather than densely settled maritime adaptations.

From the Late Pleistocene into the Holocene there is clear evidence for a marked amplification of marine resource exploitation and associated technologies. Cave and shell-midden sequences in Europe (for example La Riera, Asturias; 23–13 ka) show increasing shell deposition through time, and by the early Holocene many middens in Portugal, Denmark and Brazil contained vast volumes of shell and artefactual debris. The Ertebølle complexes in Denmark exemplify this escalation: over roughly a millennium they accumulated on the order of 2,000 m3 of shell—tens of millions of molluscs—reflecting dense coastal occupation and heavy reliance on marine foods. Concomitant innovations—boats, harpoons, fish‑hooks—appear with these larger-scale economies, marking a shift from intermittent littoral foraging to more systematic maritime technologies and settlements.

Palaeogeographic and climatic events repeatedly restructured Atlantic coastal settlement. During the Last Glacial Maximum (~20 ka) people withdrew from exposed North Atlantic coasts into Mediterranean refugia; subsequent climatic amelioration promoted recolonization by Magdalenian-associated groups and later Mesolithic foragers, but this process was episodically disrupted by volcanic eruptions (e.g., Laacher See), the inundation of Doggerland and the formation of the Baltic basin. Many European Atlantic coasts therefore achieved permanent, dense occupation only after these transformations, around 9–8.5 ka.

Preservation and visibility biases shape the archaeological record: substantial early coastal foraging occurred on now-submerged continental shelves, so many excavated sites lie kilometers inland from former shorelines and lower archaeological levels in caves commonly contain fewer shells because shell debris was sometimes transported inland. Although Late Stone Age shell-midden patterns resembling MSA littoral use are found on every inhabited continent, the Holocene is distinguished by markedly greater scale, density and complexity of artefact assemblages—reflecting higher population densities, improved technologies and more sedentary coastal settlement patterns.

New World

During the Last Glacial Maximum the Laurentide Ice Sheet dominated northern North America while Beringia formed a terrestrial bridge between Siberia and Alaska, a geographic configuration that long framed hypotheses of human entry to the Americas. Classic models that guided twentieth‑century debate included Paul S. Martin's "blitzkrieg" scenario, which posited a rapid, single‑pulse Clovis expansion through an ice‑free corridor about 13,000 years ago, and the competing "three‑wave" model of successive migrations across the Bering Land Bridge. For decades these two frameworks shaped interpretations of New World peopling.

Recent archaeological discoveries and spatial patterns of early sites have undermined the simplicity of those models. Some of the oldest reliably dated sites are in South America rather than along a north‑to‑south interior corridor; evidence from northeast Siberia indicates minimal human presence during the LGM; and Clovis assemblages are disproportionately concentrated in eastern North America near the Atlantic seaboard rather than exclusively along an interior corridor. Parallel molecular studies using mitochondrial, Y‑chromosome and ancient/autosomal DNA have produced ambiguous and sometimes conflicting signals that do not unambiguously corroborate either the blitzkrieg or three‑wave scenarios. Because material and genetic datasets presently diverge in important respects, current scholarly expectation favors the development of integrated, multidisciplinary hypotheses—rooted in additional archaeological discovery, improved chronologies and expanded ancient DNA sampling—to reconcile these lines of evidence.

To account for early South American sites and observed site distributions, researchers have advanced alternative dispersal routes. Coastal models propose rapid trans‑Pacific movement or island‑hopping directly to the western coasts of South America; high‑latitude proposals posit entry via the Canadian Arctic followed by down‑coast movement along the North American Atlantic margin. Atlantic‑crossing alternatives (for example, the Solutrean hypothesis and other pre‑Columbian contact ideas) have also been suggested but remain largely speculative or contested within the scholarly community.

Medieval Norse sources and maps indicate only fragmentary knowledge of trans‑Atlantic geography. Norse expansion across the North Atlantic led to the colonization of the Faroes and Iceland in the ninth and tenth centuries and to the establishment of settlements in Greenland before 1000 CE; regular contact with Greenland ceased in 1409 and the Norse presence there was abandoned during the early Little Ice Age. Multiple interacting causes explain the Greenland Norse collapse: an agrarian economy vulnerable to soil loss and erosion, limited adoption of indigenous Arctic subsistence strategies, climatic deterioration producing food shortages, and a decline in external support and trade exacerbated by demographic shocks such as the Black Death. Iceland itself was settled between ca. 865 and 930 CE during a regional warm interval—winter temperatures reconstructed near 2 °C—conditions that initially permitted high‑latitude farming. Rapid climatic decline thereafter produced severe famines documented in contemporary sources, and by the early thirteenth century Icelandic agriculture had shifted toward cultivation of short‑season crops (e.g., barley) and away from extensive hay production.

Atlantic World

The circulation of the Atlantic gyres — large, wind- and current-driven systems — fundamentally structured early long-distance navigation by creating reliable outbound and return corridors. Portuguese mariners in particular exploited these predictable wind-current circuits for the Carreira da Índia, and the same dynamics steered seminal voyages that reconfigured global geography: Columbus’s 1492 crossing to the Americas, Vasco da Gama’s 1498 rounding of the Cape of Good Hope to reach India, and Pedro Álvares Cabral’s 1500 landfall in Brazil after being carried by the South Atlantic Gyre. These navigational regularities also made trans-Atlantic shipping routinized and slow-moving, which in turn facilitated interception by privateers and pirates acting against Iberian treasure convoys.

Spain and Portugal converted maritime discoveries into extensive colonial empires in the Americas, extracting precious metals and imposing coerced indigenous labor systems. To secure and monopolize these new sources of wealth, Iberian crowns sought to exclude other European competitors, a policy that provoked armed rivalry and eventually led to papal-mediated partitioning of newly claimed territories between Spain and Portugal. Excluded powers — notably England, France, and the Dutch Republic — increasingly turned to privateering and opportunistic alliances with pirates as a means of accessing colonial riches.

The demographic and labor consequences in the Americas were profound. Epidemics, violence, and forced labor produced catastrophic declines in indigenous populations; colonial elites substituted African slave labor to sustain plantation and mining economies. Documented trans-Atlantic slave voyages span from the early 16th century into the mid-19th century (records commonly summarized for 1525–1863), and between the 15th century and 1888 an estimated 9.5 million Africans were transported to the New World, the majority to agricultural labor. Brazil was the last American polity to cease the slave trade (1888). Legal measures began to restrict the traffic in 1808 (British Empire and the United States banned the trans-Atlantic slave trade), with slavery itself abolished later in the British Empire (1838) and in the United States only after the Civil War (1865).

Economically, the Atlantic system became the foundation of sustained growth for seafaring Western European states from the age of discovery through the Industrial Revolution. Between 1500 and 1800, countries with direct Atlantic access (Britain, France, the Netherlands, Portugal, and Spain) experienced faster growth than much of Eastern Europe and many parts of Asia; by the late 17th century trans-Atlantic commerce had overtaken traditional Mediterranean trade in volume. The distribution of gains was shaped by domestic institutions: merchant classes and commercial interests advanced more rapidly in states with restrained royal authority (notably Britain and the Netherlands), whereas absolutist polities (Portugal, Spain, and France) tended to concentrate profits in the hands of monarchs and their patrons, constraining broader commercial dynamism.

These structural shifts are visible in measurable social and economic indicators. Urbanization in Atlantic-facing European countries rose markedly — from about 8% in 1300 to 10.1% in 1500 and to 24.5% by 1850 — while other European regions moved from roughly 10% to 11.4% to 17% over the same intervals. Likewise, GDP in Atlantic countries approximately doubled over the early modern period compared with an increase of roughly 30% in the rest of Europe, reflecting the centrality of trans-Atlantic trade, colonial extraction, and slave-based plantation agriculture to the rise of Western European maritime powers.

Economy

The Atlantic has been a principal driver of economic development for its littoral states by furnishing the principal transatlantic transport and communication corridors that underpin trade, population movements and the exchange of information, thereby integrating regional economies across its basin. Much of the ocean’s economic value is concentrated along continental margins, where sedimentary basins host significant hydrocarbon accumulations—numerous petroleum and gas fields occur on and beneath continental shelves and rims and have supported large-scale extraction industries.

Biological productivity and living resources constitute another major component of Atlantic wealth. Extensive fish stocks and populations of marine mammals (historically seals and whales) have sustained commercial fisheries, local subsistence activities and associated coastal livelihoods. The nearshore and seabed environment also yields a range of non‑fuel minerals—sand and gravel for construction, placer deposits, polymetallic nodules and various gemstones—each occurring in distinct depositional settings and posing different extraction challenges. High‑value mineralization, including occurrences of gold on the ocean floor at depths of roughly one to two miles and often embedded in rock, would require large, technically complex mining operations; at present many deep‑sea targets remain economically marginal because of the engineering difficulties and recovery costs involved.

These resource potentials coexist with substantial environmental and governance constraints. Oil spills, accumulation of marine debris and at‑sea disposal or incineration of toxic wastes threaten marine and coastal ecosystems, prompting a body of international agreements and regulatory measures aimed at pollution control and environmental protection. Consequently, the Atlantic’s economic geography is defined by the juxtaposition of abundant and diverse resource endowments concentrated on continental shelves and in the deep ocean, and the practical limits on their exploitation—technical feasibility, commercial viability and international legal and environmental frameworks that regulate use and mitigate harm.

Fisheries

The broad continental shelves and offshore banks of the Atlantic rank among the planet’s most productive fishing grounds. Features such as the Grand Banks, Scotian Shelf, Georges Bank, the Bahama Banks, the waters around Iceland, the Irish Sea, Bay of Fundy, Dogger Bank and the Falkland Banks concentrate nutrients, benthic habitat and upwelling, historically supporting very large pelagic and demersal catches.

The UN FAO divides the Atlantic into six major fishing areas (Northeast, Northwest, Eastern Central, Western Central, Southeast and Southwest Atlantic) and identifies three broad temporal patterns in global fisheries since the 1950s: regions with fluctuating but roughly stable catches, regions showing long-term declines after historical peaks, and regions with sustained increases (the latter not observed in the Atlantic but in the Indian Ocean and western Pacific). This spatial variability reflects differences in fishing pressure, fleet history and management.

The Northeast Atlantic, delimited by specific meridians and parallels extending to the pole and subdivided into numerous FAO subareas (e.g., Barents Sea, North Sea, Iceland/Faroes grounds, Rockall, Bay of Biscay, Portuguese waters, Azores and East Greenland), has seen overall declines from the mid-1970s into the 1990s, producing 8.7 million tonnes in 2013. Species dynamics are heterogeneous: blue whiting underwent a pronounced boom–bust (peaking at c. 2.4 million tonnes in 2004, dropping to c. 0.63 million tonnes by 2013), while targeted recovery measures for cod, sole and plaice have reduced mortality and Arctic cod has recovered after mid‑20th century lows. Assessment status is mixed: some stocks (Arctic saithe, haddock) are fished at capacity, sand eel is overfished, capelin has recovered to full exploitation, and several deep-water and redfish taxa remain data-poor and consequently vulnerable; overall about 21% of Northeast stocks are judged overfished. The region accounted for nearly three-quarters (72.8%) of EU catches in 2020, with Denmark, France, the Netherlands and Spain dominant and herring, mackerel and sprats the most frequently landed species.

The Northwest Atlantic experienced a marked decline in landings from roughly 4.2 million tonnes in the early 1970s to 1.9 million tonnes by 2013. Some demersal stocks—Greenland halibut, yellowtail flounder, Atlantic halibut, haddock and spiny dogfish—show weak signs of recovery in the 21st century, whereas emblematic stocks such as Atlantic cod, witch flounder and several redfish populations have not rebounded. Invertebrates, by contrast, have in many cases reached record abundances. Approximately 31% of northwest stocks are overfished. The region’s exploitation history is long and intense: five centuries of cod harvesting off Newfoundland (beginning with early European voyages such as Cabot’s in 1497) yielded on the order of 200 million tonnes; the post‑1950s expansion of distant‑water fleets and technological intensification drove overfishing from the 1960s, prompting regulatory responses only in the late 1970s and culminating in the dramatic early‑1990s collapse of the northwest cod fishery and concurrent declines among many deep‑sea species.

In the Eastern Central Atlantic small pelagics dominate landings (around half of total catches), with sardine production typically between 0.6 and 1.0 million tonnes per year. Total catches have fluctuated since the 1970s, reaching c. 3.9 million tonnes in 2013. Assessments indicate many pelagic stocks are fully exploited or overfished—almost half of stocks in the area are exploited at biologically unsustainable levels—although localized exceptions exist (e.g., some sardine stocks south of Cape Bojador).

Western Central Atlantic catches have fallen since 2000 to about 1.3 million tonnes in 2013. Historically dominated by Gulf menhaden (peaking near 1 million tonnes in the mid‑1980s and about 0.5 million tonnes by 2013), the region now shows widespread stock pressure: round sardinella and several reef species (groupers, snappers) are overfished, and commercially important invertebrates (northern brown shrimp, American cupped oyster) are at or nearing overfished status. Overall, roughly 44% of stocks in the western central Atlantic are being exploited unsustainably.

The Southeast Atlantic saw catches fall from about 3.3 million tonnes in the early 1970s to 1.3 million tonnes in 2013. Horse mackerel and hake together make up nearly half of regional landings. Management reforms enacted from 2006 onwards have helped recovery of deep‑water and shallow‑water hake off South Africa and Namibia, and southern African pilchard and anchovy improved to full exploitation status by 2013.

In the Southwest Atlantic production peaked in the mid‑1980s and subsequently oscillated between c. 1.7 and 2.6 million tonnes. Argentine shortfin squid remains the single most important species but produced only about 0.5 million tonnes in 2013 (roughly half its peak) and is judged fully to overfished; Brazilian sardinella (c. 0.1 million tonnes in 2013) is overfished. Approximately half of stocks in this area are exploited at unsustainable levels, with notable concerns including Cunene horse mackerel (overfished), Whitehead’s round herring (not fully exploited), and persistent overexploitation of perlemoen abalone due to illegal fishing.

Across the basin a recurring theme is poor data coverage for deep‑water and many redfish‑type taxa, increasing both their assessed uncertainty and vulnerability to overexploitation. The patchwork of oscillation, decline and localized recovery observed across Atlantic fishing areas underscores that historical fleet expansion, variable governance and the implementation of regionally specific management measures (e.g., recovery plans, post‑2006 southern African regulations) have been decisive in determining contemporary stock status.

Endangered species

The Atlantic hosts a suite of endangered marine megafauna and medium-sized taxa—notably manatees, pinnipeds (seals and sea lions), sea turtles and whales—that occupy a broad array of coastal, estuarine, freshwater and open-ocean habitats. Their differing habitat affinities and life histories, from tropical manatee seagrass beds to polar haul-out and pack-ice sites used by many seals and some whales, and the long-distance migratory corridors traversed by sea turtles and baleen/odontocete whales, make their conservation an inherently multi-ecosystem and transboundary problem.

Manatees (Sirenia) are obligate herbivores restricted to coastal, estuarine and freshwater systems in tropical and subtropical regions. Their narrow habitat requirements, slow reproductive rates and dependence on seagrass and other aquatic vegetation render local populations highly sensitive to habitat loss, coastal development, boat strikes and incidental capture. Pinnipeds concentrate seasonally at discrete haul-out and breeding sites along productive continental shelves in temperate to polar zones; they are therefore vulnerable to entanglement in fishing gear, disturbance at colonies, and prey shortages linked to overfishing and climate-driven changes in productivity.

Many sea turtle and whale species undertake transoceanic migrations between separate nesting, pupping and feeding areas, exposing them to cumulative threats across multiple jurisdictions. Bycatch in diverse fisheries, collisions with vessels in congested shipping lanes, and degradation of critical coastal habitats all contribute to population declines that reflect pressures distributed through oceanic corridors rather than isolated local causes.

Large-scale drift-net fisheries exemplify a pervasive threat because of their high non-selectivity: drifting near-surface or midwater nets generate substantial bycatch of dolphins and a wide range of seabirds (including albatrosses, petrels and auks), thereby removing both mammalian and avian predators. Such incidental mortality undermines ecosystem structure, reduces recruitment and survival in exploited fish stocks, and can accelerate stock declines by disrupting trophic relationships in addition to direct removals.

These ecological impacts have clear socio-political consequences. Cross-boundary bycatch and consequent depletion of shared resources intensify competition between coastal states and distant-water fleets, complicate management within EEZs and on the high seas, and place additional burdens on regional fisheries management organizations and conservation agreements that must reconcile ecological sustainability with economic interests.

As of December 2020, the treatment of these issues in the Atlantic requires expansion and updating. Robust, spatially explicit analyses of mortality rates, species-specific population trajectories, and jurisdictional case studies are needed to quantify impacts and to guide transboundary conservation measures and fisheries policy.

Waste and pollution

Marine pollution encompasses the introduction of harmful substances—chemical contaminants, organic wastes, and particulate litter—into oceanic waters from both land‑ and sea‑based activities, with consequences for water quality, marine ecosystems, and coastal environments. Fluvial systems are the principal conduits for many of these inputs: rivers transport agricultural nutrients (notably fertilizer-derived nitrogen and phosphorus) and organic effluents from livestock and human settlements into the sea. The consequent enrichment and oxygen consumption can produce hypoxic conditions; where dissolved oxygen falls below levels required by most fauna, so‑called “dead zones” may form.

Solid waste originating from human activity persists as marine debris, which is redistributed by ocean currents and tends to accumulate within subtropical gyres and along shorelines. The North Atlantic has a large accumulation zone—commonly referred to as a garbage patch—that extends on the order of hundreds of kilometres, illustrating the capacity of gyre circulation to concentrate floating litter. Long‑distance transport also results in substantial deposition on remote shores; for example, beaches on isolated islands such as Inaccessible Island in the South Atlantic are extensively strewn with debris despite their remoteness.

Regional patterns of pollution reflect differing sources and uses of the ocean margins. Agricultural runoff and municipal waste are major concerns throughout Atlantic catchments, with notable concentrations of municipal pollution off the eastern United States, southern Brazil, and eastern Argentina. Hydrocarbon contamination from extraction, transport and shipping is a principal problem in several basins, including the Caribbean Sea, the Gulf of Mexico, Lake Maracaibo, the Mediterranean Sea, and the North Sea. Industrial discharges and untreated or poorly treated municipal sewage impose significant pressures on semi‑enclosed and heavily urbanized seas such as the Baltic, the North Sea, and the Mediterranean.

Beyond chronic pollution, singular anthropogenic hazards have also affected the Atlantic. A documented Cold War‑era incident involved a USAF C‑124 aircraft that, after a power failure while carrying nuclear ordnance, jettisoned two nuclear bombs over the ocean; those devices were not recovered, underscoring the potential for long‑lived and hazardous material loss to the marine environment.

Climate change

Recent decades have seen an increase in North Atlantic hurricane activity closely associated with warming of tropical sea‑surface temperatures (SSTs). Two competing attribution hypotheses have been advanced: a natural, multidecadal Atlantic Multidecadal Oscillation (AMO) versus externally forced (anthropogenic) climate change. Multiple lines of observational and statistical evidence increasingly favor a dominant role for human forcing.

Large‑scale changes in ocean circulation have been documented. A 2005 assessment reported a roughly 30% slowdown of the Atlantic Meridional Overturning Circulation (AMOC) between 1957 and 2004; more recent work (2024) finds a further significant weakening of about 12% over the past two decades (as of 2024). This observed decline in AMOC is not consistent with the AMO hypothesis for recent tropical SST trends, because an AMO‑driven SST increase would be expected to coincide with a strengthened, not weakened, AMOC. In addition, analyses of yearly tropical cyclone records fail to reveal the multidecadal periodicity that a purely AMO‑driven mechanism would imprint, further supporting an anthropogenic explanation for the recent SST and hurricane changes.

The ocean’s vertical structure governs the temporal response of the climate system. The upper mixed layer controls heat storage on seasonal to decadal timescales, whereas the deep ocean beneath it has roughly fifty times the heat capacity of the mixed layer and responds on millennial timescales, imparting substantial thermal inertia. Ongoing uptake of heat by the ocean therefore produces a pronounced time lag between radiative forcing and full climate response and drives thermal expansion of seawater—a principal contributor to observed and future sea‑level rise.

Projections indicate that twenty‑first‑century global warming will likely lead to an equilibrium sea‑level rise several times larger than current levels (estimates indicate an eventual rise on the order of five times present values) as ocean heat uptake and long‑term adjustments equilibrate. While glacier mass loss—including potential contributions from the Greenland ice sheet—is assessed to have negligible measurable effect on global sea level within the 21st century in the scenarios considered here, sustained melting over centuries to millennia could yield orders‑of‑magnitude larger consequences: a multi‑century to millennial sea‑level rise on the order of 3–6 m if current melting trajectories continue.