The Atlantic Ocean, the world’s second-largest ocean basin, supports a vast array of marine life and influences global climate. Stretching from the Arctic to the Antarctic, this dynamic body of water provides diverse habitats for countless species, from microscopic organisms to the largest whales. These intricate ecosystems contribute substantially to planetary biodiversity.
Defining Characteristics of the Atlantic Ocean
The Atlantic Ocean is characterized by its elongated “S” shape, dividing it into North and South Atlantic. Down its center runs the Mid-Atlantic Ridge, the world’s longest mountain range, stretching approximately 16,000 kilometers from the Arctic to the Southern Ocean. This submerged range is a tectonic boundary where the North American and Eurasian plates, and the South American and African plates, slowly pull apart at about 2.5 centimeters per year, allowing magma to rise and create new seafloor.
An oceanic current, the Gulf Stream, originates in the Gulf of Mexico and flows north along the eastern U.S. coastline before veering east towards Northwest Europe as the North Atlantic Current. This warm, swift current influences the climate of coastal areas in the eastern United States, keeping them milder, and warms Western and Northern Europe. The Gulf Stream is part of the larger North Atlantic Gyre, a system of circulating currents that helps distribute heat across the ocean.
Key Ecosystems and Biodiversity
The Atlantic Ocean hosts diverse habitats and biological communities, including the Sargasso Sea. This distinctive North Atlantic region is defined by surrounding ocean currents, making it the only sea without a coastline. This two-million-square-mile ecosystem is characterized by free-floating Sargassum seaweed, which forms dense mats acting as a “golden rainforest of the high seas”.
These floating seaweed mats provide shelter, food, and nursery grounds for many marine species, including the Sargassum fish, and serve as a developmental habitat for juvenile loggerhead and green sea turtles. The Sargasso Sea is also the only known spawning area for European and American eels, which undertake extensive migrations to reproduce in its waters.
Cold-water coral reefs form another Atlantic ecosystem, found in the deep waters of the North Atlantic, often at depths between 200 and 2,000 meters. Unlike tropical corals, these species do not rely on sunlight; instead, they capture food particles from the water. Lophelia pertusa is a dominant reef-building coral, forming complex structures that provide habitat for over 1,300 associated species, including sponges, worms, starfish, and deep-sea fish. These ancient reefs, some thousands of years old, are found in areas like the Norwegian margin, off Scotland, and along the U.S. southern Atlantic seaboard.
Iconic Marine Species of the Atlantic
The North Atlantic right whale (Eubalaena glacialis) is one of the world’s most endangered whale species, with a population estimated around 360 individuals. These baleen whales feed on tiny crustaceans called copepods, straining them from the water using their baleen plates. They undertake seasonal migrations, moving from feeding grounds in the Labrador Sea, Gulf of Maine, and Gulf of St. Lawrence to warmer calving grounds off Georgia and Florida during winter.
The Atlantic bluefin tuna (Thunnus thynnus) is a highly migratory top predator in the pelagic food web. These powerful fish consume a diverse diet, including mackerel, herring, sand lance, anchovy, squid, and crustaceans, often adapting their diet to available prey. Bluefin tuna undertake extensive trans-Atlantic migrations between feeding grounds like the North Sea, Iceland Basin, and the Bay of Biscay, and their spawning areas, primarily in the Mediterranean Sea.
The leatherback sea turtle (Dermochelys coriacea) is the largest living turtle, identifiable by its leathery, ridged carapace. These highly migratory reptiles travel thousands of kilometers annually between tropical nesting beaches and colder foraging grounds in the North Atlantic, including areas off Canada, Newfoundland, and the North Sea. Leatherbacks are specialized feeders, with mouths adapted to consume soft-bodied prey like jellyfish and salps. Their large body size, thick fat layer, and specialized blood vessel networks allow them to maintain body heat and thrive in cold waters, unlike other sea turtle species.
Human Impact and Conservation
The Atlantic marine environment faces pressures from human activities. Overfishing has led to declines in fish populations, including Atlantic cod and deep-sea species, impacting the food web and causing habitat damage through practices like bottom trawling. Mismanagement and quotas exceeding scientific advice have contributed to the decline of commercially important species like mackerel and herring in the North-East Atlantic.
Plastic pollution is another threat, with recent studies suggesting the Atlantic Ocean may hold significantly more plastic, particularly microplastics, than previously estimated. These tiny plastic fragments, found in the upper 200 meters, are ingested by marine animals, potentially introducing toxic pollutants into the food chain and causing physical harm through entanglement.
Climate change is warming the Atlantic Ocean, with regions like the Gulf of Maine experiencing faster warming than the global average. This warming contributes to the weakening of the Atlantic Meridional Overturning Circulation (AMOC), a system of currents that transports heat, with projections indicating an 18 to 43 percent weakening by the end of the 21st century. Such changes can alter regional temperatures, accelerate sea-level rise along the North American coast, and intensify Atlantic storms.
In response to these challenges, conservation efforts are underway. International agreements, such as the High Seas Treaty, aim to protect marine biodiversity beyond national jurisdictions, supporting the global goal of protecting 30 percent of oceans by 2030. The establishment and expansion of Marine Protected Areas (MPAs) are also gaining momentum. Examples include the Azores protecting 30 percent of its surrounding waters and the North Atlantic Current and Evlanov Sea basin MPA (NACES MPA) in the North-East Atlantic, which covers nearly 600,000 square kilometers and has been expanded to include the seabed and deep-sea habitats.