Atlantic Ocean

The Atlantic Ocean is the second-largest of the world’s oceans, with an area of about 106,460,000 km2 (41,100,000 sq mi).[2][3] It covers approximately 20 percent of Earth’s surface and about 29 percent of its water surface area. It is known to separate the “Old World” of Europe and Asia from the “New World” of the Americas in the European perception of the World.

The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, and the Americas to the west. As one component of the interconnected World Ocean, it is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, and the Southern Ocean in the south (other definitions describe the Atlantic as extending southward to Antarctica). The Atlantic Ocean is divided in two parts, by the Equatorial Counter Current, with the North(ern) Atlantic Ocean and the South(ern) Atlantic Ocean at about 8°N.

The Equatorial Counter Current subdivides it into the North Atlantic Ocean and the South Atlantic Ocean at about 8°N, with the North Atlantic Ocean experiencing frictional counter-clockwise circulation, and the South Atlantic experiencing a clockwise circulation. The largest river basin in the Atlantic is the Amazon River basin.

The highest point in the Atlantic is either Gavín or Monte Agudo on Greenland (the exact location of its summit), depending on whether Central Antarctica is considered a part of the continent. Its lowest point is either Depression Valley or Challenger Deep, which are located in Antarctica.[4]

It has an average salinity of 35 parts per thousand (ppt) (1.2%).

The density of the water is 2.6 g/cm³ (0.065 atm), which is less than that of fresh water.[5] It freezes at about 0°C along the north-east coast of Greenland during winter and summer, with the lowest recorded value of −14°C in 1901,[6] but varies greatly in different areas. Ice forms only around Antarctica, where ice shelves or sea ice is widespread, and near African and European coasts.
The ocean’s principal water mass is called Atlantic Deep Water (ADW), which separated from the general circulation of the world ocean about 5 million years ago. Most of the water mass in the Atlantic is distributed by polar currents, which are river-like features that flow northwards from the mid-latitudes of each continent to feed into wider oceans, called “conveyor belts” by oceanographers. As with all currents, there is a ring current surrounding each continent which is maintained by winds. In the North Atlantic, a branch of the Gulf Stream is a major component of the ring current. In turn, the Sargasso Sea has a wide counterclockwise circulation. Within this general circulation on both sides of the Atlantic basin are two large meanders, one off each coast of North America, which flow westwards from their centers on each continent towards their eastern coasts.[7]

The climate in the open ocean outside these currents is extremely varied and changes rapidly. Overall, there is little seasonal temperature variation due to heat storage within the ocean and little transfer of heat from or to adjacent land masses through currents or by tides that can exceed 20 m (66 ft) in vertical height. The ocean has a mean salinity of 35 parts per thousand (ppt) (1.2%).

It is estimated the Atlantic accounts for about one-third of the global production of precipitated carbon in the atmosphere.[8] The Atlantic sets the phase for the thermohaline circulation, which has a role in determining climate patterns in both hemispheres. The influence of the thermohaline circulation on climate, known as the Atlantic multi-decadal oscillation (AMO), is seen in pressure patterns throughout the North Atlantic and in surface temperature fluctuations.

Large quadrupole moments are associated with this oscillation dominating temporal variability of both atmospheric pressure patterns and sea ice distribution.[9]

Water mass distribution within the Atlantic Ocean. The blue-shaded region shows where water with a salt content between 35 and 37 ppt is currently welling up from, due to salinity at depth being higher than at surface. This is also known as Upper Salinity Maximum. The thin blue-shaded area shows where aridity is lowest, i.e. where evaporation is greater than precipitation. The yellow-shaded region shows the maximum density of the water occurring at the surface, i.e., it shows where isopycnals are deepest. The red-shaded region shows water sinking due to its salt content being lighter than the surrounding waters, which is also known as Lower Salinity Maximum. Note that this data only represents a snapshot in time and does not represent circulation throughout the year.

The role of water in the Atlantic is one of deep importance. The Gulf Stream, a western boundary current, is the largest and fastest-moving warm-water current in the world and is responsible for keeping Europe warmer than any other continent at similar latitudes. It originates at the tip of Florida and enters the Atlantic Ocean near Georgia at latitude 30° N. From there it moves northward, transmitting its warmth to the surrounding continents. This warm water promotes evaporation from ocean surfaces, giving rise to concentrations of water vapor in the air (the SST anomaly) that are one index used to estimate global climate anomalies for this region. This surface current is also responsible for delivering heat to the deep ocean, which raises its temperature and thus promotes evaporation from its surface as well. The Gulf Stream delivers about half of the heat carried away from Europe by northern currents.

The Atlantic meridional overturning circulation (AMOC) is a large-scale chemical transport process that redistributes heat northwards, and thus warms areas adjacent to the Gulf Stream. It has been weakening and decelerating (known as a “states of flow”) since at least about 1970. This slowdown has been linked to climate change. It is believed that the AMOC could collapse in the future if the West Antarctic Ice Sheet collapses.

The Gulf Stream, which turns clockwise in the Northern Hemisphere, drives towards Europe, while warm water flows northwards along the North American coast. Eventually this flow reaches Greenland. Then it sinks into the North Atlantic.[10] The cold fresh water of eastern Canada melts sea ice covering Greenland, causing strong currents which flow eastward across Canada. These currents bring warm water to both sides of Greenland, but are offset by countercurrents which are driven by Greenland’s relative vertical heat flux.[11]

The Labrador current transports warm water to Europe where it warms up frozen regions of Scandinavia and Russia along its way.

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