- Also called:
- Global Ocean Conveyor or Great Ocean Conveyor Belt
- Related Topics:
- ocean current
- abyssal circulation
thermohaline circulation
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What is thermohaline circulation?
Thermohaline circulation is a crucial component of general ocean circulation, driven by temperature and salinity differences. This process involves the continuous replacement of deep seawater with surface water and the gradual replacement of surface water with water rising from deeper areas.
Thermohaline circulation moves significant volumes of water, which transports heat, nutrients, and other materials across vast distances. It also drives warmer surface waters from the subtropics toward the poles, which helps to regulate the climate of Iceland and coastal Europe. Some scientists believe that global warming could disrupt thermohaline circulation by introducing large amounts of fresh water into the North Atlantic Ocean from melting ice sheets and glaciers, which would reduce the density of surface waters and inhibit sinking motion that drives thermohaline circulation.
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How do temperature and salt (salinity) affect ocean water movement?
Thermohaline circulation, a crucial component of ocean circulation, is driven by temperature and salinity differences.
Temperature:
* Cooling increases seawater density, causing it to sink, primarily in polar regions.
* Surface cooling in fall causes the surface water to sink, and convective overturn proceeds as the density of the surface water increases with the decreasing temperature.Salinity:
* Increased salinity also raises density, leading to sinking.
* The amount of salt in seawater varies because of the addition or removal of water locally (e.g., through precipitation and evaporation).
* Evaporation and ice formation increase salinity and density.This interplay of temperature and salinity creates density gradients that drive the movement of water masses, influencing global heat distribution and climate patterns.
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What is the 'global conveyor belt' in the ocean?
The thermohaline circulation, also known as the "global conveyor belt," is a crucial component of general ocean circulation driven by temperature and salinity differences. This process involves the continual replacement of seawater at deep levels with water from the surface and the gradual replacement of surface water with water rising from deeper depths.
The circulation is initiated by the sinking of cold water in polar regions, mainly in the northern North Atlantic and near Antarctica. These dense water masses then spread throughout the ocean, eventually upwelling to sustain a slow return flow to the sinking regions. This movement transports heat, nutrients, and other materials across vast distances, playing a significant role in regulating regional and global climate.
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How does thermohaline circulation move warm and cold water around the Earth?
Thermohaline circulation (THC) is a vital part of ocean circulation, driven by temperature and salinity differences. In polar regions, cooling or net evaporation increases seawater density, causing it to sink. This sinking water is replaced by surface water, initiating the circulation.
The THC moves warm surface waters from the subtropics towards the poles, moderating the climate in regions like Iceland and coastal Europe. Cold water sinks in the North Atlantic and near Antarctica, spreading throughout the ocean and gradually rising to create a slow return flow. This process transports heat, nutrients, and other materials across vast distances, playing a crucial role in the global climate system.
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Why is thermohaline circulation important for marine life and climate?
Thermohaline circulation is vital for marine life and climate because it moves tremendous volumes of water, which transports heat, nutrients, solids, and other materials vast distances. This circulation moderates the climate of Iceland and coastal Europe by driving warmer surface waters poleward from the subtropics. Marine organisms are influenced by these circulation patterns, which determine the range of species and affect the distribution patterns of pelagic organisms. Some scientists believe that global warming could shut down this ocean current system by creating an influx of freshwater, which would lower the density of the surface waters and thus inhibit the sinking motion that drives large-scale thermohaline circulation.
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How could climate change affect thermohaline circulation in the future?
Climate change could significantly affect thermohaline circulation (THC) in the future. Some scientists suggest that global warming might disrupt this ocean current system due to an influx of fresh water from melting ice sheets and glaciers into the subpolar North Atlantic Ocean. Because fresh water is less dense than saline water, a substantial intrusion of fresh water could decrease the density of surface waters, thereby impeding the sinking motion that drives large-scale THC.
While some scientists once speculated that such changes could trigger colder conditions in regions surrounding the North Atlantic, experiments with modern climate models suggest that this is unlikely. Instead, a moderate weakening of the THC might occur, leading to a dampening of surface warming, rather than actual cooling, in the higher latitudes of the North Atlantic Ocean.
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thermohaline circulation (THC), the component of general oceanic circulation controlled by horizontal differences in temperature and salinity. It continually replaces seawater at depth with water from the surface and slowly replaces surface water elsewhere with water rising from deeper depths. Although this process is relatively slow, tremendous volumes of water are moved, which transport heat, nutrients, solids, and other materials vast distances. Thermohaline circulation also drives warmer surface waters poleward from the subtropics, which moderates the climate of Iceland and other coastal areas of Europe.
A brief treatment of thermohaline circulation follows. For full treatment, see Ocean current: Two types of ocean currents: Thermohaline circulation.
The general circulation of the oceans consists primarily of wind-driven ocean currents. These, however, are superimposed on the much more sluggish circulation driven by horizontal differences in temperature and salinity—namely, thermohaline circulation. Wind-driven circulation, which is strongest in the surface layer of the ocean, is the more vigorous of the two and is configured as large gyres that dominate an ocean region. In contrast, thermohaline circulation is much slower, with a typical speed of 1 centimetre (0.4 inch) per second, but this flow extends to the seafloor and forms circulation patterns that envelop the global ocean.
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In some areas of the ocean, generally during the winter season, cooling or net evaporation causes surface water to become dense enough to sink. Convection penetrates to a level where the density of the sinking water matches that of the surrounding water. It then spreads slowly into the rest of the ocean. Other water must replace the surface water that sinks. This sets up the thermohaline circulation. The basic thermohaline circulation is one of sinking of cold water in the polar regions, chiefly in the northern North Atlantic—where the circulation is often referred to as the Atlantic Meridional Overturning Circulation (AMOC)—and near Antarctica. These dense water masses spread into the full extent of the ocean and gradually upwell to feed a slow return flow to the sinking regions. The theory for the thermohaline circulation pattern was first proposed by Henry Stommel and Arnold Arons in 1960.
Some scientists believe that global warming could shut down this ocean current system by creating an influx of freshwater from melting ice sheets and glaciers into the subpolar North Atlantic Ocean. Since freshwater is less dense than saline water, a significant intrusion of freshwater would lower the density of the surface waters and thus inhibit the sinking motion that drives large-scale thermohaline circulation. It has also been speculated that, as a consequence of large-scale surface warming, such changes could even trigger colder conditions in regions surrounding the North Atlantic. Experiments with modern climate models suggest that such an event would be unlikely. Instead, a moderate weakening of the thermohaline circulation might occur that would lead to a dampening of surface warming—rather than actual cooling—in the higher latitudes of the North Atlantic Ocean. See also ocean current.