Processes
Thermohaline Circulation
thur-moh-HAY-leen
Also Known As Great Ocean Conveyor Belt
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The slow, density-driven part of the global ocean circulation, set in motion where cold, salty surface water grows dense enough to sink, notably in the North Atlantic and around Antarctica, and balanced by upwelling and surface return flows elsewhere. Because it moves heat between hemispheres and stores carbon in the deep ocean, its stability is a central question of modern climate science.
Facts
TimescaleA single circuit of the global overturning takes on the order of a thousand years 1 Driving ForceDifferences in seawater density created by variations in temperature and salinity, principally the cooling and sinking of dense, salty water at high latitudes. 1 Resulting FeatureA deep, slow global circulation, popularly called the ocean conveyor belt, that moves heat between ocean basins over centuries. 1 SignificanceThermohaline circulation, particularly the Atlantic branch known as the AMOC, redistributes enough heat to moderate the climate of western Europe; whether it is weakening as polar ice melt freshens the surface ocean is an active scientific question. 1 Cross-Tradition Connections
Associated With
Together with ocean circulation it redistributes thermal energy across Earth's surface.
Wind driving and the global overturning circulation both feed the Gulf Stream; its northern extension carries part of the overturning's warm upper limb.
The overturning circulation is balanced by upwelling and surface return flows.
In Discipline
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Open Questions (1 open question)
Is the Atlantic Meridional Overturning Circulation Approaching a Tipping Point?
Direct measurement since the mid-2000s and proxy reconstructions suggest the Atlantic branch of the thermohaline circulation, the AMOC, has weakened, but as of the mid-2020s there is no scientific consensus on whether a consistent slowing has actually occurred, how much of any weakening reflects climate change versus natural multi-decadal variability, or whether an abrupt collapse could arrive within this century rather than the more gradual decline most comprehensive climate models project.
What would resolve this A longer continuous observational record of the overturning circulation's strength, and climate models whose treatment of Atlantic freshwater transport can be tested against that record rather than relying on simulations some researchers argue understate collapse risk.
Oceanography and ClimatologyThermohaline Circulation (Wikipedia)
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