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| thermohaline circulation | |
|---|---|
| Name | Thermohaline circulation |
| Caption | Global schematic of deep ocean currents |
| Type | Ocean circulation |
| Location | World Ocean |
thermohaline circulation
Thermohaline circulation is a component of global ocean circulation driven by seawater density differences caused by variations in temperature and salinity. It links surface currents, deep-water formation sites, and abyssal flows, interacting with atmospheric systems, cryospheric processes, and large-scale climate modes. Major scientific institutions, national research programs, and historical expeditions have advanced understanding through observation, theory, and modelling.
Thermohaline circulation operates at the intersection of oceanography, climatology, and paleoclimatology, connecting regions such as the North Atlantic, Southern Ocean, and North Pacific with polar processes and equatorial upwelling. Studies by institutions including National Oceanic and Atmospheric Administration, Scripps Institution of Oceanography, Woods Hole Oceanographic Institution, British Antarctic Survey, and Alfred Wegener Institute integrate shipboard surveys, satellite missions like TOPEX/Poseidon, and long-term arrays such as the Argo float program. Historical expeditions from the era of HMS Challenger to modern projects such as CLIVAR and GEOTRACES have mapped the pathways and quantified rates.
Density-driven flow arises from thermodynamic and buoyancy processes studied by researchers associated with Royal Society, Max Planck Institute for Meteorology, and university departments including Massachusetts Institute of Technology and University of Oxford. Cooling at high latitudes, brine rejection during sea ice formation near Greenland, Antarctic Peninsula, and Weddell Sea increases salinity and density, promoting convection and deep-water formation. Wind forcing from systems like the North Atlantic Oscillation and Southern Annular Mode modulates surface transport, while mixing at boundaries influenced by topographic features such as the Mid-Atlantic Ridge and Kerguelen Plateau transfers momentum and tracers between layers. Physical frameworks employ the Navier–Stokes equations applied in models developed at European Centre for Medium-Range Weather Forecasts and Princeton University.
Canonical pathways include northward warm surface currents such as the Gulf Stream and North Atlantic Drift, site-specific deep-water production in the Labrador Sea and Norwegian Sea, and southward abyssal flows traversing basins and circumpolar routes around Antarctica via the Antarctic Circumpolar Current. Water mass classifications like North Atlantic Deep Water, Antarctic Bottom Water, and Intermediate water describe origin and properties, documented in basin surveys by the International Geosphere-Biosphere Programme. Boundary currents, gyres such as the North Pacific Gyre and South Atlantic Gyre, and exchanges through straits including Denmark Strait and Drake Passage shape connectivity.
Thermohaline circulation redistributes heat, influencing regional climates in areas linked to the North Atlantic Drift and affecting monsoon systems studied in conjunction with institutions like Indian Institute of Tropical Meteorology. Changes in circulation alter carbon uptake and biogeochemical cycles addressed by programs such as International Ocean Carbon Coordination Project and affect ecosystems from plankton communities observed by Census of Marine Life to fisheries managed under organizations like Food and Agriculture Organization. Abrupt rearrangements have been implicated in past societal impacts during events examined by historians of the Little Ice Age and investigators of abrupt climate change at Lamont–Doherty Earth Observatory.
Variability spans seasonal to millennial scales and is analyzed in context with modes like the Atlantic Multidecadal Oscillation and El Niño–Southern Oscillation. Interannual fluctuations link to climate indices monitored by National Aeronautics and Space Administration and seasonal prediction centers, while basin-wide shifts occur over decades and longer as explored in long-term datasets curated by International Council for the Exploration of the Sea. Theoretical work by researchers affiliated with Sverdrup Laboratory and Woods Hole quantifies overturning rates, often expressed in Sverdrups, and contrasts rapid surface adjustments with slow abyssal transit times.
Proxy records from ice cores at Greenland ice sheet and Antarctic ice sheet, marine sediment cores from sites investigated under International Ocean Discovery Program, and speleothems studied by teams at University of Bern provide evidence of past circulation changes. Episodes such as Heinrich events and the Younger Dryas are associated with reorganization of deep circulation, inferred from isotopic signatures (oxygen isotopes), sediment provenance, and microfossil assemblages analyzed by paleoclimatologists at Lamont–Doherty Earth Observatory and Geological Survey of Denmark and Greenland.
Direct observations combine moored arrays like RAPID monitoring, hydrographic sections from cruises, and autonomous platforms from programs including SOCCOM and ARGO. Numerical modelling uses coupled atmosphere–ocean general circulation models produced by centers including Met Office Hadley Centre, NOAA Geophysical Fluid Dynamics Laboratory, and the Max Planck Institute, with intercomparisons coordinated by the Coupled Model Intercomparison Project. Data assimilation and ensemble techniques developed at European Centre for Medium-Range Weather Forecasts improve projections and attribution studies.
Anthropogenic forcing from greenhouse gas emissions assessed by the Intergovernmental Panel on Climate Change and land-ice mass loss monitored by ICESat and GRACE influence surface buoyancy budgets and freshwater input from melting of Greenland ice sheet and Antarctic ice shelves. Scenario-based model projections suggest potential weakening or reorganization with societal implications debated in assessments by World Meteorological Organization and policy bodies. Adaptation and mitigation strategies are informed by interdisciplinary research involving universities such as University of Cambridge and agencies including European Space Agency.
Category:Ocean circulation