South Atlantic Meridional Overturning Circulation

South Atlantic Meridional Overturning Circulation
Name	South Atlantic Meridional Overturning Circulation
Other names	SAMOC
Region	South Atlantic Ocean
Type	Ocean circulation
Components	Atlantic Meridional Overturning Circulation; Antarctic Circumpolar Current; Benguela Current
Significance	Heat transport; carbon uptake; climate variability

South Atlantic Meridional Overturning Circulation The South Atlantic Meridional Overturning Circulation is a zonally integrated component of the Atlantic overturning system linking the Antarctic Circumpolar Current, Brazil Current, Benguela Current, and the basin-scale return flow, and it influences climate phenomena such as the El Niño–Southern Oscillation, South Atlantic Convergence Zone, and variability recorded in the Interdecadal Pacific Oscillation. Major institutions including the National Oceanic and Atmospheric Administration, WOCE, CLIVAR, and the Global Ocean Observing System have prioritized its observation because of connections to the Atlantic Meridional Overturning Circulation, Atlantic Multidecadal Variability, and the instrumental records used by the Intergovernmental Panel on Climate Change.

Overview and Definitions

The circulation is defined in terms of meridional volume and heat transport across sections between the Equator, Cape of Good Hope, and South America, and is often characterized by streamfunction metrics used by researchers at Scripps Institution of Oceanography, Plymouth Marine Laboratory, Lamont–Doherty Earth Observatory, and the National Centre for Polar and Ocean Research. Definitions used in reports from the European Union and agencies such as the UK Met Office and NASA employ density-class overturning, layer decomposition, and water-mass transformation frameworks originally formalized in studies associated with the Geophysical Fluid Dynamics Laboratory and the Woods Hole Oceanographic Institution. Standardized indices reference cross-basin sections at locations near 34°S, the Walvis Ridge, and passages adjacent to Tristan da Cunha and Gough Island.

Physical Mechanisms and Structure

Mechanisms link surface wind forcing from the South Atlantic High, buoyancy forcing influenced by exchanges with the Southern Ocean, and eddy processes tied to the Antarctic Circumpolar Current and mesoscale variability observed by Argo floats managed by programs like the Global Argo and Argo-France collaborations; bathymetric steering by the Mid-Atlantic Ridge, Ridge of Atlantis, and the Walvis Ridge controls pathways of Northward Deep Water and Antarctic Intermediate Water, while western boundary currents such as the Brazil Current and eastern boundary upwelling systems like the Benguela Current modulate upper-ocean return flow. Interactions with convective sites near the Weddell Sea, influences from polar frontal systems associated with the Southern Ocean fronts, and mixing over features like the Rio Grande Rise and Vema Seamount contribute to overturning cell formation documented by teams from the University of Cape Town, University of São Paulo, and CSIR.

Role in Global Climate and Heat Transport

The South Atlantic component redistributes heat between the Southern Ocean and the North Atlantic Ocean, affecting heat budgets used in projections by the IPCC and modulating sea-surface temperature patterns linked to the El Niño–Southern Oscillation and Atlantic Niño; teleconnections extend to the Amazon rainforest rainfall variability, the Sahel precipitation, and the frequency of extreme events assessed by the World Meteorological Organization and ECMWF. Its contribution to poleward heat transport is quantified alongside fluxes through the Drake Passage and exchanges with the Indian Ocean via the Agulhas Current, with implications for polar ice mass balance studied by researchers at the British Antarctic Survey, NASA Jet Propulsion Laboratory, and the European Space Agency.

Variability, Observations, and Monitoring

Observational efforts combine repeat hydrographic sections from programs like GO-SHIP, sustained mooring arrays modeled on the RAPID project but deployed along South Atlantic transects, satellite altimetry from TOPEX/Poseidon successors, and biogeochemical sensors on Argo floats and gliders supported by institutions such as the National Science Foundation, GEOMAR, and the Instituto Oceanográfico. Variability on seasonal to decadal timescales has been linked to atmospheric modes including the Southern Annular Mode, North Atlantic Oscillation, and remote forcing from the Pacific Decadal Oscillation noted in paleoarchives like marine sediment cores and Antarctic ice cores collected by expeditions coordinated by the Scientific Committee on Antarctic Research.

Modeling, Projections, and Uncertainty

Global and regional models from centers such as the Met Office Hadley Centre, GFDL, NCAR, and the Max Planck Institute for Meteorology simulate the South Atlantic overturning within coupled frameworks evaluated by the CMIP multimodel ensemble used in IPCC assessments, yet projections differ because of uncertainties in representation of mesoscale eddies, convective mixing, and air–sea flux parameterizations tested in intercomparison projects like OMIP and CMIP6. Scenario-dependent changes under Representative Concentration Pathway 8.5 and Shared Socioeconomic Pathway narratives show potential weakening, shifts in water-mass pathways, and altered heat uptake with consequences debated in publications by the Royal Society and policy analyses from the European Commission.

Impacts on Marine Ecosystems and Biogeochemistry

Changes in overturning affect nutrient supply to the Benguela upwelling system, productivity patterns important to fisheries managed under agreements like the South Atlantic Fisheries Commission, and carbon uptake processes monitored by the Global Carbon Project and programs coordinated by the International Ocean Carbon Coordination Project. Shifts influence distribution of species such as Atlantic salmon, migrations of tuna stocks, the health of coral communities studied by the International Coral Reef Initiative, and oxygenation linked to hypoxic events observed in shelf regions by researchers at the National Oceanography Centre, Universidade de São Paulo, and conservation bodies like IUCN.

Category:Oceanography