South Atlantic Multidecadal Oscillation

South Atlantic Multidecadal Oscillation
Name	South Atlantic Multidecadal Oscillation
Abbreviation	SAMDO
Region	South Atlantic Ocean
Timescale	Multidecadal
Primary driver	Ocean circulation
Related	Atlantic Multidecadal Oscillation, Southern Annular Mode

South Atlantic Multidecadal Oscillation The South Atlantic Multidecadal Oscillation is a hypothesized basin-scale multidecadal variability mode in the South Atlantic Ocean linked to sea surface temperature variability and linked climate anomalies. Important to studies of twentieth- and twenty-first-century climate change, the phenomenon has been investigated in observational analyses, paleoclimate reconstructions, and coupled model experiments by institutions and researchers worldwide. Debates over its definition, indices, and relative roles compared to greenhouse gas forcing involve agencies, universities, and international programs.

Overview

The concept of multidecadal variability in the South Atlantic has been discussed in literature from groups including National Oceanic and Atmospheric Administration, National Aeronautics and Space Administration, Met Office Hadley Centre, Woods Hole Oceanographic Institution, and teams at Scripps Institution of Oceanography and Lamont–Doherty Earth Observatory. Studies contrast the South Atlantic phenomenon with the Atlantic Multidecadal Oscillation, and compare its phasing with modes such as the Southern Annular Mode, El Niño–Southern Oscillation, and influences from the Antarctic Circumpolar Current. Regional observational programs like R/V Meteor expeditions and initiatives by CSIR (South Africa) and Instituto Oceanográfico (Brazil) have provided datasets used to define indices.

Physical Mechanisms and Variability

Proposed mechanisms invoke interactions among the South Atlantic Current, gyre circulation, wind stress variability linked to the Southern Hemisphere westerlies, and advective processes tied to the South Equatorial Current and Benguela Current. Thermohaline contributions are examined alongside dynamical coupling with the Antarctic Intermediate Water and exchanges at boundaries with the North Brazil Current and Malvinas Current. Process studies reference numerical experiments from models developed at Geophysical Fluid Dynamics Laboratory, Max Planck Institute for Meteorology, Centre National de Recherches Météorologiques, and CSIRO. Observed multidecadal SST patterns are compared with variability in heat transport across the Brazil–Malvinas Confluence and teleconnections through the South Atlantic Convergence Zone.

Historical Observations and Indices

Indices have been constructed from in situ measurements collected by platforms such as Argo floats, tide gauge networks used by Permanent Service for Mean Sea Level, historical ship logs archived by International Comprehensive Ocean-Atmosphere Data Set, and satellite missions from NOAA, European Space Agency, and NASA. Paleoclimate proxies from cores studied by teams at Alfred Wegener Institute and University of Cape Town complement instrumental records. Authors have proposed basin-mean SST indices, EOF-based patterns, and filtered time series similar to approaches used for the Pacific Decadal Oscillation; differences among indices are discussed in assessments by Intergovernmental Panel on Climate Change authors.

Climate Impacts and Teleconnections

Correlations link the South Atlantic multidecadal signal to variability in regional rainfall patterns affecting South Africa, Brazil, Argentina, and Namibia, and to modulations of the South American Monsoon System and the West African Monsoon at subtropical latitudes. Impacts on marine ecosystems have been reported near the Patagonian Shelf, Benguela upwelling system, and Rio Grande Rise, with implications for fisheries managed by agencies such as Commission for the Conservation of Antarctic Marine Living Resources and national ministries. Atmospheric teleconnections are examined in the context of interactions with the Walker circulation, stratosphere–troposphere coupling studied by groups at National Center for Atmospheric Research, and remote influences on North Atlantic Oscillation–like patterns.

Detection, Attribution, and Modeling

Detection studies use statistical techniques developed by researchers at Princeton University, University of Oxford, and ETH Zurich to separate internal variability from forced trends identified in experiments coordinated by Coupled Model Intercomparison Project centers. Attribution analyses compare idealized control runs with historical and future scenario runs from centers including Japan Meteorological Agency, Canadian Centre for Climate Modelling and Analysis, and Institute Pierre-Simon Laplace. Limitations arise from model resolution, representation of mesoscale processes, and biases in reproducing the Benguela Current and southern subtropical gyre, leading to ongoing model intercomparison work in forums like World Climate Research Programme.

Regional Environmental and Societal Effects

Multidecadal SST variability alters sea level patterns relevant to ports such as Cape Town, Rio de Janeiro, and Buenos Aires, influences coastal upwelling that affects communities along the Namibian coast and Southeastern Brazil, and modulates extreme event probability with socioeconomic consequences assessed by United Nations Development Programme and national agencies. Fisheries, aquaculture, and tourism sectors respond to productivity shifts documented by regional research centers including Universidade de São Paulo and University of Cape Town, while policy-makers in national ministries and regional bodies consider these signals for adaptation strategies.

Future Projections and Uncertainties

Future behavior of the South Atlantic multidecadal variability in scenarios explored by IPCC AR6-aligned ensembles remains uncertain because of uncertainties in decadal predictability, anthropogenic forcing trajectories (e.g., commitments under Paris Agreement), and model bias. Ongoing observational expansion via Argo extensions, enhanced satellite missions from European Space Agency and NASA', coordinated modeling efforts at CMIP6 participants, and paleoclimate synthesis projects aim to reduce uncertainty and improve operational decadal prediction systems overseen by institutions like WMO.

Category:Oceanography