The Overturning Circulation


The stability of the Southern Ocean overturning circulation

Climate models suggest the overturning circulation in both the Northern and Southern hemispheres is sensitive to climate change (e.g. IPCC, 2007). Enhanced greenhouse warming is expected to drive a more vigorous hydrological cycle, with increased precipitation at high latitudes and increased evaporation at low latitudes. The resulting reduction in surface salinity reduces the formation of dense water at high northern and southern latitudes. Palaeoclimate records demonstrate that changes in the overturning circulation have been associated with large and abrupt climate changes in the past (e.g. Clark et al., 2002). Southern Ocean overturning is thought to exert a strong control on global productivity and CO2 (Marinov et al., 2006), and changes in strength of the Southern Ocean overturning circulation have been linked to changes in the ocean uptake and release of carbon dioxide, both in the present-day ocean and in association with glacial–interglacial cycles. Sustained observations of temperature, salinity, stratification and ventilation are needed to detect changes in the overturning in response to changes in atmospheric forcing. The observations need to span the entire water column, and need to include carbon, oxygen and other tracers.

Priority Observations

At the 2013 Scientific Steering Committee meeting in Shanghai, China, the SOOS Steering Committee identified the top gaps in observations for each of the 6 SOOS Science Themes that should be identified as "priority observations" for the coming years. SOOS encourages the community to develop field initiatives to address these key gaps and to highlight their contribution to the international SOOS effort through SOOS endorsement or other connections.

Schematic of the key elements of a Southern Ocean air-sea flux observing system (Newman et al., 2019). Click on the image to download.
Theme 2 Priority Observations
SOOS has identified a list of candidates for consideration as EOVs. The SOOS physical oceanographic variables build on the efforts of GCOS-OOPC-GOOS. Air-sea flux variables have been developed through the SOOS Air-Sea Flux Task Tem and resulting workshop and have recently been approved by GCOS for inclusion in the global Essential Climate Variable (ECV) list.

Key Observation Platforms

Repeat Hydrography, Argo floats, gliders, underway observations from ships, animal-borne sensors, surface drifters, bottom landers, moorings and sea-ice drifters.

Key Communities

  1. CLIVAR-CliC-SCAR Southern Ocean Regional Panel (SORP)
  2. Antarctic Sea Ice Processes and Climate (ASPeCt)
  3. Ocean Observations Physics and Climate Panel (OOPC)
  1. Argo
  2. GO-SHIP
  3. MEOP
  4. OceanSITES

Schematic of the observational platforms required to observe the Antarctic Bottom Water formation (Newman et al., 2019). Click on the image to download.

Key Documents

Cited References

  1. IPCC, 2007: Climate Change 2007: Synthesis report. Summary for Policymakers. Intergovernmental Panel on Climate Change, Geneva, Switzerland.
  2. Clark, P.U., Pisias, N.G., Stocker, T.F. and Weaver, A.J., 2002: The role of the thermohaline circulation in abrupt climate change, Nature, 415: 863-869.
  3. Marinov, I., Gnanadesikan, A., Toggweiler, J.R. and Sarmiento, J.L., 2006: The Southern Ocean biogeochemical divide, Nature, 441: 964-967.