Heat and Freshwater


The role of the Southern Ocean in the global heat and freshwater balance

Changes in the polar water cycle will have global impacts due to the sensitivity of the overturning circulation and heat transport to changes in freshwater input (Broecker, 1997; Clark et al., 2002). Observations suggest that changes in the global water cycle may already be apparent in changes in ocean stratification (e.g. Durack and Wijffels, 2010). The stratification of the Southern Ocean is delicately poised and particularly sensitive to changes in the freshwater balance (Gordon, 1991). Substantial uncertainty remains with regard to the high-latitude contributions to the global water cycle, the sensitivity of the water cycle to climate change and variability, and the impact of changes in the high-latitude water cycle on the remainder of the globe. 
Freshwater fluxes from melting sea ice, sub-ice shelf melting and precipitation are of the same order of magnitude in the Southern Ocean, and all three components need to be measured. Variables that need to be measured include atmospheric circulation (winds, storms, evaporation, precipitation, moisture flux); the horizontal and vertical circulation of the ocean, including exchange between high and low latitudes and the circulation beneath the sea ice, through the annual cycle; sea ice extent, thickness and distribution; and the contribution of glacial ice (ice shelf melt and iceberg production). New satellites promise synoptic observations of aspects of the freshwater balance, including snow and ice thickness, that cannot be measured at high spatial or temporal resolution using conventional means, but these new sensors are in critical need of data sets for validation.

Schematic of the key elements of a Southern Ocean air-sea flux observing system (Newman et al., 2019). Click on the image to download.

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.
Theme 1 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.

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

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)
  4. Antarctic Climate Change in the 21st Century (AntClim21)
  1. Argo
  2. The Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP)
  3. Marine Mammals Exploring the Oceans Pole to Pole (MEOP)
  4. OceanSITES

Key Documents

Cited References

  • Broecker, W.S., 1997: Thermohaline circulation the Achilles heel of our climate system: Will man-made COupset the current balance? Science, 278: 1582-1588.
  • 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.
  • Durack, P.J. and Wijffels, S.E., 2010: Fifty-year trends in global ocean salinities and their relationship to broad-scale warming, Journal of Climate, 23: 4342-4362.
  • Gordon, A.L., 1991: Two stable modes of Southern Ocean stratification, In: P.C. Chu and J.C. Gascard (Eds.), Deep convection and deep water formation in the oceans, Elsevier Science Publishers.