Sea level anomaly trends in the Southern Ocean: anthropogenic forcing or interannual variability? — Australian Meteorological and Oceanographic Society
  1. Schedule
  2. 02/03(i). Dynamics of the Southern Hemisphere oceans; bridging spatial scales in the ocean
  3. Sea level anomaly trends in the Southern Ocean: anthropogenic forcing or interannual variability?

Sea level anomaly trends in the Southern Ocean: anthropogenic forcing or interannual variability? (#74)

Amelie Meyer 1 , Clothilde Langlais 2 , Navid C. Constantinou 3 4 , Robert M. Graham 5 , Benoit Legresy 2 6 , Andrew McC. Hogg 3 4 , Nathan L. Bindoff 1 2 6
  1. ARC Centre of Excellence for Climate Extremes IMAS University of Tasmania, Hobart, TAS, Australia
  2. Marine and Atmospheric Research, CSIRO, Hobart, Australia
  3. Research School of Earth Science, Australian National University, Canberra, Australia
  4. ARC Centre of Excellence for Climate Extremes , Canberra, Australia
  5. Ocean & Sea Ice, Norwegian Polar Institute, Tromso, Norway
  6. Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Australia

Southern Ocean circulation strongly influences the global climate system. Eddy energy in the Southern Ocean is expected to rise with increasing strength of Southern Hemisphere westerly winds. Satellite altimetry data provides a 25-year time series (1993-2018) of sea surface height from which, observed trends in ocean Eddy Kinetic Energy can be derived. These trends currently show strong regional variability (Patara et al., 2016), with some estimates suggesting an overall mean increase in Southern Ocean EKE (Hogg et al, 2015), possibly dominated by regional extremes. Concurrently, both reanalysis products and models show intensification of Southern Hemisphere westerly winds with a poleward shift during the summer (DJF) period (Thompson and Solomon, 2002) and a 20% increase in wind stress forcing on the Southern Ocean during the 1980-2010 period (Swart & Fyfe, 2012; Farneti et al., 2015). Atmospheric and coupled GCM’s suggest that this wind stress increase is driven by both by the deepening of the ozone hole in the stratosphere and by increasing carbon dioxide (CO2) concentrations in the atmosphere during the 1980-2010 period (Gent, 2016, Swart et al., 2018).

Here we use existing observations, reanalysis products, and high-resolution ocean model data (0.1o) to estimate changes in Southern Ocean mesoscale circulation over the past 25 years, focusing on the oceanic standing meander between South Africa and the Kerguelen Islands.  The dynamics of this system and relative role of interannual variability and anthropogenic forcing are explored.

  1. Farneti R, Downes SM, Griffies SM, Marsland SJ, Behrens E, et al. 2015. An assessment of Antarctic Circumpolar Current and Southern Ocean meridional overturning circulation during 1958–2007 in a suite of interannual CORE-II simulations. Ocean Model. 93:84–120
  2. Gent, P. R., 2016: Effects of Southern Hemisphere wind changes on the meridional overturning circulation in ocean models. Annu. Rev. Mar. Sci., 8, 79–94, doi:https://doi.org/10.1146/annurev-marine-122414-033929.
  3. Hogg, A. McC., M. P. Meredith, D. P. Chambers, E. P. Abrahamsen, C. W. Hughes, and A. K. Morrison (2015), Recent trends in the Southern Ocean eddy field, J. Geophys. Res. Oceans, 120, 257–267, doi:10.1002/2014JC010470.
  4. Patara, L., C. W. Böning, and A. Biastoch (2016), Variability and trends in Southern Ocean eddy activity in 1/12° ocean model simulations, Geophys. Res. Lett., 43, 4517–4523, doi:10.1002/ 2016GL069026.
  5. Swart NC, Fyfe JC. 2012. Observed and simulated changes in the Southern Hemisphere surface westerly wind-stress. Geophys. Res. Lett. 39:L16711
  6. Swart, N. C., S. T. Gille, J. C. Fyfe, and N. P. Gillett, 2018: Recent Southern Ocean warming and freshening driven by greenhouse gas emissions and ozone depletion. Nat. Geosci., 1, doi:10.1038/s41561-018-0226-1.
  7. D. W. J. Thompson and S. Salomon (2002), Interpretation of Recent Southern Hemisphere Climate Change, Science, 296, 895-899, doi: 10.1126/science.1069270
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