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Motivation: We know that Southern Ocean is warming. How does this affect the watermass formation?

Evidence of Decadal Fluctuations in the Water Mass Properties in the Atlantic sector of the Southern Ocean. E. Fahrbach, Axel Behrendt, Olaf Boebel, Mario Hoppema, Olaf Klatt, Gerd Rohardt and Andreas Wisotzki Alfred-Wegener-Institut für Polar- und Meeresforschung

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Motivation: We know that Southern Ocean is warming. How does this affect the watermass formation?

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  1. Evidence of Decadal Fluctuations in the Water Mass Properties in the Atlantic sector of the Southern Ocean E. Fahrbach, Axel Behrendt, Olaf Boebel, Mario Hoppema, Olaf Klatt, Gerd Rohardt and Andreas Wisotzki Alfred-Wegener-Institut für Polar- und Meeresforschung in der Helmholtz-Gemeinschaft, Bremerhaven, Germany

  2. Motivation: We know that Southern Ocean is warming. How does this affect the watermass formation? By change of source water masses? By change of formation processes?

  3. The Weddell gyre circulation and the area of observations carried out during WECCON

  4. Water mass and temperature distributions at the Greenwich meridian ACC WDW CDW WSDW Maud Rise WSBW ANT XXII/3 2005 North South

  5. Area of WSBW decreased by 25% from 1992 to 2008 1992 2008

  6. Mean temperature and salinity in the deep water masses of the Weddell gyre at the Greenwich meridian WDW temperature increased until 1996 and decreased until 2005 and is increasing since. WSBW temperature is increasing since 1992. Salinity Potential temperature

  7. Depth of temperature maximum in WDW Thickness of the WDW layer Depth of the upper limit of the WDW (depth of pot.Temp = 0°C) Depth of the core of WW(temperature minimum)

  8. Temperature in the Warm Deep Water

  9. Warming and salinification affects the full depth Area on the transect with higher potential temperature and salinity as the long term average Increase of mean potential temperature and salinity on the transect

  10. Variations in the gyre circulation affect water mass properties by controlling the inflow of source water masses

  11. The Weddell gyre is not a closed system but open to the north and the east

  12. Dynamic topography along the Greenwich Meridian as indicator of the gyre intensity Dyn dm

  13. Large scale wind forcing and Weddell gyre flow Strong gyre is related to warm conditions - Weak gyre to cold conditions Weak west winds Strong east winds

  14. Weddell Sea bottom water properties in the Weddell Sea proper and the on the western slope

  15. The Weddell gyre circulation and the area of observations carried out during WECCON and CASO

  16. Warming of the deep water in the Weddell gyre 0.523 ANT VIII/2 1989 -0.922 AWI209 0.764 ANT XIII/4 1996 -0.862

  17. Entrainment of warmer and saltier WDW into the slope plume forms warmer and saltier WSBW. With the end of the WDW pulse WSBW began to cool.

  18. Temperature of the WSBW in the eastern Weddell sea At mooring AWI 209 from 1989 to 2008 50 m above bottom Temperature of the WSBW in the western Weddell Sea At mooring AWI 207 from 1989 to 2008 50 m above bottom

  19. Conclusions • Pronounced variations on a multi-annual time scales occur in the water mass properties of the Warm Deep, the Weddell Sea Deep and the Weddell Sea Bottom Water, the Winter Water and the winter sea ice thickness. • Whereas the overall average temperature and salinity are increasing on the Greenwich meridian over 24 years of observations, the source water is subject to decadal variations. • Whereas Weddell Sea Bottom Water is warming at the Greenwich Meridian, it is cooling in the Weddell Sea proper since the early 2000s. • Regional processes are able to transform time scales of external forcing into time scales of internal reaction. • To follow the ongoing variations a Southern Ocean Observing System (SOOS) is needed.

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