Ocean Dynamics

, Volume 56, Issue 5–6, pp 525–542 | Cite as

Formation of subantarctic mode water in the southeastern Indian Ocean

  • Jean-Baptiste Sallée
  • Nicolas Wienders
  • Kevin Speer
  • Rosemary Morrow
Original paper

Abstract

Subantarctic Mode Water (SAMW) is the name given to the relatively deep surface mixed layers found directly north of the Subantarctic Front in the Southern Ocean, and their extension into the thermocline as weakly stratified or low potential vorticity water masses. The objective of this study is to begin an investigation into the mechanisms controlling SAMW formation, through a heat budget calculation. ARGO profiling floats provide estimates of temperature and salinity typically in the upper 2,000 m and the horizontal velocity at various parking depths. These data are used to estimate terms in the mode water heat budget; in addition, mode water circulation is determined with ARGO data and earlier ALACE float data, and climatological hydrography. We find a rapid transition to thicker layers in the central South Indian Ocean, at about 70°S, associated with a reversal of the horizontal eddy heat diffusion in the surface layer and the meridional expansion of the ACC as it rounds the Kerguelen Plateau. These effects are ultimately related to the bathymetry of the region, leading to the seat of formation in the region southwest of Australia. Upstream of this region, the dominant terms in the heat budget are the air–sea flux, eddy diffusion, and Ekman heat transport, all having approximately equal importance. Within the formation area, the Ekman contribution dominates and leads to a downstream evolution of mode water properties.

Notes

Acknowledgements

The ARGO data were collected and made freely available by the International ARGO Project and the national programs that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org). ARGO is a pilot program of the Global Ocean Observing System. This study was supported by the French PATOM and Coriolis programs and by NSF grants OCE 0336697 and OCE 0117618 to K. Speer.

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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Jean-Baptiste Sallée
    • 1
  • Nicolas Wienders
    • 2
  • Kevin Speer
    • 2
  • Rosemary Morrow
    • 1
  1. 1.LEGOS-UMR5566ToulouseFrance
  2. 2.Department of Oceanography, OSB 435Florida State UniversityTallahasseeUSA

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