Seminars

Seminar Abstract

Formation of subantarctic mode water in the Southeastern Indian Ocean

Subantarctic Mode Water 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 2000 meters, 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 oS, 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 of roughly equal importance. Within the formation area, the Ekman contribution dominates and leads to an downstream evolution of mode water properties.

[Back to Seminars]

CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
Karen Wild-Allen, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5010
Piers Dunstan, (Biological seminars) CSIRO Marine and Atmospheric Research (03) 6232 5382
Sandra Zicus, Antarctic Climate and Ecosystems CRC (03) 6226 7888 & Institute of Antarctic and Southern Ocean Studies (IASOS) University of Tasmania (03) 6226 2509