Scientific Objectives


The main scientific objectives are to:

  • study the seasonal and interannual variability of the upper ocean temperature structure, its heat content and the heat balance in the Southern Ocean
  • understand the dynamics of the different thermal and haline (salinity) fronts
  • quantify the transport and structure of the Antarctic Circumpolar Current
  • study the surface and subsurface salinity, and its relation to the freshwater budget of the Southern Ocean
  • investigate the role of eddies in the Southern Ocean dynamics, and the variations of surface eddy heat, salt and momentum fluxes across the ACC

The SURVOSTRAL project is, based on high density XBT temperature profiles and underway surface thermosalinograph salinity data. The line of repeat observations started in 1992-93, and is called IX28 : an integral part of the CLIVAR project. These observations south of Tasmania are made at one of the three major choke points in the Southern Hemisphere, and measure the inter-ocean exchange between the Pacific and, the Indian Oceans flowing south of Australia.

Systematic launching of high density XBT profiles, reaching a depth of 800 metres, is performed at the beginning, middle and end of each austral summer. XBTs are launched during three return trips of the Astrolabe:

  • R0: mid October – early November : in late spring during the start of the summer heating cycle.
  • R1: December or R2: January, during mid summer.
  • R4: mid February – early March : in late summer, at the start of the autumn cooling.

One or two observers onboard deploy the XBT probes every 2 hours (or every 25 naut. miles or 40 km) from 44°S to 66°S, and every hour in the polar frontal zone from 48°S to 54°S (or every 12 naut. miles or 20 km).

Surface salinity and temperature are recorded continuously using a Seabird Thermosalinograph during all 5 return trips of the ASTROLABE between mid October and early March.

XBT measurements started in October 1992, and thermosalinograph measurements started in October 1993.