OISO cruises have been conducted in the South Indian Ocean and corresponding Antarctic sector since 1998 onboard the R.V. Marion-Dufresne (French Polar Institute) in the frame of the long-term observational CARAUS program (INSU/IPSL).The objective is to monitor and understand the seasonal, interannual and decadal variations of the oceanic carbon cycle.
 
The dataset consists of 6 cruises (OISO1-6) conducted between 1998 and 2001 along repeated lines between La Réunion Island (21°S, 55°E), Crozet (46°S, 52°E), Kerguelen (49°S, 69°E) and Amsterdam (39°S, 77°E) during austral summer and winter. During each cruise, up to 19 CTD stations are performed (1 cast with 24 bottles, except for station 11 performed in 2 casts). Samples are collected down to 1000m, except for 3 stations performed down to the bottom (stations 10, 11 and 17). (Note that station 10 is located at the KERFIX time-series site).

Measured Parameters
  -  Parameters in station files: 
pressure, CTD temperature, CTD salinity, measured salinity, CTD oxygen, measured oxygen, potential temperature (theta), potential density (sigma-0), alkalinity, dissolved inorganic carbon, silicate, nitrate, chlorophylle-a.
  -  Other station data: 
13C, 18O (during OISO6: bacteria/phytoplankton).
  -  Underway measurements (surface):
temperature, salinity, pCO2, alkalinity, dissolved inorganic carbon, nitrate, silicate, chlorophylle-a, 13C and 18O.
  -  Atmospheric measurements:
CO2, 13C, 18O (since 2000: + CH4 and NO).