The EQUALANT program (PI : C.Andrié -IRD, ex ORSTOM-) is a component of the ECLAT (Etudes CLimatiques dans l'Atlantique Tropical) program, French component of the international CLIVAR (CLImate VARiability and predictability) program in the tropical Atlantic. One of the main objectives of this programme is the study of the ocean circulation variability and the ocean-atmosphere interactions in the equatorial Atlantic.

The EQUALANT 99 cruise (PIs: C.Andrié and Y.Gouriou -IRD-) will take place in boreal summer 1999 during 42 days (July, 12 to August, 22) on board the R/V THALASSA, from Salvador de Bahia (Brazil) to Abidjan (Ivory Coast). It consists on carrying out hydrology (CTDO₂), currents (VMADCP, LADCP), tracers (nutrients, CO₂ system parameters, CFCs), and primary production parameters measurements along three meridional sections from 6°S to 6°N at 35°W, 22°W, 10°W and along one zonal section at 8°S in the westernmost part of the basin (see map below). XBT and XCTD (0-1000 m) probes will be launched every ¼° during transits and sometimes between casts. Along with these oceanographic measurements, meteorological parameters (temperature, wind, solar fluxes…) will be also measured thanks to an instrumented mast located on the foredeck of the vessel. Sounding balloons will be released during the stations carried out around 0h and 12h TU. 36 hours stations will be done at some PIRATA buoys locations (35°W-Equator, 10°W-Equator and 10°W-2°N), in order to assess turbulent fluxes at the sea-air interface and to improve their parameterizations. During these stations, repeated profiles (CTDO₂, LADCP) will be carried out. Along 10°W, 16 SVP drifting buoys (given by NOAA/AOML) will be launched, along with one 'CARIOCA' buoy (pCO₂ measurements).

At the time of the cruise, four moorings will be deployed (PI: C. Provost -LODYC-) between 0°50'S and 0°50'N along 10°W in July 1999 from the R/V ANTEA. These moorings will record hydrological (temperature, salinity) and current measurements continuously (ADCP and Yoyo system) in the first 1000 m depth at the equator (location of a PIRATA buoy), and current measurements between 1000 and 2000 m at the equator, 0°50'S and 0°50'N, in order to assess the characteristics of the deep equatorial jets.

A second cruise (EQUALANT 2000; PIs: C.Andrié and B.Bourlès -IRD-) is planed in August-September 2000, in order to complete the survey of the Atlantic basin, east of 10°W. During this cruise, hydrographic, current and tracer measurements will be done along three meridional sections across the equator, between the African continent and 10°W, common section to both cruises. The four moorings will be recovered during this cruise.

Equalant 1999 cruise trackline (blue) with CTD casts location (blue dots),

along with location of the PIRATA buoys (black dots).