A submersible pump and a continuous flow fluorometer were used to obtain the vertical pH and fluorescence profiles from the top 140 m of the seawater in the region between La Reunion, Seychelles and Djibouti in the western tropical Indian Ocean during the 1986 INDIGO 2 Expedition. The calculated chlorophyll a maxima are generally located near the nutracline, all within 50 m of the surface mixed layer and closer to the mixed layer at night but deeper in daytime. The chlorophyll a concentration in the mixed layer is uncorrelated with the concentration at the chlorophyll a maxima but is correlated with the integrated amount from surface to 116 m.
Continuous salinity, temperature and oxygen data from a CTD probe, and pH data from discrete samples collected by the submersible pump and by Rosette bottles are compared with the chlorophyll α profile.