Living coccolithophores during the northeast monsoon from the Equatorial Indian Ocean: Implications on hydrography

Abstract

Water samples collected at five stations along 931E section (1 degrees N-4 degrees S) during the northeast monsoon (12-15 February 2000) at five depths (surface, 50, 100, 150 and 200 m) in the eastern equatorial Indian Ocean (EEIO) were studied for coccolithophores. This study has yielded 30 species of coccospheres, showing more diversity compared to coccoliths represented by only 18 taxa. High diversity and abundance of coccospheres were observed at the equator and at 2 degrees S. High concentrations of coccoliths were observed at shallow depths (less than 50 m). The most abundant coccolithophore species was Umbellosphaera irregularis followed by Umbilicosphaera sibogae, Gephyrocapsa oceanica and Emiliania huxleyi. The U. irregularis floral assemblage suggested a prevalence of oligotrophic conditions or lack of supply of nutrients into the upper mixed layer (approx. 50 m thick) during the northeast monsoon. However, the relatively higher abundance of Florisphaera profunda at 4 degrees S indicated the prevalence of nutrient injection into the shallower mixed layer through upwelling from deeper depths.