RELATIONSHIPS BETWEEN ENVIRONMENTAL FORCING AND THE VERTICAL DISTRIBUTION OF CHLOROPHYLL IN THE INDIAN AND PACIFIC OCEANS

The relationships between environmental forcing (hydrographic characteristics of the water column, in situ PAR and major nutrient profiles) and the vertical distribution patterns of in vivo fluorescence and chlorophyll a (Chl a) concentration have been studied along transects of the Malaspina 2010 expedition covering several biogeographic regions in the Indian and Pacific Oceans. Except in the zone of the Equatorial upwelling, a subsurface Chl a maximum (SCM) was generally found at depths between 60 and 150 m. It was typically located at about the 1% light level, in association with the nutriclines and the nitrite maximum. The SCM occurred well below the depth of maximum Brunt-Väisälä frequency in the open Indian Ocean and South Equatorial Pacific, and near or above it in zones strongly influenced by advection (Agulhas, Great Australian Bight). The average proportion of Chl a in the size fraction < 2 micrometers ranged from 60% at surface to 66% at the DCM. The relationship between surface Chl a concentration and integrated Chl a was significant for some geographical regions, but not for the whole data set