S. Agusti et Cm. Duarte, Phytoplankton chlorophyll a distribution and water column stability in thecentral Atlantic Ocean, OCEANOL ACT, 22(2), 1999, pp. 193-203
The relationship between the vertical distribution of phytoplankton chlorop
hyll a and the physical structure of the upper central Atlantic Ocean was i
nvestigated based on results from a cruise across the tropical Atlantic (27
degrees N to 36 degrees S). The thermocline was very sharp and shallow in
the northern part of the transect, off the coast of Mauritania and Senegal,
and deepened progressively to reach > 150 m deep between 20 degrees S and
30 degrees S. There was a deep chl a maximum associated with the thermoclin
e throughout the transect, reaching chl a concentrations up to 50 fold grea
ter than those in surface waters. The chl a concentration was greatest off
the NW African coast and declined towards the south, parallel to a progress
ive deepening of the chl a maximum closely tracking that in the thermocline
. The maximal and the integrated chlorophyll a concentrations varied as the
1/2 and 1/5 power of the surface chl a. The correlation between the depth
where the maximum chl a concentration was observed and the depth where the
thermocline was strongest accounted for 87.2 % of the variance in the depth
of the maximum chl a concentration along the transect. The maximum chl a c
oncentration tends, on average, to be shallower than the depth where the ma
ximal vertical stability is found when the thermocline deepens below 60 m d
epth, and the maximum chl a concentration tended to decline as the depth at
which the Brunt-Vaisala buoyancy frequency was highest increased. Because
the position of the thermocline in the tropical Atlantic Ocean may be predi
cted from climatology, the results reported may be useful to improve the pr
edictions on phytoplankton biomass and production. (C) Elsevier, Paris / If
remer / Cnrs / Ird.