JOURNAL OF PLANKTON RESEARCH | VOLUME 5 | NUMBER 6 | PAGES 797-818 | 1983
© Oxford University Press
research-article |
An attempt to simulate the subsurface chlorophyll maximum using populations of unphased oscillating cells
Centre Orstom B.P. A5 Nouméa, New Caledonia
Received on September 1, 1982; accepted on August 1, 1983
A model is proposed to represent the vertical distribution of chlorophyll in tropical waters. It assumes that the phytoplankton populations are composed of cells which oscillate around a mean level at a density 
t = B (close to the nutricline), with an amplitude A; A and B are normally distributed variables; the oscillations are unphased so that the number of cells in a water layer does not vary with the time. This model is tested on data from the eastern tropical Atlantic and from the southwestern tropical Pacific. The results agree with the observations when the surface mixed layer is nutrient-exhausted. However, the model seems to account only for a deep population, and is then consistent with the hypothesis of a distinct mixed layer floral association. The agreement between the results and the observations is difficult when the surface mixed layer is not nutrient-limited, in areas of upwelling or intense vertical mixing. The model accounts for a splitting of the subsurface chlorophyll maximum after the passage of a front in the Cape Lopez area (Guinea Gulf). It also accounts for the relations between the subsurface chlorophyll maximum, the pycnocline, and the nutricline at 48 stations from the cruise PREFIL 2 in the southwestern tropical Pacific. The permanent subsurface chlorophyll maximum of oligotrophic areas seems to be more satisfactorily explained by the unphased oscillations invoked by the model than by the sinking of the cells. These unphased oscillations have not yet been observed; their possible consequences concerning the primary production and grazing are postulated.