CALCULATED QUANTUM YIELD OF PHOTOSYNTHESIS OF PHYTOPLANKTON IN THE MARINE LIGHT-MIXED LAYERS (59-DEGREES-N, 21-DEGREES-W)

The quantum yield phi of photosynthesis (mol C (mol photons)(-1)) was calculated at six depths for the waters of the Marine Light-Mixed Laye r (MLML) cruise of May 1991. As there were photosynthetically availabl e radiation (PAR) but no spectral irradiance measurements for the prim ary production incubations, three ways are presented here for the calc ulation of the absorbed photons (AP) by phytoplankton for the purpose of calculating phi. The first is based on a simple, nonspectral model; the second is based on a nonlinear regression using measured PAR valu es with depth; and the third is derived through remote sensing measure ments. We show that the results of phi calculated using the nonlinear regression method and those using remote sensing are in good agreement with each other, and are consistent with the reported values of other studies, In deep waters, however, the simple nonspectral model may ca use quantum yield values much higher than theoretically possible.