During August 1991 an instrument array (the Paravane) was towed continuously for several days over long distances in the North Atlantic and around the Marine Light-Mixed Layer (MLML) mooring (60 ¿N, 21¿W). Among other sensors, the Paravane carried a thermistor, a fluorometer that measured the fluorescence emitted by chlorophyll a, a bathyphotometer that measured stimulable bioluminescence, and a beam transmissometer that measured the volume attenuation coefficient at 490 nm. The record of these bio-optical measurements provides a detailed description of the upper 150 m of the water column as well as of diel variability. An examination of the transects, which covered a latitudinal range from 43 ¿N to 60 ¿N and a longitudinal range from 13 ¿W to 54 ¿W, indicates that in the colder and more northerly waters most of the chlorophyll a, attenuation, and bioluminescence were found within the surface mixed layer. In the warmer waters to the south, there were subsurface maxima for all three parameters. We have used the Paravane records to test a model that provides predictions of the vertical distribution of chlorophyll a, bioluminescence, and beam attenuation from oceanographic parameters that characterize the surface mixed layer: temperature, chlorophyll a concentration, irradiance incident to the sea surface, mixed layer depth, and nitrate concentration. The first three parameters can be measured from sensors aboard satellites while the last two parameters can be obtained from oceanographic databases. The model is based upon a description of the acclimation of the phytoplankton, an assumption about the vertical distribution of phytoplankton within the euphotic zone, and an empirical description of the relationship between bioluminescence, light intensity, and phytoplankton concentration. ¿ American Geophysics Union 1995