THE DISTRIBUTION OF BIOLUMINESCENCE AND CHLOROPHYLL DURING THE LATE SUMMER IN THE NORTH-ATLANTIC - MAPS AND A PREDICTIVE MODEL

During August 1991 an instrument array (the Paravane) was towed contin uously for several days over long distances in the North Atlantic and around the Marine Light-Mixed Layer (MLML) mooring (60 degrees N, 21 d egrees W). Among other sensors, the Paravane carried a thermistor, a f luorometer that measured the fluorescence emitted by chlorophyll a, a bathyphotometer that measured stimulable bioluminescence, and a beam t ransmissometer that measured the volume attenuation coefficient at 490 nm. The record of these biooptical measurements provides a detailed d escription of the upper 150 m of the water column as well as of diel v ariability. An examination of the transects, which covered a latitudin al range from 43 degrees N to 60 degrees N and a longitudinal range fr om 13 degrees W to 54 degrees W, indicates that in the colder and more northerly waters most of the chlorophyll a, attenuation, and biolumin escence were found within the surface mixed layer, In the warmer water s to the south, there were subsurface maxima for all three parameters. We have used the Paravane records to test a model that provides predi ctions of the vertical distribution of chlorophyll a, bioluminescence, and beam attenuation from oceanographic parameters that characterize the surface mixed layer: temperature, chlorophyll a concentration, irr adiance incident to the sea surface, mixed layer depth, and nitrate co ncentration. The first three parameters can be measured from sensors a board satellites while the last two parameters can be obtained from oc eanographic databases. The model is based upon a description of the ac climation of the phytoplankton, an assumption about the vertical distr ibution of phytoplankton within the euphotic zone, and an empirical de scription of the relationship between bioluminescence, light intensity , and phytoplankton concentration.