ANALYSIS OF DIEL VARIABILITY IN CHLOROPHYLL FLUORESCENCE

Examples of the diel variability in chlorophyll and beam attenuation a re presented using data from moored in situ fluorometers and transmiss ometers, and from profiles of the beam attenuation coefficient and flu orescence. The data are discussed in terms of the three primary proces ses thought to influence the diel variability in chlorophyll: (I) fluo rescence yield per unit chlorophyll a, (2) chlorophyll a changes per c ell (or, carbon), and (3) changes in phytoplankton carbon (growth). A simple, provisional, model is presented which incorporates these three biological processes, under the assumption that the corresponding die l variability in particle attenuation represents the change in phytopl ankton carbon. The analysis produces qualitative agreement with the in situ data. The model suggests that while under high-light conditions fluorescence declines, chlorophyll can still increase during the day. Under low-light conditions, the diel variability of chlorophyll and fl uorescence are in phase. The model is limited by (I) physiological und erstanding of the processes involved in producing fluorescence and chl orophyll changes over diel time scales; (2) biomass-independent variat ions id particle attenuation; and (3) not including, for the present, physical forcing.