Role of satellites in estimating primary productivity on the northwest Atlantic continental shelf

Variance in primary productivity over the northwest Atlantic continental shelf has been studied to determine its dependence on variables amenable to satellite remote sensing. A large data set consisting of 14C uptake rates, chlorophyll concentrations, incident and underwater light (PAR) and sea surface temperatures was analysed for empirical and theoretical relationships. These data were obtained at 1047 stations surveyed by the National Marine Fisheries Service between 1977 and 1982 as a part of the MARMAP program. Empirically, we found a well-defined seasonal pattern in the ratio of integral productivity to surface layer chlorophyll; its annual maximum occurred in August, lagging the maximum insolation by about 30 days, and coinciding with maximum surface water temperature. The annual minimum occurred during December and January. Surface chlorophyll was highly correlated with mean euphotic chlorophyll concentration ( r 2 = 0.93 ) and moderately correlated with mean euphotic productivity ( r 2 = 0.62 ). Theoretical models of the dependence of integral productivity on chlorophyll and light were considered. It was found that parameters in such models can be highly variable, in particular those that characterize light absorption characteristics of the phytoplankton. We conclude that the goal of estimating primary productivity from satellite measurements requires improved techniques for measuring and/or modeling the PAR absorbed by photosynthetic organisms.