the light-limited reaction, which is temperature independent. Figure 4- 

 2 shows an Arrhenius plot for temperature dependence of P m ; the dramatic 

 decrease in photosynthesis at extremely high temperatures depicts high- 

 temperature inactivation of enzyme activity. The genetic composition of 

 the phytoplankton assemblage in a subregion of the ocean will affect the 

 specification of a particular environmental effect, but the general 

 functional form and direction (sign) of an environmental effect is 

 universal. Information on temperature will thus provide empirical 

 limits for primary productivity. Simultaneous remote sensing of ocean 

 temperature will obviously increase the accuracy and precision of 

 remotely sensed primary productivity estimates. 



Nutrient availability, specifically of nitrogen, modulates primary 

 production in two ways: a lack of nitrogen causes a decrease in 

 chlorophyll concentration per cell and, hence, decreases the potential 

 of a phytoplankton assemblage to increase in biomass; nitrogen limita- 

 tion also causes a decrease in the efficiency of both a and P for the 

 persisting chlorophyll. In some U.S. coastal areas dominated by 

 upwelling events (Table 4-1) and in open ocean regimes with strongly 

 divergent circulation, surface temperature is highly correlated with 

 nutrient concentration. Figure 4-3 shows a relationship between surface 

 temperature and nitrate in 10° longitudinal bands along the west coast 

 of North and South America. For these regions the empirical relation- 

 ship between low surface temperature and high nutrient provide limits 

 for specifying the magnitude of the nutrient modulation of primary pro- 

 ductivity. In other regions of coastal outwelling, shipboard infor- 

 mation on nutrient inputs will still be required in conjunction with 

 salinity information from aircraft over flights; within the next decade 

 it may be feasible to measure nutrients from mrored sensors as well, 

 e.g., with specific ion electrodes, lasers, or wet chemistries. 



Vertical mixing in the upper ocean affects the distribution of 



phytoplankton in context of both nutrient resupply and the vertical 



light intensity gradient. Vertical mixing thus has an additional impact 



on primary production by determining the amount of time that a cell 



resides at light intensities greater than I (e.g., P ) and at 



intensities less than I (a) . Figure 4-4 shows the results of a Markov 



m 3 



4-9 



