photosynthetic rates, now make feasible the extrapolation of rates of 

 primary production, with confidence limits, from shelf phytoplankton 

 biomass . The most commonly used measure in oceanography of 

 phytoplankton biomass is chlorophyll a_ concentration. The photosynthetic 

 process, the basis of primary production can be specified by 



n(C0 2 ) + 2n(H 2 0) _ _ J L 9 .!?!: _ _ _>. n (CH 2 0) + n(0 2 ) + n(H 2 0) 



Chlorophyll a 



where C0 ? is carbon dioxide, HLO is water, (CH 2 0) represents a primary 

 unit of photosynthetically fixed organic carbon, and CU is molecular 

 oxygen. Photosynthesis is comprised of two basic components: a photo- 

 chemical (or so-called light) reaction in which light energy is trapped 

 by chlorophyll and converted into biochemical reducing potential; and an 

 enzymatic (or so-called dark) reaction in which the biochemical reducing 

 potential is used to synthesize organic carbon. 



The process of photosynthesis is characterized by a three parameter 

 functional response to light intensity (Figure 4-1) where a describes 

 the light-limited photochemical portion of the reaction, P describes 

 the light-saturation or enzyme rate-limited portion, and 3 describes a 

 photo-inhibition effect experienced at very high light intensities. 



photosynthesis 

 per unit 

 chlorophyll a_ 



light intensity 

 Figure 4-1. Functional Response of Photosynthesis to Light Intensity 



Recently, theoretical upper limits have been determined for the two major 

 components of photosynthesis: a and P . Both parameters can be 

 specified as functions of chlorophyll a_ with a as carbon fixed per 

 chlorophyll a_ per unit light intensity per time, and P as a maximal 

 rate of carbon fixed per chlorophyll per time. Based on the well- 

 specified maxima quantum yield (amounts of energy fixed in carbon bonds 

 per quantum of light energy absorbed by chlorophyll), the theoretical 



4-7 



