SECTION 2. PRESENT LIMITATIONS 



Space and time domains of the relevant biological and physical processes 

 controlling productivity are compared in Figure 2-1 with the present 

 space-time sampling regimes of various measurement platforms. Individual 

 phytoplankton, zooplankton, and fish have life cycles on the order of 

 respectively 1 cycle day" , 0.1-0.01 cycles day" , and 0.01-0.001 cycles 

 day" (Walsh et. al., 1977), which are translated into longer time scales 

 of the communities within which their birth and death processes take place. 

 Phytoplankton communities, for example, experience major changes over 

 periods on the order of 1 to 10 days and, as a result of shelf flow regimes, 



over areas of 10 to 100 square kilometers. Fish, because they are larger, 



2 3 

 swim faster and live longer, occupy the time domain between 10 to 10 



days and the space domain between 10 to 10 square kilometers. Comparing 



these domains for various physical processes and resultant biological 



distributions with the sampling regimes of the various measurement 



platforms (Table 2-1), one arrives at a major reason for the proposed MAREX 



program--the need to measure distributions of biological properties at 



frequencies which can resolve causally the sources of their variance. 



2.1 SHIP IN SITU SENSING 



Classical shipboard programs consist of productivity measurements made 

 once a day over a spatial area limited by the usual 10-12 knot speed of the 

 research vessel. At present, shipboard rate measurements, such as 

 nutrient uptake, photosynthesis, respiration, grazing, excretion, and 

 sinking, can only be made at a few points of the sea, to be later multi- 

 plied by some inadequate estimate of mean biomass in order to calculate 

 fluxes of elements within the marine food web. However, phytoplankton 

 species on the continental shelves can divide every 0.5 to 2 days; without 

 losses, a population during the spring bloom could increase at the same 

 rate. To resolve the temporal and spatial consequences of this resultant 

 rate process, a sampling frequency of at least 0.25 day" is required by 

 sampling theory (Blackman and Tukey, 1957). 



2-1 



