absorption coefficient, is highest for the smallest cells (Table 3.2). The latter result is
expected due to the so-called “packaging” effects of chlorophyll in larger cells that
decrease the effective cross-section for absorption of light. The bio-optical approach
to estimating primary production requires simultaneous determination of P vs. E
curves for discrete depths in the euphotic zone, but permits a continuous calculation
of photosynthesis through the euphotic zone based on the rate of light absorption.
Table 3.2 Physiological parameters and phytoplankton biomass variables for modeled
photosynthesis derived from HPLC pigments.
(After Claustre et al. 2005.)
Estimating Primary Production from Satellite-derived
Chlorophyll
(^) In Chapter 2, we described how sensors on various satellites (SeaWiFS, MODIS, etc.)
are used to provide regional and global images of surface chlorophyll concentrations
in the ocean (Plate 2.3). A general correlation between production rates and
chlorophyll standing stocks makes possible a more-or-less convincing estimate of
regional and global primary production rates. Primary production (PP) is the product
of the amount of chlorophyll present in the water column and the efficiency of light
utilization (ε), i.e.:
(^) (Eqn. 3.4)
(^) where C
sat is the satellite-derived estimate of surface chlorophyll, and ε includes the
the Chl-a absorption coefficient (a*) and the quantum yield (Φc) from Eqn. 3.3.
(^) The simplest models of daily net primary production (NPP) incorporate the depth
dependence as follows:
(Eqn. 3.5)
(^) where Pb
opt is the maximum value of Chl-normalized photosynthesis in the water
column (similar to Pbmax); DL is the duration of the photoperiod; Zeu is the depth of
the euphotic zone (depth of 1% surface PAR); and F describes the dependence of
vertically integrated net primary production (ΣNPP) on the surface light intensity as it
affects the depth of light-saturated photosynthesis.