Bio-optical Models of Primary Production
(^) Bio-optical models of primary production (P) take the general form of:
(Eqn. 3.2)
(^) where PAR (mol quanta m−2 s−1) is the photosynthetically available radiation, [Chl-a]
is the chlorophyll-a concentration (mg m−3), a is the Chl-a absorption coefficient
(m^2 [mg Chl-a−1]), and Φc is the quantum efficiency for carbon fixation (mol C[mol
quanta]−1).
(^) Spectral irradiance (PAR) is measured as a function of depth, and variations with
time of day can be calculated from models. Chl-a is measured fluorometrically or by
HPLC of pigments extracted from phytoplankton collected on filters. The absorption
coefficient, a, can be measured from samples collected on filters using a
spectroradiometer. Bannister (1974) proposed an average value of 0.016 m^2 [mg Chl-
a]−1 for a, but more extensive data-sets (Bricaud et al. 1995) show a range of values
(0.18 to 0.01 m^2 [mg Chl-a−1]). The maximum quantum yield (Φc (^) max) of
photosynthesis is determined as:
(Eqn. 3.3)
(^) where αB is the slope of the P vs. E curve, mg C (mg Chl-a)−1 h−1 (μmol quanta m−2 s
−1)−1 determined by the (^14) C method and incubating samples collected from various
depths under a range of light intensities, and is the average chlorophyll-specific
absorption coefficient of phytoplankton weighted by the spectral irradiance inside the
incubation chambers used for determination of the P vs. E curves.
(^) Claustre et al. (2005) used this particular bio-optical model combined with
quantitative information on the composition of the phytoplankton community derived
from HPLC pigment concentrations (Bricaud et al. 2004) to assess phytoplankton
size-specific primary production in the North Atlantic Ocean. The results show that
PBmax, αB, and Φc (^) max all decrease as cell size decreases, but that a, the chlorophyll-a