Empirical relationships for predicting phytoplanktonic absorption at 6
76 and 436 nm from water column chlorophyll a concentration are presen
ted for distinct geographic regions defined by latitude. The forms of
the predictive equations are controlled by underlying biological mecha
nisms and lend insight into these mechanisms. These region-specific mo
dels allow prediction of phytoplanktonic absorption from more easily m
easured parameters such as chlorophyll a concentration or in situ fluo
rescence and increase accuracy in modeling optical properties or prima
ry production rates from specific absorption coefficients. Phytoplankt
onic absorption can be predicted from chlorophyll a concentrations est
imated from satellite-based ocean color measurements. Temperate and tr
opical regions exhibited statistically indistinguishable relationships
at low chlorophyll so these regions were combined and treated as one.
Nonlinear relationships between phytoplanktonic absorption at both 43
6 and 676 nm and chlorophyll a concentration for the combined temperat
e/tropical region suggested that pigment packaging effects were import
ant and variable. Higher slopes between absorption and chlorophyll a a
t low chlorophyll supported the concept of low pigment packaging effec
ts (thus higher specific absorption) in oligotrophic, low chlorophyll
a waters. Subpolar waters displayed a distinct pattern and were define
d as a separate region. Near-linear and linear relationships between p
hytoplanktonic absorption at 436 and 676 nm and chlorophyll a concentr
ation indicated that influences of pigment packaging on phytoplankton
specific absorption coefficients were relatively constant and uncouple
d from water column chlorophyll a concentration in the subpolar region
. Optical depth correlated inversely with specific absorption at 436 n
m in the subpolar region, illustrating the role of photoadaptation in
determining specific absorption and predictive relationships. Differen
ces between predictive quadratic equations for particulate and phytopl
anktonic absorption indicated that detritus made only a small contribu
tion to the nonlinear nature of the relationships. Absorption by detri
tus at 436 nm ranged from 25 to 90% of the total particulate absorptio
n. The proportion of absorption by detritus did not exhibit any strong
patterns as a function of chlorophyll a concentration, arguing agains
t the previously invoked explanation that proportional increases in ab
sorption by detritus as environments become more oligotrophic cause th
e observed nonlinearity between absorption and chlorophyll a concentra
tion.