## Abstract

By use of a common primary-production model and identical photosynthetic parameters, four different methods were used to calculate quanta (*Q*) and primary production (*P*) at depth for a study of high-latitude North Atlantic waters. The differences among the four methods relate to the use of pigment information in the upper water column. Methods 1 and 2 use pigment biomass (*B*) as an input and a subtropical, empirical relation between *K _{d}* (diffuse attenuation coefficient) and

*B*to estimate

*Q*at depth. Method 1 uses measured

*B*, but Method 2 uses

*B*derived from the Coastal Zone Color Scanner (subtropical algorithm) as inputs. Methods 3 and 4 use the phytoplankton absorption coefficient (

*a*

_{ph}) instead of

*B*as input, and Method 3 uses empirically derived

*a*

_{ph}(440) and

*K*values, and Method 4 uses analytically derived

_{d}*a*

_{ph}(440) and

*a*(total absorption coefficient) values based on the same remote measurements as Method 2. When the calculated and the measured values of

*Q*(

*z*) and

*P*(

*z*) were compared, Method 4 provided the closest results [for

*P*(

*z*),

*r*

^{2}= 0.95 (

*n*= 24), and for

*Q*(

*z*),

*r*

^{2}= 0.92 (

*n*= 11)]. Method 1 yielded the worst results [for

*P*(

*z*),

*r*

^{2}= 0.56 and for

*Q*(

*z*),

*r*

^{2}= 0.81]. These results indicate that one of the greatest uncertainties in the remote estimation of

*P*can come from a potential mismatch of the pigment-specific absorption coefficient (

*a*

_{ph}*), which is needed implicitly in current models or algorithms based on

*B*. We point out that this potential mismatch can be avoided if we arrange the models or algorithms so that they are based on the pigment absorption coefficient (

*a*

_{ph}). Thus, except for the accuracy of the photosynthetic parameters and the above-surface light intensity, the accuracy of the remote estimation of

*P*depends on how accurately

*a*

_{ph}can be estimated, but not how accurately

*B*can be estimated. Also, methods to derive

*a*

_{ph}empirically and analytically from remotely sensed data are introduced. Curiously, combined application of subtropical algorithms for both

*B*and

*K*to subarctic waters apparently compensates to some extent for effects that are due to their similar and implicit pigment-specific absorption coefficients for the calculation of

_{d}*Q*(

*z*).

© 1996 Optical Society of America

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