The University of Maine Maine In-situ Sound & Color Lab
School of Marine Sciences
Carbon-Based Net Primary Production and Phytoplankton Growth Rates from Ocean Color Measurements: Part II

Historically, net primary production (NPP) has been modeled as a function of chlorophyll concentration, allowing for a natural application to ocean color satellite data. However, cellular chlorophyll content is highly variable and is affected by photoacclimation and nutrient stress which act to confound global NPP model results. An approach to accommodate these limitations was recently introduced providing satellite NPP estimates based on backscattering-phytoplankton carbon relationships and mixed layer phytoplankton growth rates (ų, divisions per day) derived from chlorophyll:carbon ratios. This initial Carbon Based Productivity Model (CBPM) made many assumptions about the underwater light field, photoacclimation, and the application of satellite physiological data for estimating water column NPP. Here, we re-evaluate these initial treatments and their influence on CBPM estimates of global ocean NPP. Estimation of full vertical profiles of ų can be calculated given knowledge of the surface mixed layer depth and the nitracline depth, which allow appropriate parameterization of photoacclimation and nutrient stress through the water column. In addition, accounting for the spectral attenuation of the light field with depth yields more realistic mixed layer irradiances and euphotic depths. Preliminary results indicate that estimated NPP rates are highly sensitive to these changes, resulting in global annual NPP differences greater than 10 Pg C yr-1. It is shown that these calculations can be made entirely based on satellite remote sensing measurements and climatological mean fields giving the ability to imply global patterns in phytoplankton physiological indices which are broadly consistent with laboratory-based studies. Direct validation using regional in situ datasets of phytoplankton chlorophyll:carbon, cellular growth rates, and measured NPP rates support the findings presented here.

Westberry, T.K., M.J. Behrenfeld, E. Boss, and D.A. Siegel, 2006. Carbon-Based Net Primary Production and Phytoplankton Growth Rates from Ocean Color Measurements: Part II. 2006 Spring Ocean Sciences Meeting.

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