Primary production calculations in the Mid-Atlantic Bight, including effects of phytoplankton community size structure

We developed an absorption-based primary production model that includes the effects of phytoplankton community size structure for the continental margin and adjoining Gulf Stream waters of the Middle Atlantic Bight (MAB). The model uses seasonal cycles of phytoplankton community size structure from previously published results, representative absorption spectra, remotely sensed chlorophyll concentration, sea surface temperature, photosynthetically active radiation, in situ determination of mixed layer dynamics, and previously determined nitrate concentration. The model allows for both light- and nutrient-limitation during the MAB seasonal cycle. Primary production was calculated every month for 5 yr for study areas representing shelf, shelf break, slope, and Gulf Stream waters. Two main approaches were taken to calculate production: using satellite observations integrating to the depth of the mixed layer and using profile observations integrating to the depth of the euphotic zone. The profile euphotic zone production estimates were greater than the satellite mixed layer estimates. Additionally, the timing of production peaks and troughs was largely related to the depth of integration, with profile euphotic zone peak production occurring generally 2 months after the satellite mixed layer estimates. Relative to cell size and seasonality, primary production was regulated more by biomass than light acquisition capability. Comparison of remotely based production estimates and estimates made with in situ depth-dependent data revealed that approximately 30% of daily water column photosynthesis was missed by satellite-based estimates.