Seasonal and geographic variations in phytoplankton losses from the mixed layer on the Northwest Atlantic Shelf

The total daily phytoplankton loss from the mixed layer is estimated as the difference between the primary production and the realized change of phytoplankton carbon biomass. A Monte Carlo procedure is used to recover the total loss rates for ten geographic locations on the Northwest Atlantic continental shelf. The strong seasonal and geographic variations in mixed-layer loss rates of phytoplankton are tied closely to the primary production. The daily, mixed-layer, total loss ranges from 50 to 1000 mg C m− 2 d− 1, which is compared with the output of process models, the closure error being generally less than 10% of the total loss. The model results show that the annual respiration is generally greater than losses due to zooplankton grazing and sinking, except that zooplankton grazing dominates other loss terms on the west Greenland shelf.