More realism can be obtained by letting some of the phytoplankton and zooplankton
that die (–m P − k Z) “sink”, and by mixing nutrient-rich (10.6 μM) deep water
into the upper layer with corresponding removal of upper-layer water (with nutrients
and phytoplankton), both at a rate of 2% of upper-layer water daily. Also, an autumn
(fall) bloom can be added by increasing the mixing rate from some arbitrary day
onward, shown as day 120, at 2% per day. All of these changes are specified in
program comments (Box 4.3). The result (Fig. 4.4d) has a large, if too brief, spring
bloom, low summer standing stocks, and a fall bloom not quite half as strong as that
in spring. Nutrients then rapidly return to initial levels and the fall bloom is removed
by increased mixing and grazing.
A (Somewhat) More Complex NPZ Model
(^) That Franks et al. (1986) model has evoked a great deal of analysis (e.g. Busenberg et
al. 1990; Edwards et al. 2000), but it is not realistic in several respects, apart from the
extreme simplification of its biological variables relative to the complexity of an
actual pelagic community. Most importantly, we understand that blooms are initiated