A model of annual plankton cycles

A model is presented that exhibits a spring phytoplankton bloom as one feature of a steadily repeating annual cycle of plankton populations. Populations respond to seasonal changes in light (which are gradual) and in mixed layer depth (which may be rapid). The occurrence of a bloom does not require a shallowing of the mixed layer; it does require a low rate of primary production in winter. The lack of phytoplankton blooms in the subarctic...