The below movie displays the biological response to a wind-driven upwelling event in a coastal ocean. Two classes of plankton are represented. Phytoplankton (the plants) and zooplankton (the animals). The phytoplankton multiply best in warm, sunlight water with lots of nutrients. Zooplankton multiply best in warm turbulent water, with lot of phytoplankton to eat. Of course, the phytoplankton population is reduced by zooplankton eating them. In turn, the nutrients are decreased by the multiplying phytoplankton.

First, the model uses lots of physical equations to determine how the water responds to wind. The nutrients, phytoplankton and zooplankton populations are moved around by this water motion. At the same time, equations representing the phytoplankton growing, zooplankton eating and phytoplankton being eaten change the populations as well. The combination of physical and biological processes results in the changing concentrations you see ...
 
 

Plot details: The plots show temperature (T, [^oC] ), alongshore (into the screeen) velocity (v,[m s ^-1]), the streamfunction (flow occurs along lines), dissipation of turbulent kinetic energy (epsilon (e), [m s^-1]),  sunlight (I, [mol photons m² s^-1 ]), nitrate concentration (N, [mol N m^-3]), phytoplankton concentration (P, [mol N m^-3]), and zooplankton concentration (Z, [mol N m^-3]). The plot shows only the surface east component of the model domain.

Commentary: The model has been run from Day 304 (November 1, austral spring) for one year with a sinusoidally varying wind stress. This sets up a relatively constant physical environment. One year provides time for the biological components of the model to reach a quasi steady-state. At Day 669, an upwelling event is driven by a constant 0.05 N m^-2 wind stress . The temperature field shows upwelled water on the west coast of a basin. The nutrient-rich, phytoplankton-poor bottom water is brought to the surface where there is plenty of light. Once it reaches the surface it is advected eastward. In this eastward current,  nutrient-enriched, sun-bathed phytoplankton cells bloom. By Day 700, phytoplankton in the surface coastal waters have bloomed. Watch the light field change as the blooming phytoplankton absorb light. Although the bloom appears relatively stationery, infact it is being advected westward at up to 2 km per day. But the as the bloom reaches about 30 km west of the coast, zooplankton grazing becomes sufficient to remove the deplete the phytoplankton. Of course, the zooplankton themselves are being advected westward, but their loss to the west is balance by their quick growth in the presence of lots of food (the phytoplankton).

Simulation details: Physical fields are modelling using the Princeton Ocean Model. The biological response is modelled using a modified version of Baird and Emsley (1999). More details will follow.

Whole domain: What of the rest of the ocean basin. The second plot shows the whole model domain. Look at the behaviour in the west coast. Instead of upwelling, the water is sinking. Can you explain the biological response ?