Keep in mind that the current growth function does not account for nutrients, which may slow down the growth outside the plume. The current growth rates are based on data from nutrient replete environments. Temperature severely limits growth rate throughout the first half of the run. It seems to be the predominant limitation at the surface where most of the growth takes place. The light is undoubtedly more limiting at depth, but there are also less cells at depth due to the tendency of A. tamarense to migrate to the surface.
Light also bring growth to a practical stand still at night.