🦠 Spring Plankton Bloom: Sverdrup Critical Depth, Mixed Layer, Nutrients and Grazing Lab

Follow a year in the upper ocean: astronomical sunlight, a mixed layer that deepens and shoals, Sverdrup's critical depth and a nutrient-phytoplankton-zooplankton model integrated with RK4 decide when the spring bloom starts, peaks and ends. An experiment finds how shallow the summer layer must be, with six independent numerical checks.