Why are cold ocean waters more “nutrient-rich” than tropical waters?
It’s fairly complicated, but in simple terms it’s because warm water rises and cold water sinks. The problem with nutrients in the ocean is that they are accumulated in the bodies of living things, and living things are solid, and solid objects tend to sink. A fish carcasse or a plankton carcasse might gloat for a few hours or a few days, but then it sinks. And it sinks straight to the bottom of the ocean, carrying all the nutrients it concentrated in its lifetime with it. As a result upper level ocean waters tend to become nutrient depleted very quickly. Even if I spray fertiliser on the ocean to increase the nutrient levels I will only get a brief bloom of life, and then it will die… and sink straight to the bottom. Dead things like logs or wildebeest lie around on the surface on the land, and so the nutrient they accumulated can be released by decay and used all over again by other lifeforms. So you get localised nutrient cycling on the land. Living things in the ocean sink, so any
