How can whale poo help fertilise the ocean?

Whale poo fertilises the ocean because whales eat at depth but poo near the surface, which carries nutrients, especially iron and nitrogen, up to where sunlight lets tiny plants grow. This reverses the usual flow of the biological pump, where marine snow and other debris sink from the surface to the bottom. The phenomenon has been termed the whale pump.

The numbers can be startling. Whales transport more nitrogen through their feces in certain regions than all the rivers combined. And the feces of whales are up to 10 million times richer in iron than the surrounding sea water. Iron matters in the Southern Ocean, which is rich in nutrients but short of iron, so whale feces there increase phytoplankton blooms.

A 2010 study of the Gulf of Maine by Joe Roman and James McCarthy estimated that, before commercial culling, nitrogen recycling by marine mammals was three times the supply of nitrogen fixed from the atmosphere. Even today, the local clustering of marine mammals plays a significant role in maintaining productivity where they gather.

It is not only plants that benefit. A study in the Fernando de Noronha Archipelago found that spinner dolphin feces and vomit formed part of the diet of twelve species of reef fish. Several of the large figures come from individual studies, so they are best read as estimates.