The Blue Machine

Phytoplankton are a diverse, complex and beautiful group of organisms, but their major needs are quite simple. They need sunlight, nutrients, carbon dioxide and water, although this last one has never yet been considered a limiting factor in the ocean. It’s the first two that hold things back. The upper (generally warm) layer of the ocean has plenty of sunlight. But nutrients there can get used up quite quickly. Down in the deeper, colder water hidden beneath, there tends to be plenty of nutrients, but no sunlight. Tiny single-celled phytoplankton are capable of a truly monumental task: building the foundation of the entire ocean food chain. But they can only do this when both light and nutrients are present–both the energy and the raw material–and our layered ocean tends to keep these critical ingredients frustratingly separate: light up top, nutrition down below. The cold current noted by von Humboldt (and later named after him) is the site of a very effective solution to this fundamental problem.