The tropical ocean off the west coast of South America has several unusual attributes.
The upwelling cool waters of the Humboldt Current System that controls it is surprisingly cool for an ocean so close to the equator. This shows how strong the upwelling is that is bringing nutrients up to the light where they can contribute to the generation of microscopic plant life: the phytoplankton.
As a result of this enhanced productivity, the northern Humboldt Current off Peru produces more fish per unit area than any other region of comparable area in the world’s oceans.
Because the extraordinarily abundant surface life removes much of the oxygen from surface waters, there is a stratum of shallow water just below the surface that is low in oxygen. It’s called the Oxygen Minimum Zone or OMZ. It’s where oxygen is so depleted that many life forms can’t survive in it. There are, nevertheless, a variety of creatures that have adapted to use less oxygen and for them the Oxygen Minimum Zone is a refuge from predators. However, because whales can hold their breath for so long, they are able to exploit these creatures while swimming through the Oxygen Minimum Zone and capturing the life that has evolved to survive such conditions. This means that the Oxygen Minimum Zone represents a barrier for smaller animals that live above it, and that factor crams a lot more life into the near-surface waters.