The adaptability of the Galápagos Islands’ animals famously stimulated Charles Darwin’s thoughts, leading to one of the great scientific revolutions. Scientists have been studying the islands intensively ever since. One question that has puzzled them may finally have been solved: the source of the biological richness that so inspired Darwin.

Neither the islands’ steep rocky uplands nor the modest rainfall closer to sea level is conducive to the abundant plant life that forms the base of the food chain on other tropical islands. Instead, the Galápagos’ organic wealth comes from the sea. Nutrient-rich bottom waters well up around the islands at certain times of the year, driving explosive phytoplankton growth. The center of the upwelling was once home to so many whales it was referred to as the “mother load” on its discovery. The islands are close enough the waters around them are rich in fish, on which the islands’ birds, seals, and iguanas prey.

The mystery has been why the upwellings occur at such a convenient location – Darwin’s work having discredited the idea a benevolent creator decided to bestow a gift on the islands. In the 1960s, oceanographers proposed the Equatorial Undercurrent brings nutrients to the surface when it runs into the islands. The Undercurrent flows east around 100 meters (330 feet) beneath the surface, opposite to the Coriolis-driven currents to the north and south.

Professor Alberto Garabato of the University of Southampton, UK noted there are few observations of how the Undercurrent interacts with the islands, and suspected there must be more to the story. Rich as these waters are, they experience extreme fluctuations, particularly marked by sharp falls in phytoplankton density during El Niño events.

Garabato and colleagues noted upwelling intensity correlates with the seasonal strength of the region’s predominant winds, which flow mostly north and a little west. They sought a causal connection and in a paper published in Scientific Reports explain how these winds create turbulence in the regions’ oceans, allowing nutrient-rich cold waters to rise to the surface.

This instability is marked by sharp contrasts in water temperature known as upper-ocean fronts, which resemble smaller versions of the cold fronts seen on weather maps in association with storms.

The islands are surrounded by one of the world’s great marine parks, but dark fishing fleets are wreaking havoc just outside the protected waters, and are suspected of straying within.

"This new knowledge of where and how the injection of deep-ocean nutrients to the Galapagos ecosystem happens is informing ongoing plans to expand the Galápagos Marine Reserve, and improve its management against the mounting pressures of climate change and human exploitation," Garabato said in a statement. A better understanding of the causes of the upwelling could improve predictions of the timing of events and the surges in life that follow.