Equatorial Undercurrent Could Explain Galápagos Islands' Unique Biodiversity

The Galápagos Islands are well known for their biodiversity, housing plants, and animals that aren't found anywhere else on earth. For years, scientists have been trying to figure out the origin and time frame of this phenomenon and at last, a study published in Earth and Planetary Science Letters has the answer.

Cooperative Institute for Research in Environmental Sciences Fellow Kris Karnauskas, the lead author of the study, proposed that the geologic formation of one particular part of the archipelago that formed around 1.6 million years ago could be responsible for the Galápagos Islands' unique biodiversity. Despite authoring six peer-reviewed scientific papers on the Galápagos Islands, Karnauskas still hadn't found the answer to when biodiversity flourished in the Galápagos.

"I asked around and couldn't get a straightforward answer," said Karnauskas, an assistant professor in the Department of Atmospheric and Oceanic Sciences at the University of Colorado Boulder. "My geology friends said anywhere between half a million to twenty million years ago, depending on what feature we're talking about."

To determine exactly when the Galápagos turned into one of the most biologically diverse places on earth, Karnauskas looked beyond the age of the Galápagos islands. "I wasn't really interested in when the very first island breached the surface, but when this ecosystem developed," Karnauskas recounted. "That's not the customary way to ask questions in geology, nor does it lend itself to the usual toolbox."

Karnauskas proposed that the Equatorial Undercurrent (EUC) colliding with the archipelago caused the biological explosion in the Galápagos. Due to the shape of Earth and the way it spins, the EUC remains at the equator. In the case of the Galápagos, islands emerged from the seafloor and blocked the current. The island of Isabela in particular interested Karnauskas. "It's a pure accident of geography that Isla Isabela is so large and stands right on the equator, right where the EUC is trying to pass through. This is enough to drive cold, nutrient-rich water up to the surface where it can fuel marine productivity. We can easily see it today from space; the water is very cold and productive just west of the Galápagos along the shores of Isabela. It's no surprise that you'll find all the penguins jumping in the water there."

Karnauskas and his colleagues used previously collected data from sediment cores pulled up from sample sites near the Galápagos Islands. They noticed that around 1.6 million years ago, changes in the chemical composition of the fossil bugs in the sediment suggested a marked change in temperature.

Since the EUC could no longer flow to the mainland, this resulted in diversifying the species of fish, plants and penguins in the Galápagos. "Typically, we use known geologic constraints to help explain past changes in the environment such as ocean circulation," says Karnauskas. "It contributes a unique data point not only for geology but also for ecology and biogeography -- where and when life is distributed."