The geological stroke of luck that protects marine life in the Galapagos

This story originally appears in The same review and is part of the Climate office collaboration.

Driven by climate change, almost all parts of the ocean are warming. But off the west coast of the Galapagos Islands there is an area of ​​cold, nutrient-rich water. This thriving patch feeds phytoplankton and breathes life into the archipelago.

“Cool water supports populations of penguins, marine iguanas, sea lions, fur seals and cetaceans that could not stay on the equator all year round,” says Judith Denkinger, marine ecologist at San Francisco University in Quito, Ecuador. .

Over the past four decades, this cold zone has cooled by about half a degree. Its persistence has scientists wondering how long it will last. The Galapagos Islands are already renowned for their biodiversity. Could the open waters become a refuge for marine animals seeking cold water in a warming world? The answer, it seems, is yes. At least for a moment.

There are other cold pools on the planet. One, in the North Atlantic just south of Greenland, is caused by the weakening of a global current that carries heat north. But according to a new study led by Kris Karnauskas and Donata Giglio, climatologists at the University of Colorado at Boulder, the Galapagos cold pool is the product of the shape of the sea floor and the rotation of the planet – two things that won’t change. probably not because of rising greenhouse gases. And the Galapagos aren’t the only islands seeing this effect.

Along the equator, several islands have exceptionally cold water located immediately to their west. According to the work of Karnauskas and Giglio, this cooling is the product of an upwelling caused by the collision of a deep ocean current against the islands in its path.

By analyzing 22 years of ocean temperature data collected by Argo floats, as well as observations from satellites, ocean gliders and cruise ships, scientists constructed temperature profiles around several equatorial islands and identified the location of the Equatorial Underwater Current (EUC), a cold, fast current that moves eastward about 100 meters below the surface of the Pacific Ocean. The EUC is held in place along the equator by the Coriolis force, an inertia caused by the rotation of the Earth on its axis. This same effect twists hurricanes counter-clockwise north of the equator and clockwise south of it.

Work from Karnauskas and Giglio shows that when EUC comes within 100 kilometers west of the Galapagos Islands, it suddenly intensifies as it is deflected upward by the islands. This makes the water up to 1.5 degrees Celsius cooler than the water outside this cold pool. The researchers found a similar, but weaker, effect west of the Gilbert Islands in the western Pacific Ocean.

In a separate study, Karnauskas shows that over the past few decades the EUC has grown stronger and deeper. It also moved about 10 kilometers to the south, further aligning its path with the Galapagos Islands. All of these changes contribute to the observed cooling, Karnauskas says.

For the Galapagos marine ecosystem, this cooling is “a bit mixed,” says Jon Witman, a marine ecologist at Brown University in Rhode Island who was not involved in the studies. “The fresh upwelling water from EUC certainly has significant positive impacts,” he says. But when combined with other ocean processes that also cause temperatures to drop, such as La Niña, the cooling can harm some wildlife, such as by shocking corals, causing them to bleach and sometimes die.

In the near future, this cold shield will likely benefit life around the Galapagos Islands and other equatorial islands. But that cooling water is fighting a losing battle with a warming atmosphere, Karnauskas says. “This cooling trend will probably not last the whole century; it will eventually be overwhelmed,” he says.

If some species are protected at least for a while, however, the Galapagos could become a gene bank that could be used to reseed devastated marine ecosystems elsewhere, suggests Karnauskas. “And it’s just beautiful that this is the iconic Galapagos that we’re talking about here.”