Driven by climate change, almost every part of the ocean is warming. But on the west coast of the Galapagos Islands, there is a patch of cold, nutrient-rich water. This rich patch feeds the phytoplankton and gives life to the archipelago. “The cool water sustains populations of penguins, marine iguanas, sea lions, seals and cetaceans that could not remain at the equator year-round,” says Judith Denkinger, a marine ecologist at the Universidad San Francisco de Quito in Ecuador. . Over the past four decades, this cold patch has cooled by about half a degree. Its persistence has scientists wondering how long it will last. The Galapagos Islands are already famous for their biodiversity. Could open sea water become a refuge for marine animals seeking cold water in a warming world? The answer, it seems, is yes. At least for a while. 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 transports heat north. But according to a new study led by Kris Karnauskas and Donata Giglio, climate scientists at the University of Colorado Boulder, the Galapagos cold pool is a product of the shape of the seafloor and the planet’s rotation — two things unlikely to change due to increased of greenhouse gases. And the Galapagos aren’t the only islands to see this phenomenon. Along the equator, many islands have unusually cold water immediately west of them. According to the work of Karnauskas and Giglio, this cooling is the product of upwelling caused by the collision of a deep ocean current with the islands in its wake. By analyzing 22 years of ocean temperature data collected by Argo floats, along with observations from satellites, ocean gliders and cruise ships, scientists constructed temperature profiles around several equatorial islands and pinpointed the location of the Equatorial Overcurrent (EUC), a cold, fast-flowing current traveling 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 phenomenon twists hurricanes counterclockwise north of the equator and clockwise south of it. Karnauskas and Giglio’s work shows that when the EUC reaches within 100 km west of the Galapagos Islands, it suddenly intensifies as it is deflected up from the islands. This results in the water being up to 1.5 °C 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 in recent decades, the EUC has been getting deeper and deeper. It has also moved about 10 kilometers south, aligning its path more 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 of a mixed bag,” says Jon Witman, a marine ecologist at Brown University in Rhode Island, who was not involved in the studies. “EUC’s cool water definitely has significant positive effects,” he says. But when combined with other oceanic processes that also cause temperatures to drop, such as La Niña, the cooling can harm some wildlife, such as cold-shocked corals, causing them to bleach and sometimes die. For the foreseeable future, this cold shield will likely benefit life around the Galapagos Islands and other Ecuadorian islands. But that cool water is fighting a losing battle with a warming atmosphere, Karnauskas says. “This cooling trend will likely not last into the century. eventually it will be overwhelmed,” he says. But if some species are protected at least for a while, the Galapagos could become a gene bank that could be used to reseed damaged marine ecosystems elsewhere, Karnauskas suggests. “And it’s just beautiful that we’re talking about the iconic Galapagos.”
