This article was originally published by Hakai Magazine.
As a result of climate change, almost every part of the ocean is warming. But off the west coast of the Galapagos Islands 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 offshore water become a refuge for marine animals seeking a cold environment 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 at Boulder, the Galapagos cold pool is a product of the island’s topography—something that is unlikely to change due to rising 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 a deep ocean current colliding with islands in its wake.
By analyzing 22 years of ocean temperature data collected by the Argo floats, along with observations from satellites and cruises, scientists constructed temperature profiles around several equatorial islands and pinpointed the location of the Equatorial Hypertrophy—a cold, fast-flowing current that travels east about 100 meters below the surface of the Pacific Ocean. The EUC is held in place along the equator by the Coriolis effect, an inertial force caused by the Earth’s rotation. 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 makes the water in this cold pool generally more than 1 degree Celsius cooler than the water outside. The researchers found a similar but weaker effect west of the Gilbert Islands in the western Pacific Ocean.
In a separate study, Karnauskas found that in recent decades, the EUC has become increasingly powerful. It has also moved about 10 kilometers south, aligning its path more closely 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 who was not involved in the studies. “EUC’s cool water definitely has significant positive effects,” 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, including cold-shocked corals, causing bleaching and sometimes death.
In the near future, this cold shield will likely benefit life around the Galapagos and other equatorial islands. But it’s fighting a losing battle with a warm atmosphere, says Karnauskas: “This cooling trend probably won’t last the century. eventually it will be overwhelmed.”
However, if some species are protected for at least a little while, the Galapagos could become a gene bank that could be used to re-seed damaged marine ecosystems elsewhere, Karnauskas suggests: “And it’s just beautiful that we’re talking about the iconic Galapagos here.”