Gravity Anomalies Lead to Discovery of Vast Unknown Mountain Ranges Under the Ocean

Scientists have discovered almost 20,000 underwater mountains on the deep seafloor by examining images of the ocean surface captured from space and looking for gravitational perturbations, reports a new study. 

The research has nearly doubled the number of known “seamounts” from 24,643 to a total of 43,454, while also exposing fascinating details about the topography of the ocean floor and the vibrant ecosystems that thrive on submerged mountain slopes. 

Humans have been enchanted by mountains for thousands of years, leading to rich mythologies that have sprung up around beloved peaks like Olympus, Everest, and Kilimanjaro. But as land creatures, we are missing out on a whole other world of slopes and summits that exist under the sea, including the longest mountain range in the world, known as the mid-ocean ridge.  

Seamounts are active or extinct volcanoes that tower at least 3,300 feet above the ocean floor, which is about the same elevation as Mount Vesuvius in Italy. Many of these mountains have been discovered using sonar sensors onboard ships, but only a fifth of the ocean has been mapped with this technique.

Now, scientists led by Julie Gevorgian, a researcher at the Scripps Institution of Oceanography at the University of California, San Diego, have used satellite observations to discover thousands of seamounts that were previously unknown. 

With a space-down view, the researchers were able to pinpoint subtle perturbations on the ocean surface that are caused by the gravitational pull of hidden seamounts. The team used the technique “to update and refine a global seamount catalog, finding 19,325 new seamounts,” according to a recent study published in Earth and Space Science. 

“Geologically, better maps/catalogs of seamounts can provide insight into the composition and temperature of the mantle, track changes in isotopes, further understand the eruption process, and have a record of absolute plate motion,” said Gevorgian and her advisor David Sandwell, a professor of geophysics at Scripps and a co-author of the study, in an email to Motherboard.

“Ecologically, the catalog can help provide locations for biodiverse communities within the ocean,” they added. “Oceanographically, they can help in our understanding of ocean circulation.”

To that end, Gevorgian and her colleagues set out to probe the global oceans for signs of submerged seamounts with a new dataset of vertical gravity gradient (VGG) observations that measure the curvature of the ocean surface from space. A slew of recent satellite missions have dramatically improved the resolution and quality of VGG data, including the Indian-French mission SARAL/Altika, the American-French mission Jason-1, and the European missions CryoSat-2 and Envisat.   

“There are two advances,” Gevorgian and Sandwell explained. “First, Cryosat-2 and SARAL/Altika have collected altimeter data in non-repeat orbits since 2010 and 2016, respectively. This dramatically increased the spatial coverage over the oceans. Second, SARAL/Altika has a factor improvement in measurement accuracy with respect to all  other altimeters. This translates into improved VGG.”

These latest precision observations opened an entirely new window into the mountainous regions of the seafloor. The researchers meticulously identified the new seamounts by eye, and even recategorized some of the existing mountains recorded in the Kim–Wessel catalog, a global database for seamounts. 

“Based on the Kim and Wessel (2011) study and their projection, we had expected to find many seamounts,” Gevorgian and Sandwell said. “This was enabled by the lower noise of the new VGG. It is still exciting that we were able to expand the catalog by ~19,000 using this data.”

The results vastly expand our view of the ocean’s mysterious summits, and demonstrate the power of satellite observations as a means of exploring uncharted territory under the sea. Indeed, new missions such as NASA’s Surface Water and Ocean Topography (SWOT) spacecraft, could spot even more undiscovered seamounts. 

“The SWOT altimeter, launched by NASA in December 2022, could reduce the VGG noise by perhaps a factor of five,” Gevorgian and Sandwell concluded. “This will reveal many more smaller seamounts—perhaps another 20,000 or more.”

Update: This article was updated with comments from study authors Julie Gevorgian and David Sandwell.