A map of the new seamount reveals 19,000 submarine volcanoes

The 4,776-meter-tall Bubble Seamount in the South Pacific (right) has been mapped by sonar. Image source: Office of Oceanographic Exploration and Research, National Oceanic and Atmospheric Administration

The new seamount catalogue was recently published in Earth and Space Science, which according to Larry Mayer, director of the Center for Coastal and Ocean Mapping at the University of New Hampshire, is “a big step forward.”

In addition to posing a threat to navigation, seamounts contain rare earth minerals, making them commercial targets for deep-sea miners. They are important oases for marine life, and their size and distribution also provide clues to plate tectonics and magmatic activity.

“The better we know about the shape of the seafloor, the better we can prepare for climate change.” John Lowell, chief hydrosurveyor at the National Geospatial-Intelligence Agency (NGA), said seamounts are “agitators” that help control large-scale ocean flows that sequester large amounts of heat and carbon dioxide. The NGA is responsible for satellite mapping for the U.S. military.

In 2005, the USS San Francisco nuclear submarine crashed into an undersea volcano at ultra-high speeds, killing one crew member and injuring many others. In 2021, this happened again when the USS Connecticut nuclear submarine crashed into a seamount in the South China Sea, damaging its sonar array.

Since sonar has mapped only 1/4 of the seafloor, it is unknown how many seamounts still exist. But radar satellites that measure the height of the ocean can find them. More than 19,000 new seamounts have been added to high-resolution radar data, but most of the ocean remains undetected by sonar. “It’s unbelievable.” David Sandwell, a marine geophysicist at Scripps Oceanographic Institution, said.

After the San Francisco accident, Sandwell and his colleagues received funding from the Navy and NGA to search for seamounts via satellite. They have found thousands, 700 of which pose a threat to submarines. But the team knew that their first seamount catalog wasn’t complete enough. Now, with data from high-resolution radar satellites, including the European Space Agency’s CryoSat-2 and the Indian and French space agencies’ SARAL, Sandwell said, the team can detect seamounts up to 1100 meters high, which is close to the lower limit of seamounts.

Seamounts usually appear in a chain. Carmen Gaina, a geophysicist at Queensland University of Technology, said the seamount catalogue would bring direct benefits to research on Earth’s interior. New seamounts discovered in the northeastern Atlantic could help trace the evolution of mantle plumes that fuel Iceland’s volcanoes. The survey also found seamounts near a ridge in the Indian Ocean, where new crust formed as tectonic plates separated. Gaina says this suggests that there is an alarming amount of volcanic activity in an area once thought to be magma-starved.

To biologists, the steep slopes of seamounts resemble crowded skyscrapers with corals and other marine life. “They are oases of biodiversity and biomass.” Amy Baco-Taylor, a deep-sea biologist at Florida State University, said. But biologists still debate the role seamounts play in marine biodiversity.

“If we don’t know where they are, we can’t protect them.” Chris Yesson, a marine biologist at the Zoological Society of the Zoological Institute of London, said. A map of seamounts will allow them not to waste much time. Previously, Yesson and colleagues had traveled to the Indian Ocean to study a seamount and found that it was a phantom caused by errors in sonar depth records.

The new map could not be more important in understanding the conveyor belts of ocean currents that surround the globe. Ocean currents transport heat from the equator to the poles, where the water cools and increases density until it subducts downward, carrying heat and carbon dioxide into the abyss. But the flip side of this perpetual motion machine — deep-sea waters that defy gravity and rise upwards — has long been a mystery.

“Upwelling” was once thought to be driven by turbulence at the boundary between deep ocean layers of different densities, occurring uniformly throughout the ocean. Now, researchers think it focuses on seamounts and ridges. Brian Arbic, a physical oceanographer at the University of Michigan, Ann Arbor, said: “With terrain, a lot of interesting things happen. ”

Jonathan Gula, a physical oceanographer at the University of West Brittany, says that when currents hover around seamounts, they create turbulent “wake vortices” that provide energy to push cold water upwards. In an unpublished study, Gula and co-authors found that these wake swirls make seamounts a major contributor to the upward mixing of the oceans and a central player in climate. Gula added that because the team relied on the old seamount catalogue rather than the new one, the seamount impact could be greater.

The seamount catalog is sure to expand further with the launch of the Subsea 2030 project, an international project to accelerate high-resolution sonar mapping led by Mayer. NASA’s Surface Water and Ocean Topography satellite, launched in December 2022, can measure water surface height within a few centimeters. Mayer said that given the cost of sonar-mapping voyages, better remote sensing technology would be welcome. (Source: Li Huiyu, China Science News)

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