We've mapped the moon in more detail than our own ocean floor, but NASA's SWOT satellite takes us one step further. Using tiny changes in sea level to reveal underwater features, researchers have mapped vast, previously undiscovered areas of the ocean floor in unprecedented detail.

This global map of seafloor features is based on sea level data from the SWOT satellite. Purple areas represent lower-lying areas (such as seamounts and abyssal hills) compared to green areas. Eötvös is the unit of measurement used for the gravity data used to draw these maps. Image source: NASA Earth Observatory

These new maps reveal thousands of unknown underwater mountains and hills that shape deep-sea ecosystems and provide clues to Earth's geological history. With this breakthrough, scientists are quickly creating complete maps of the ocean floor decades ahead of what is possible with sonar mapping alone.

We have more detailed maps of the moon's surface than we have of Earth's ocean floor. For decades, scientists have been working to change this situation. Now, a team of NASA-backed researchers has made significant progress, using data from the SWOT (Surface Water and Ocean Topography) satellite to create one of the most detailed maps of the ocean floor to date.

Accurately mapping the ocean floor is critical for many reasons: from safe navigation and laying underwater communications cables, to understanding deep ocean currents, tides, and geological processes such as plate tectonics. Seafloor features, such as underwater mountains (seamounts) and smaller structures called bathyal hills, help control the flow of heat and nutrients in the deep ocean, creating the conditions for marine life to survive.

This map of seafloor features, such as seamounts southwest of Acapulco, Mexico, is based on sea surface height data from SWOT. Purple indicates lower areas relative to higher areas such as seamounts (shown in green).

Although sonar-equipped ships can capture highly detailed images of the ocean floor, only about 25% of the ocean has currently been mapped this way. To build a more complete picture of the ocean, researchers are increasingly turning to satellites.

Because geological features like seamounts and abyssal hills are more massive than their surroundings, they exert a slightly stronger gravitational pull, creating tiny, measurable bulges in the ocean surface above them. These subtle gravity signatures help researchers predict the types of seafloor features that form these bulges.

SWOT is a study conducted by the National Aeronautics and Space Administration (NASA) and the French National Center for Space Research (CNES), covering approximately 90% of the world every 21 days. Through repeated observations, the satellite is sensitive enough to capture these subtle differences in sea surface height caused by landform features with centimeter-level accuracy. Using a year's worth of SWOT data, geophysicist David Sandwell of Scripps Institution of Oceanography and his colleagues focused on seamounts, abyssal hills, and underwater continental margins where continental and oceanic crust meet.

Their mapping results are clearly visible on the global map (top) and in detailed views above and below. Areas of reduced gravity (purple) are associated with seafloor depressions, while areas of increased gravity (green) indicate the location of larger, higher landforms.

This map of Indian Ocean seafloor features, such as abyssal hills, is based on sea surface height data from the SWOT satellite. Purple indicates lower areas relative to higher areas (green) such as abyssal hills.

Previous ocean-observing satellites have detected giant versions of similar seafloor features, such as seamounts more than about 1 kilometer (3,300 feet) tall. SWOT satellites can detect seamounts at less than half that height, potentially increasing the number of known seamounts from 44,000 to 100,000. These underwater mountains extend into the water and influence deep ocean currents. This causes nutrients to accumulate along their slopes, attracting organisms and creating oases on the otherwise barren seafloor.

"The SWOT satellite has greatly improved our ability to map the seafloor," Sandwell said. Sandwell has been mapping the seafloor using satellite data since the 1990s and was one of the researchers responsible for creating a SWOT-based map of the seafloor published in the journal Science in December 2024.

SWOT's improved perspective also gives researchers a deeper understanding of Earth's geological history.

"Abyssal hills are the richest landforms on Earth, covering about 70 percent of the ocean floor," said Yao Yu, an oceanographer at Scripps Institution of Oceanography and lead author of the paper. "These hills are only a few kilometers wide and difficult to observe from space. We were surprised that SWOT was able to observe them so clearly."

Deep-sea hills form in parallel ribbons, like ridges on a washboard, that expand outward from the plate. The orientation and extent of these bands can reveal how the plates have moved over time. Deep-sea hills also interact with tides and deep-ocean currents, but researchers don't yet fully understand.

The researchers extracted information on nearly all of the seafloor features they expected to find in SWOT measurements. Now they are focusing on refining their picture of the seafloor by calculating the depth of observed features. This work complements the international scientific community's efforts to map the entire seafloor using shipborne sonar by 2030. "We won't be able to complete all of the shipboard mapping by then," Sandwell said. "But SWOT will help us fill this gap and bring us closer to achieving our 2030 goals."

NASA Earth Observatory map created by MichalaGarrison using SWOT data provided by Yu, Y. et al. (2024). Video produced by NASA Scientific Visualization Studio. The story was written by Jane Lee of the Jet Propulsion Laboratory and adapted from Earth Observatory.

Compiled from /scitechdaily