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By NASA
3 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Ice cover ebbs and flows through the seasons in the Arctic (left) and the Antarctic (right). Overall, ice cover has declined since scientists started tracking it half a century ago. Download this visualization from NASA’s Scientific Visualization Studio: https://svs.gsfc.nasa.gov/5099Trent Schindler/NASA’s Scientific Visualization Studio Winter sea ice cover in the Arctic was the lowest it’s ever been at its annual peak on March 22, 2025, according to NASA and the National Snow and Ice Data Center (NSIDC) at the University of Colorado, Boulder. At 5.53 million square miles (14.33 million square kilometers), the maximum extent fell below the prior low of 5.56 million square miles (14.41 million square kilometers) in 2017.
In the dark and cold of winter, sea ice forms and spreads across Arctic seas. But in recent years, less new ice has been forming, and less multi-year ice has accumulated. This winter continued a downward trend scientists have observed over the past several decades. This year’s peak ice cover was 510,000 square miles (1.32 million square kilometers) below the average levels between 1981 and 2010.
In 2025, summer ice in the Antarctic retreated to 764,000 square miles (1.98 million square kilometers) on March 1, tying for the second lowest minimum extent ever recorded. That’s 30% below the 1.10 million square miles (2.84 million square kilometers) that was typical in the Antarctic prior to 2010. Sea ice extent is defined as the total area of the ocean with at least 15% ice concentration.
The reduction in ice in both polar regions has led to another milestone — the total amount of sea ice on the planet reached an all-time low. Globally, ice coverage in mid-February of this year declined by more than a million square miles (2.5 million square kilometers) from the average before 2010. Altogether, Earth is missing an area of sea ice large enough to cover the entire continental United States east of the Mississippi.
“We’re going to come into this next summer season with less ice to begin with,” said Linette Boisvert, an ice scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It doesn’t bode well for the future.”
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Observations since 1978 show that ice cover has declined at both poles, leading to a downward trend in the total ice cover over the entire planet. In February 2025, global ice fell to the smallest area ever recorded. Download this visualization from NASA's Scientific Visualization Studio: https://svs.gsfc.nasa.gov/5521Mark Subbaro/NASA's Scientific Visualization Studio Scientists primarily rely on satellites in the Defense Meteorological Satellite Program, which measure Earth’s radiation in the microwave range. This natural radiation is different for open water and for sea ice — with ice cover standing out brightly in microwave-based satellite images. Microwave scanners can also penetrate through cloud cover, allowing for daily global observations. The DMSP data are augmented with historical sources, including data collected between 1978 and 1985 with the Nimbus-7 satellite that was jointly operated by NASA and the National Oceanic and Atmospheric Administration.
“It’s not yet clear whether the Southern Hemisphere has entered a new norm with perennially low ice or if the Antarctic is in a passing phase that will revert to prior levels in the years to come,” said Walt Meier, an ice scientist with NSIDC.
By James Riordon
NASA’s Earth Science News Team
Media contact: Elizabeth Vlock
NASA Headquarters
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Last Updated Mar 27, 2025 LocationNASA Goddard Space Flight Center Related Terms
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By NASA
6 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Located off the coast of Ecuador, Paramount seamount is among the kinds of ocean floor features that certain ocean-observing satellites like SWOT can detect by how their gravitational pull affects the sea surface.NOAA Okeanos Explorer Program More accurate maps based on data from the SWOT mission can improve underwater navigation and result in greater knowledge of how heat and life move around the world’s ocean.
There are better maps of the Moon’s surface than of the bottom of Earth’s ocean. Researchers have been working for decades to change that. As part of the ongoing effort, a NASA-supported team recently published one of the most detailed maps yet of the ocean floor, using data from the SWOT (Surface Water and Ocean Topography) satellite, a collaboration between NASA and the French space agency CNES (Centre National d’Études Spatiales).
Ships outfitted with sonar instruments can make direct, incredibly detailed measurements of the ocean floor. But to date, only about 25% of it has been surveyed in this way. To produce a global picture of the seafloor, researchers have relied on satellite data.
This animation shows seafloor features derived from SWOT data on regions off Mexico, South America, and the Antarctic Peninsula. Purple denotes regions that are lower relative to higher areas like seamounts, depicted in green. Eötvös is the unit of measure for the gravity-based data used to create these maps.
NASA’s Scientific Visualization Studio Why Seafloor Maps Matter
More accurate maps of the ocean floor are crucial for a range of seafaring activities, including navigation and laying underwater communications cables. “Seafloor mapping is key in both established and emerging economic opportunities, including rare-mineral seabed mining, optimizing shipping routes, hazard detection, and seabed warfare operations,” said Nadya Vinogradova Shiffer, head of physical oceanography programs at NASA Headquarters in Washington.
Accurate seafloor maps are also important for an improved understanding of deep-sea currents and tides, which affect life in the abyss, as well as geologic processes like plate tectonics. Underwater mountains called seamounts and other ocean floor features like their smaller cousins, abyssal hills, influence the movement of heat and nutrients in the deep sea and can attract life. The effects of these physical features can even be felt at the surface by the influence they exert on ecosystems that human communities depend on.
This map of seafloor features like abyssal hills in the Indian Ocean is based on sea surface height data from the SWOT satellite. Purple denotes regions that are lower relative to higher areas like abyssal hills, depicted in green. Eötvös is the unit of measure for the gravity-based data used to create these maps.NASA Earth Observatory This global map of seafloor features is based on ocean height data from the SWOT satellite. Purple denotes regions that are lower compared to higher features such as seamounts and abyssal hills, depicted in green. Eötvös is the unit of measure for the gravity-based data used to create these maps.NASA Earth Observatory This map of ocean floor features like seamounts southwest of Acapulco, Mexico, is based on sea surface height data from SWOT. Purple denotes regions that are lower relative to higher areas like seamounts, indicated with green. Eötvös is the unit of measure for the gravity-based data used to create these maps.NASA Earth Observatory Mapping the seafloor isn’t the SWOT mission’s primary purpose. Launched in December 2022, the satellite measures the height of water on nearly all of Earth’s surface, including the ocean, lakes, reservoirs, and rivers. Researchers can use these differences in height to create a kind of topographic map of the surface of fresh- and seawater. This data can then be used for tasks such as assessing changes in sea ice or tracking how floods progress down a river.
“The SWOT satellite was a huge jump in our ability to map the seafloor,” said David Sandwell, a geophysicist at Scripps Institution of Oceanography in La Jolla, California. He’s used satellite data to chart the bottom of the ocean since the 1990s and was one of the researchers responsible for the SWOT-based seafloor map, which was published in the journal Science in December 2024.
How It Works
The study authors relied the fact that because geologic features like seamounts and abyssal hills have more mass than their surroundings, they exert a slightly stronger gravitational pull that creates small, measurable bumps in the sea surface above them. These subtle gravity signatures help researchers predict the kind of seafloor feature that produced them.
Through repeated observations — SWOT covers about 90% of the globe every 21 days — the satellite is sensitive enough to pick up these minute differences, with centimeter-level accuracy, in sea surface height caused by the features below. Sandwell and his colleagues used a year’s worth of SWOT data to focus on seamounts, abyssal hills, and underwater continental margins, where continental crust meets oceanic crust.
Previous ocean-observing satellites have detected massive versions of these bottom features, such as seamounts over roughly 3,300 feet (1 kilometer) tall. The SWOT satellite can pick up seamounts less than half that height, potentially increasing the number of known seamounts from 44,000 to 100,000. These underwater mountains stick up into the water, influencing deep sea currents. This can concentrate nutrients along their slopes, attracting organisms and creating oases on what would otherwise be barren patches of seafloor.
Looking Into the Abyss
The improved view from SWOT also gives researchers more insight into the geologic history of the planet.
“Abyssal hills are the most abundant landform on Earth, covering about 70% of the ocean floor,” said Yao Yu, an oceanographer at Scripps Institution of Oceanography and lead author on the paper. “These hills are only a few kilometers wide, which makes them hard to observe from space. We were surprised that SWOT could see them so well.”
Abyssal hills form in parallel bands, like the ridges on a washboard, where tectonic plates spread apart. The orientation and extent of the bands can reveal how tectonic plates have moved over time. Abyssal hills also interact with tides and deep ocean currents in ways that researchers don’t fully understand yet.
The researchers have extracted nearly all the information on seafloor features they expected to find in the SWOT measurements. Now they’re focusing on refining their picture of the ocean floor by calculating the depth of the features they see. The work complements an effort by the international scientific community to map the entire seafloor using ship-based sonar by 2030. “We won’t get the full ship-based mapping done by then,” said Sandwell. “But SWOT will help us fill it in, getting us close to achieving the 2030 objective.”
More About SWOT
The SWOT satellite was jointly developed by NASA and CNES, with contributions from the Canadian Space Agency (CSA) and the UK Space Agency. NASA’s Jet Propulsion Laboratory, managed for the agency by Caltech in Pasadena, California, leads the U.S. component of the project. For the flight system payload, NASA provided the Ka-band radar interferometer (KaRIn) instrument, a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer, and NASA instrument operations. The Doppler Orbitography and Radioposition Integrated by Satellite system, the dual frequency Poseidon altimeter (developed by Thales Alenia Space), the KaRIn radio-frequency subsystem (together with Thales Alenia Space and with support from the UK Space Agency), the satellite platform, and ground operations were provided by CNES. The KaRIn high-power transmitter assembly was provided by CSA.
To learn more about SWOT, visit:
https://swot.jpl.nasa.gov
News Media Contacts
Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0307 / 626-379-6874
jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov
2025-040
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Last Updated Mar 19, 2025 Related Terms
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