Feed aggregator

SummaryThe Neuwied Basin within the East Eifel Volcanic Field (EEVF) is characterized by increased microseismicity, long hypothesized to be linked to the subsurface Ochtendung Fault Zone (OFZ). However, the source of this unrest remained elusive due to limited hypocenter resolution. Here, we present an extended local earthquake catalogue, compiled from a year-long Large-N deployment and a machine learning-based detection and location approach, including over 1,000 microearthquakes recorded between September 2022 and August 2023. This high-resolution dataset reveals new seismicity clusters, repeated waveforms, and distinct temporal bursts of activity, suggesting fluid-induced earthquake triggering. Probabilistic moment tensor inversion for 192 high-quality events (Mw 0.6-2.7) resolves predominantly strike-slip faulting along the OFZ, with localised clusters of normal faulting nearby, potentially associated with a previously unknown border fault of the NWB. Notably, we observe systematic rotations in P-axis orientations along the OFZ, which we interpret as localized stress perturbations induced by an overpressured reservoir beneath the Laacher See volcano - the youngest explosive eruption centre in the EEVF. These patterns, coupled with elevated magmatic CO2 emissions in the region and high waveform similarity, suggest that active magmatic and transcrustal fluid processes are influencing the stress regimes and driving the seismicity in the NWB. Our high-resolution seismicity and moment tensor catalogue offers new insights into the interplay between tectonics and fluid-driven processes beneath the youngest volcanoes in the EEVF.

SummaryThis study presents the first comparative measurements of seismic attenuation between Mauna Loa and Kīlauea volcanos on Hawai’i Island. The focus is on key physical variables found within Kīlauea, and extending our knowledge of these from Kīlauea to Mauna Loa. The measurements of attenuation, elastic/anelastic moduli (µ rigidity and K bulk), T temperature, P pressure, basalt activation energy, are uniformly applied to these adjacent volcanos (34 km separation) for comparative analyses. While numerous seismic attenuation studies have been conducted at Kīlauea, Mauna Loa has remained unexamined in this context until now. We extend previous methodologies to measure both shear (Qµ) and bulk (QK) attenuation over propagation paths from both volcanic calderas to the Aloha Cabled Observatory (ACO), located 442-464 km away at 4728 m depth. Utilizing earthquake displacement source spectra from shallow (near sea level) events beneath both calderas, we derive frequency-dependent effective Q values across the 2-35 Hz frequency band. Our analytical approach employs the t* formulation (ratio of travel time to Q) to separate attenuation along path segments, allowing direct comparison between the two volcanic systems. Results reveal that Mauna Loa exhibits substantially higher attenuation (lower Q values) than Kīlauea for both bulk and shear waves. At 10 Hz, Qµ is approximately four times higher for Kīlauea (∼400) than Mauna Loa (∼115), while QK displays even greater contrast with Kīlauea (∼425) exceeding Mauna Loa (∼25) by a factor of 17. Both volcanoes demonstrate QK < Qµ across most frequencies, emphasizing the significance of bulk losses in volcanic environments. This contradicts traditional assumptions held, that bulk attenuation is negligible in Earth. The pronounced difference in attenuation between these adjacent volcanoes, which share the same hot spot origin, cannot be explained solely by temperature-pressure dependent activation energy models. While we calculated expected Q variations using established basalt activation energies (59-68 kJ/mole), the observed differences exceed predictions by an order of magnitude. This suggests additional mechanisms are at work, likely involving partial melting processes. Our findings indicate that the internal structure of Mauna Loa may contain a greater proportion of partial melt or different melt geometry than Kīlauea, significantly affecting seismic wave propagation. At higher frequencies (17-33 Hz), both volcanoes show evidence of comparable scattering effects. This research provides new insights into the internal composition and dynamics of Hawaiian volcanoes, demonstrating that despite their proximity and shared magmatic source, Mauna Loa and Kīlauea possess distinctly different attenuation characteristics that reflect fundamental differences in their internal structure and melt distribution. These findings enhance our understanding of volcanic processes and contribute to improved interpretation of seismic data in volcanic environments.

ACM, the Association for Computing Machinery, today presented a 26-member team with the ACM Gordon Bell Prize for Climate Modeling in recognition of their project "Computing the Full Earth System at 1 km Resolution." The award honors innovative contributions to parallel computing toward solving the global climate crisis.

Publication date: Available online 17 November 2025

Source: Advances in Space Research

Author(s): Yu Chen, Guangxing Wang, Massimo Menenti

Publication date: Available online 17 November 2025

Source: Advances in Space Research

Author(s): Bushra Ansari, Sanat K. Biswas

Shackleford Banks is an 8-mile-long barrier island off the coast of North Carolina made up of sandy beaches, marshes, and maritime forests. There are no vacation rentals, boardwalks, or seafood restaurants serving the residents of Shackleford Banks. That’s because the residents are more than 100 wild horses that call the sandy dunes of this island home.

The delicate ecosystem of Shackleford Banks is facing the effects of a changing climate, such as increasingly volatile storms and flooding, drought, erosion, and saltwater intrusion. The island’s low elevation means its freshwater sources can be infiltrated with salt water during king tide events and storm surges. During stretches of drought, freshwater sources for the island’s equine residents can run dry, leaving the horses to compete for these vital resources.

“These horses have been out here long enough to adapt and survive, but freshwater availability is a critical resource,” said Matthew Sirianni, a geoscientist at East Carolina University who will present his research on 16 December at AGU’s Annual Meeting. Sirianni and colleagues monitored freshwater sources on Shackleford Banks, finding that horse behavior changed when freshwater sources were scarce. As saltwater intrusion and coastal hazards increase along the islands off the coast of North Carolina known as the Outer Banks, these findings can improve understanding of how to manage wildlife during a changing climate.

Foraging for Fresh Water

Wild horses have lived on Shackleford Banks for centuries. One theory suggests they arrived in the 1500s, swimming to shore after Spanish explorers were shipwrecked along the East Coast. Genetic testing suggests today’s Shackleford Banks horses are related to Spanish horse breeds, but early English settlers also brought horses with them that may also have escaped or been abandoned along the Outer Banks.

A horse digs in a pool of surface water at a groundwater seep during low tide on Shackleford Banks. These temporary pools will be flooded by the next high tide. Credit: Matthew Sirianni

Today, Shackleford Banks’s wild horse population must be kept to a manageable number so that the island and its resources aren’t overwhelmed. National Park Service workers dart the mares with hormonal birth control each year to keep herd size low. The small, hardy equines have adapted to a life of eating marsh grass, sea oats, and wax myrtle. They drink from ponds and freshwater seeps, and they also dig holes in the sand to reach the freshwater belowground when other sources have dried up.

In the new study, researchers monitored surface and groundwater levels and conductivity—a proxy measurement for salinity because higher conductivity values mean saltier water—in six water sources (two ponds, one groundwater seep, and three dig sites) located across the island.

“Barrier islands often develop a freshwater lens in the subsurface that floats on top of the denser, saltier water,” Sirianni said. “By monitoring water level and water conductivity, we can, over time, see whether the freshwater lens is shrinking, growing, or getting saltier, which tells us how the island’s water resources are responding to things like tides, storms, or droughts.”

Researchers installed motion-activated trail cameras near the water sources to capture still shots of animals drinking. They then grouped time-stamped photos to connect the horses’ drinking activities with water level and conductivity data. From there, they searched for water usage patterns, as well as for information about how long horse-dug holes (some as deep as 3 feet) stayed full of fresh water.

“Preliminary results from July 2024 to April 2025 indicate that horses spend more time drinking at dig sites, where conductivity is lower and more stable, compared to ponds and the groundwater seep, where conductivity is higher and more variable. However, when rainfall is low, dig sites often run dry, leading horses to drink from these higher-conductivity sources,” Sirianni said.

A Saltier Future?

“In the past, we’ve said that horses wouldn’t drink brackish water, but we were wrong. They do drink brackish water when that’s the only thing available to them.”

“With the research that [Sirianni] is doing, we have learned that these ponds can be really brackish,” said Linda Kuhn, a volunteer veterinarian with the National Park Service who was not involved with the research. “In the past, we’ve said that horses wouldn’t drink brackish water, but we were wrong. They do drink brackish water when that’s the only thing available to them.”

If the freshwater sources become saltier, history has already shown how the wild horses could be in trouble. On the island of Chincoteague, Virginia, equine deaths and illness were linked to a toxic increase in salinity in freshwater supplies, possibly wrought by the storm surge from Hurricane Erin.

It took 2 weeks for volunteers and observers to figure out what was wrong at Chincoteague. “Here we have [Sirianni] giving us data in real time. He also has cameras out there so he can see who’s drinking.” In light of what happened to the Chincoteague ponies after Hurricane Erin, “it’s just such an important study at this time,” Kuhn said.

“These horses have been here for many years and weathered many storms, so…they are a symbol of wildness and freedom even in the face of adversity.”

And with the potential for stronger, damaging storms in the future, the wild horses in this precarious island habitat may face more water and food shortages—along with danger from the land itself. Previous modeling studies suggest sea level rise will cause the already shallow groundwater table to reach the surface, as well as cause the shoreline to retreat as land subsidence and erosion worsen.

Sirianni plans to continue monitoring Shackleford Banks’s wild horses and water sources through at least July 2026 while he works on a final study manuscript about his findings. But he hopes to fund this research into the future. “These horses have been here for many years and weathered many storms, so I like that they are a symbol of wildness and freedom even in the face of adversity,” he said.

—Rebecca Owen (@beccapox.bsky.social), Science Writer

Citation: Owen, R. (2025), What salty water means for wild horses, Eos, 105, https://doi.org/10.1029/2025EO250433. Published on 21 November 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Source: Geophysical Research Letters

Ancient Mars boasted abundant water, but the cold and dry conditions of today make liquid water on the Red Planet seem far less probable. However, the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) detected strong radar reflections from a 20-kilometer-wide area over the base of Mars’s southern polar ice cap, hinting at the possibility of liquid water below the icy surface. Such a finding would have major implications for the planet’s possible habitability.

But sustaining liquid water underneath the ice might not be feasible without very salty brines or localized volcanic heat. Scientists have deliberated about other possible “dry” explanations for the bright reflections detected by MARSIS, such as layers of carbon dioxide and water ices or salty ice and clay causing elevated radar reflectivity.

Aboard the Mars Reconnaissance Orbiter, the Shallow Radar (SHARAD) uses higher frequencies than MARSIS. Until recently, though, SHARAD’s signals couldn’t reach deep enough into Mars to bounce off the base layer of the ice where the potential water lies—meaning its results couldn’t be compared with those from MARSIS.

However, the Mars Reconnaissance Orbiter team recently tested a new maneuver that rolls the spacecraft on its flight axis by 120°—whereas it previously could roll only up to 28°. The new maneuver, termed a “very large roll,” or VLR, can increase SHARAD’s signal strength and penetration depth, allowing researchers to examine the base of the ice in the enigmatic high-reflectivity zone.

Morgan et al. examined 91 SHARAD observations that crossed the high-reflectivity zone. Only when using the VLR maneuver was a SHARAD basal echo detected at the site. In contrast to the MARSIS detection, the SHARAD detection was very weak, meaning it is unlikely that liquid water is present in the high-reflectivity zone. The researchers suggest that the faint detection returned by SHARAD under this portion of the ice cap is likely due to a localized region of smooth ground beneath the ice. They add that further research is needed to reconcile the differences between the MARSIS and SHARAD findings. (Geophysical Research Letters, https://doi.org/10.1029/2025GL118537, 2025)

—Rebecca Owen (@beccapox.bsky.social), Science Writer

Citation: Owen, R. (2025), Maybe that’s not liquid water on Mars after all, Eos, 106, https://doi.org/10.1029/2025EO250437. Published on 21 November 2025. Text © 2025. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Journal of Geophysical Research: Solid Earth

Continental extension often unfolds in multiple deformation phases, where earlier faults steer the geometry and behavior of later ones. In a new study, Liu et al. [2025] explore the complexity of fault interaction by analogue modeling. 

The models reveal how shifts in stress—from biaxial to triaxial and back—govern the evolution of the fault network. In the triaxial phase, faults from the earlier biaxial phase are reactivated and new conjugate faults appear. When stress shifts back to biaxial, older faults may become inactive or partly reactivated. Stress conditions determine whether old faults block or guide the growth of new ones. Their modeling results are applied to explain the patterns of abandoned, reactivated and newly developed faults seen in the Aegean and Barents Seas. In general, their findings help to shed light on both the tectonic history of their study areas and the distribution of earthquakes.

Citaiton: Liu, J., Rosenau, M., Kosari, E., Brune, S., Zwaan, F., & Oncken, O. (2025). The evolution of fault networks during multiphase triaxial and biaxial strain: An analogue modeling approach. Journal of Geophysical Research: Solid Earth, 130, e2025JB031180. https://doi.org/10.1029/2025JB031180

—Birgit Müller, Associate Editor, JGR: Solid Earth

Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Author(s): H. Muneoka, T. Koike, S. Stauss, T. Ito, and K. Terashima

We conducted a comprehensive statistical analysis of the breakdown-voltage variations in helium near its critical point (5.2 K) using Weibull distribution analysis and Shannon entropy evaluation. Through detailed measurements at temperatures ranging from 5.1 to 5.5 K and densities from 5 to 115kg/m3…

[Phys. Rev. E 112, 055208] Published Fri Nov 21, 2025

body {background-color: #D2D1D5;} Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.

Rising sea levels have put thousands of facilities containing hazardous materials at risk of flooding this century, according to a new study published in Nature Communications. 

Global sea level rise is accelerating, leading to an increase in coastal flooding that scientists expect to worsen. As seas rise, floodwater reaches infrastructure that was not built to withstand it.

“Flooding from sea level rise is dangerous on its own—but when facilities with hazardous materials are in the path of those floodwaters, the danger multiplies.”

These extreme events can release toxins into the environment. For example, an estimated 10 million pounds of pollutants from refineries, petrochemical facilities, and manufacturing sites spilled into the environment following flooding from Hurricane Harvey in 2017.

The new study reports that 5,500 facilities containing hazardous substances are at risk of a similar event, threatening the health of nearby communities. 

“Flooding from sea level rise is dangerous on its own—but when facilities with hazardous materials are in the path of those floodwaters, the danger multiplies,” Lara Cushing, an environmental researcher at the University of California, Los Angeles and lead author of the new study, told The Guardian. 

In the study, scientists analyzed the location of 47,646 coastal power plants, sewage treatment facilities, fossil fuel infrastructure sites, industrial facilities, and former defense sites. Then, they used sea level rise projections under various climate scenarios to determine whether those sites were at risk from a 1-in-100-year flood event by 2100. 

They found that 11% of the sites analyzed were at risk of such a flood by 2100 in a high-emissions, business-as-usual scenario (RCP 8.5). Eighty percent of the at-risk sites were in just seven states: Louisiana, Florida, New Jersey, Texas, California, New York, and Massachusetts. Oil and gas wells made up a large proportion of sites considered to be at risk. 

These maps and graphs show the number and types of coastal facilities at risk of flooding due to sea level rise by 2050 and 2100 under a high-emissions, business-as-usual scenario. Credit: Cushing et al. 2025, doi:10.1038/s41467-025-65168-2, CC BY 4.0

In total, 22% of coastal sewage treatments facilities, 24% of coastal refineries, 44% of coastal fossil fuel ports and terminals, 12% of coastal industrial facilities, 21% of former coastal defense sites, and 21% of coastal fossil fuel and nuclear power plants are at risk of flooding by 2100. 

Disproportionate Effects

Marginalized groups are more likely to live near hazardous waste sites and industrial facilities, making these groups more vulnerable when such facilities flood. 

In the study, researchers analyzed the location of at-risk sites compared to community demographics. They found that households in Hispanic neighborhoods, households with incomes below twice the federal poverty line, and households that rented rather than owned their homes were especially likely to be located within one kilometer (0.62 miles) from a facility at risk of flooding.

 
Related

•  Read the study: “Sea level rise and flooding of hazardous sites in marginalized communities across the United States.”
•  Climate Central Report: Toxic Tides
•  Thousands of Toxic Sites Across U.S. Face Risk of Coastal Flooding
•  Sea Level Rise Threatens Hundreds of Wastewater Treatment Plants
• Sea Level Rise May Swamp Many Coastal U.S. Sewage Plants
 

“These projected dangers are falling disproportionately on poorer communities and communities that have faced discrimination and therefore often lack the resources to prepare for, retreat, or recover from exposure to toxic floodwaters,” Cushing said.

Reducing greenhouse gas emissions is key to slowing sea level rise and reducing flooding. The study’s projections showed that restricting greenhouse gas emissions to a low-emissions scenario (RCP 4.5) would reduce the number of at-risk sites from 5,500 to 5,138. 

In addition, the authors write that keeping communities safe from future hazardous floodwaters will require federal and state governments to “provide publicly available, accessible, and continually updated data on projections of [sea level rise]-related flooding threats.”

—Grace van Deelen (@gvd.bsky.social), Staff Writer

These updates are made possible through information from the scientific community. Do you have a story about science or scientists? Send us a tip at eos@agu.org. Text © 2025. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

The world is warming, yet summer temperatures on the southern slope of Mount Everest, measured continuously by the Pyramid Laboratory since 1994, have dropped over the past 15 years.

The reason? Cold downslope winds, caused by the increased temperature differences between the warmer air above the glacier and the air mass in direct contact with the glacier’s frozen surface.

These katabatic winds create a cooling effect around mountain glaciers, explained Thomas Shaw, a glaciologist at the Institute of Science and Technology Austria. “They’re melting more slowly than they would if there was a one-to-one correspondence between atmospheric temperature and the temperature of the glacier boundary layer.”

Scientists have made note of this phenomenon since the late 1990s, but studies have so far been limited to specific glaciers.

To understand the phenomenon’s extent and the factors influencing it on a global scale, Shaw and his colleagues collected and analyzed a dataset from 62 glaciers across 169 glacier campaigns, amounting to an unprecedented 3.7 million hours of air temperature data.

While much of the data were easily accessible, some were “almost the equivalent of being written on the back of a napkin,” said Shaw, who was able to include previously unpublished data from other researchers. “It takes a lot of emailing, clicking, finding, searching, and thinking, ‘Oh, I remember there was someone that published something on this.’”

Changing Projections

The study, published in Nature Climate Change, found that the glacier boundary layer warms an average of 0.83°C for every degree of ambient warming.

“This is not the only process affecting glacier melt, but it’s an important one that we didn’t have proof of before,” said Inés Dussaillant, a glaciologist at Centro de Investigación en Ecosistemas de la Patagonia in Chile who was not involved in the study.

“It may change our projections…and IPCC reports for the future evolution of glaciers or sea level contribution.”

Currently, this effect is not taken into account when modeling how glaciers will change over time, said Harry Zekollari, a glaciologist at Vrije Universiteit Brussel in Belgium who was not involved with the study. “It may change our projections and how we make them, and it may change projections and [Intergovernmental Panel on Climate Change] reports for the future evolution of glaciers or sea level contribution.”

According to Shaw’s analysis, the main factors driving the cooling effect are the temperature difference between the glacier boundary layer and the surrounding air, the size of the glacier, and humidity. Debris cover on the glacier and strong synoptic winds hinder the effect.

This phenomenon means that rising ambient temperatures actually increase the cooling effect on large glaciers—but only up to a point. “Glaciers are not protected because of this; they’re not cooling. It’s a bit of a misnomer,” said Shaw. While they are melting more slowly than would be expected with linear warming, the effect is still substantial. The study projects that globally, these near-surface cooling effects will peak during the late 2030s as temperatures rise.

As glaciers shrink in size, they will no longer be able to generate katabatic winds, and their rate of warming will begin to reflect ambient temperatures. According to the study, this will lead to accelerated melting from mid-century onward.

Going, Going, Gone

Shaw and his coauthors noted large regional variations in the data. While the cooling effect is not expected to peak until the 2090s for glaciers in New Zealand and the southern Andes, glaciers in central Europe have likely already passed this mark and are deteriorating at an increasing pace.

The study’s results tally with other findings. Earlier this year, a study of global glacier mass changes found that central Europe lost 39% of its ice mass between 2000 and 2023, faring the worst of all 19 regions studied.

A prime example is Pasterze, an Austrian glacier where research into the cooling phenomenon first started in the 1990s. “This was once a much larger glacier, with a much stronger observed katabatic cooling effect. Now it’s disintegrating very fast,” said Shaw, noting it will likely not be Austria’s largest glacier for much longer. “It’s already showing evidence of how rapidly glaciers can react to climate when they begin to disappear.”

But while troves of reliable long-term data are available for areas like the European Alps, Iceland, Svalbard, and western North America, glacier monitoring is not equally distributed worldwide. Dussaillant would like to see more support for regions where governments are not able to maintain ongoing glacier monitoring. “We cannot really say that this is the global picture, when in fact, some regions still have huge gaps which we need to fill and better understand.”

With around 200,000 glaciers worldwide, there is, indeed, still a lot of work to be done before a truly global picture emerges, said Zekollari. “But it’s a massive step forward compared to what we had.”

—Kaja Šeruga, Science Writer

Citation: Šeruga, K. (2025), Glaciers are warming more slowly than expected, but not for long, Eos, 106, https://doi.org/10.1029/2025EO250430. Published on 20 November 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Thin layers of sedimentary rock in Mars’s Gale Crater suggest that the planet once had a moon much larger than the two that orbit it today, according to work to be presented at AGU’s Annual Meeting 2025 on 17 December. Unlike the current Martian moons Phobos and Deimos, the gravitational pull of the hypothesized moon would have been strong enough to create tides in bodies of water on or below the planet’s surface.

The team analyzed images from cameras on the Curiosity rover, which has been trundling across Gale Crater since 2012. The Mars Hand Lens Imager, for instance, captures images with resolutions up to 13.9 micrometers per pixel.

Pictures of a rocky outcrop snapped during four Martian days in late 2017 and early 2018 revealed a section of fine, repeating layers in alternating light and dark colors. The researchers interpret those layers as tidal rhythmites, or sediments deposited by the regular back-and-forth sloshing of the tides.

“Our study provides sedimentary evidence for the case of tidally deposited rhythmites, hinting at a past larger moon for Mars.”

“Our study provides sedimentary evidence for the case of tidally deposited rhythmites, hinting at a past larger moon for Mars,” Ranjan Sarkar, a planetary scientist at the Max Planck Institute for Solar System Research in Gottingen, Germany, told Eos via email. “This, in turn, aligns with the hypothesis that Mars has repeatedly had larger moons that were tidally destroyed into rings, which then reformed into successively smaller moons.” That is, the larger moon or moons would have been pulled apart by the force of Martian gravity, which would have exerted a stronger pull on the planet-facing side of the moon than the opposite side.

The layering was detected at Vera Rubin Ridge on the flank of Mount Sharp, a sedimentary peak in the middle of Gale Crater. The studied area was about 35 centimeters long and 20 centimeters thick. Individual bands in the rock ranged from submillimeters to millimeters thick, with wider, light-toned bands and darker, thinner bands.

This graphic, for presentation at AGU’s Annual Meeting 2025, traces Curiosity’s path to the Jura outcrop on Vera Rubin Ridge. Color-enhanced images from the rover show the layered rocks interpreted as evidence of tidal rhythmites, with similar layers in an Earth setting shown for comparison. Click image for larger version. Credit: Ranjan Sarkar, Priyabrata Das, Suniti Karunatillake

Comparison with other observations along the ridge suggests the layers were deposited roughly 3.8 billion years ago, when Gale Crater contained a lake.

“Back-of-the-Envelope” Profile

Not all rhythmites are tidal: Similar sedimentary layers can be deposited by winds, seasonal variations in precipitation or glacier melts, or other processes, the researchers note.

“The finely laminated rhythmites in this crater are most likely varves, or deposits that reflect seasonal changes in the climate,” said Bob Craddock, a geologist at the National Air and Space Museum who was not involved in the study. More water flows into a lake during the warmer summer months, producing thicker sediment layers with larger grains compared to those laid during winter, he said. “As this continues through time, you get rhythmites.”

“It’s very tricky. We can’t be decisive, so our argument is one of consistency.”

Sarkar, however, said the structure of these layers doesn’t match what would be expected of seasonal deposits. “Annual varves usually show simple light-dark couplets, but we observe alternating thick-thin bands showing paired dark laminae,” he said. Such patterns “are commonly used as markers of tidal sedimentary signatures on Earth.”

“It’s very tricky,” said team member Suniti Karunatillake, a geologist and geophysicist at Louisiana State University. “We can’t be decisive, so our argument is one of consistency.…We felt that the observations are generally more consistent with a tidal setting.”

The layers probably were deposited with a “monthly” cycle of about 30 days, Karunatillake said. Even if Phobos or Deimos were much closer to Mars than they are today, neither is massive enough to create such a tidal cycle. Instead, combining this new work with modeling by previous researchers, the team estimated the tides were raised by a body at least 18 times the mass of Phobos, the larger moon, orbiting at an altitude of about 3 times the radius of Mars.

Phobos, photographed by the Mars Reconnaissance Orbiter, is not massive enough to have raised tides on Mars. It could be a remnant of a larger moon that was destroyed in a giant impact. Credit: NASA/JPL-Caltech/University of Arizona

“That’s our back-of-the-envelope calculation,” Karunatillake said. “Anything smaller and it would be difficult to induce this type of tidal activity, especially when you consider that Gale Crater is quite small as a water body on the planetary scale.”

The possibility of a smaller moon causing the observed tidal activity might be more realistic, Karunatillake added, if there were a connection between Gale Crater and the northern ocean, but no connection has yet been seen. However, even a subterranean link, such as the network of flooded caves and tunnels beneath Earth’s Yucatán Peninsula that leads to the Caribbean Sea, would suffice. “There are instances where you get tidal variations inland, as long as there’s a subsurface connection with the ocean,” he said.

Pondering the Martian Moons

Planetary scientists have pondered the origins of Phobos and Deimos extensively in recent decades. The original theory said they were captured asteroids, but it’s not easy for a planet to nab even one asteroid, much less two.

Some studies have suggested that Mars originally had a larger moon—either a captured asteroid or one that formed from an early giant impact. That body then could have been pulverized by the gravity of Mars or by its own collision, forming a ring that then gave birth to smaller moons. In fact, such a scenario could have played out multiple times. “Our study provides actual (ground) evidence, from measured laminae periodicities, for the predicted/hypothesized past larger moon,” Sarkar said.

The researchers are considering conducting a detailed celestial mechanics study to refine their estimates of the mass, distance, and orbital period of the proposed moon. They’re also examining two other sites in Gale Crater that appear to show similar tidal rhythms.

Any inconsistencies among the sites would “dispute our model, and possibly falsify it,” Karunatillake said. “But any agreement would take us toward a stronger argument for an ancient large moon.”

—Damond Benningfield, Science Writer

Citation: Benningfield, D. (2025), Sediments hint at large ancient Martian moon, Eos, 106, https://doi.org/10.1029/2025EO250434. Published on 20 November 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Geophysical Research Letters

How do the deep forces of the Earth’s interior shape surface faults, fractures and rivers? The results of a new global analysis show that rivers, faults, and stresses often align, but the degree of correspondence depends on fault type, stress source, and river size.

Kuhasubpasin et al. [2025] present a new framework to quantify the relative roles of lithospheric structures and mantle dynamics, offering fresh insights into how deep Earth processes govern the surface. A novel procedure is proposed to assess the relative role of mantle flow and lithospheric differences to the surface features, which may help constrain the individual forces acting to deform the lithosphere, creating topography. This holistic perspective on the coupled evolution of Earth’s interior and its surface shows how the interior of the Earth affects and perhaps even controls the surface.

Citation: Kuhasubpasin, B., Moon, S., & Lithgow-Bertelloni, C. (2025). Unraveling the connection between subsurface stress and geomorphic features. Geophysical Research Letters, 52, e2025GL116798. https://doi.org/10.1029/2025GL116798

—Fabio A. Capitanio, Editor, Geophysical Research Letters

Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Planet imagery shows the massive coal waste landslide at Mae Moh Mine. The failure was about 4.8 km long and 1.4 km wide

As I noted in an earlier post on this blog, at about 4 am on 4 November 2025, a very large landslide occurred in a coal waste pile at the Mae Moh Mine in Thailand. News reports have indicated that this failure, which occurred in a slope formed from coal waste material, caused significant damage.

Unfortunately, this area is very often cloudy, so obtaining good satellite imagery is a challenge. However, Planet captured an image on 15 November 2025 that shows a substantial part of the landslide.

The image below was captured on 28 October 2025, showing the site:-

The site of the 4 November 2025 landslide at Mae Moh Mine in Thailand. Image copyright Planet, captured on 28 October 2025, used with permission.

This image shows the aftermath of the landslide:-

The aftermath of the 4 November 2025 landslide at Mae Moh Mine in Thailand. Image copyright Planet, captured on 15 November 2025, used with permission.

And here is a slider to allow the images to be compared:-

Images copyright Planet

The crown of the landslide is to the west, with movement in an eastward direction. The landslide is very large – a rough estimate is 4.77 km long and 1.37 km wide. The archive of satellite image suggests that three was large-scale dumping of mine waste in the area that became the head scarp in the weeks ahead of the landslide. This freshly deposited material can be clearly seen in the pre-failure material, and is also discernible, after the failure. The presence of this material is a good starting point in terms of understanding the causes.

Cleaning up this site is going to be a very major, and very expensive, task.

Reference

Planet Team 2025. Planet Application Program Interface: In Space for Life on Earth. San Francisco, CA. https://www.planet.com/

Return to The Landslide Blog homepage Text © 2023. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: AGU Advances

The Hawaiian Islands formed through the Pacific plate’s movement over a relatively stationary, hot mantle plume, creating a succession of progressively older volcanic centers. New land continues forming on the Big Island’s south side, where the Kīlauea volcano system has remained active for decades. After nearly 40 years of spectacular surface flows entering the sea at Pu’u’ō’ō, volcanic activity shifted to the summit caldera.

Wu et al. [2025] employ seismological techniques to analyze subtle changes in shallow crustal velocities from 2013 to 2018, combining these data with geodetic and geological observations to better understand magma reservoir interactions between Kīlauea’s caldera and Pu’u’ō’ō. Their analysis reveals a fascinating sequence of cross-communication involving pressurization and magma transport processes affected by earthquake valving. When integrated with other monitoring and modeling, such research provides valuable insights into Kīlauea’s plumbing and basaltic volcanic systems more broadly. The work also reemphasizes the importance of seismological monitoring, and deployment of dense seismic networks at as many active volcanoes as possible would enable new comparative analyses.

Citation: Wu, S.-M., Lin, G., & Shearer, P. (2025). Seismic velocity monitoring reveals complex magma transport dynamics at Kīlauea Volcano prior to the 2018 eruption. AGU Advances, 6, e2025AV001759. https://doi.org/10.1029/2025AV001759

—Thorsten Becker, Editor, AGU Advances

Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Editors’ Vox is a blog from AGU’s Publications Department.

Land has been reclaimed for many centuries, and with the present-day demand for land, this process will continue in the future. The impact of such land reclamations has, up to now, been evaluated on a case-by-case basis, while studies integrating a wider range of land reclamation impacts is missing. Insights into the way tides interact with basin topography and the complex feedback mechanisms associated with fine-grained sediments is crucial to understanding the long-term response of coastal systems to a land reclamation.

A new article in Reviews of Geophysics synthesizes earlier findings on the effect of land reclamations on the coastal environment. Here, the lead author gives an overview of land reclamations, their impacts on coastal environments, and challenges for future research efforts.

Why and where is land reclaimed?

Fertile and low‐lying coastal landscapes are often densely populated because of their food supply (agriculture, aquaculture, and fisheries) and easy navigability (shipping lanes). At present 10% of the global population lives in Low Elevation Coastal Zones (LECZ’s; less than 10 meters above Mean Sea Level) and the population growth in LECZ’s is larger than the global average, especially in river deltas.

As this population pressure drives a continuous need for land, much of the low-lying land that was regularly inundated by the sea has been converted to agricultural land or urban environments. Especially the deltas of muddy rivers are suitable for reclamation, because of their shallow coastal waters and high sedimentation rates.

In our study we investigate how tide-influenced, typically muddy areas with wide intertidal areas, respond to reclamation by analyzing long-term datasets on tidal and bed level changes.

What kind of land reclamation techniques are used in such tide-influenced coastal environments?

Humans have reshaped deltas and other coastal areas for thousands of years. Traditional land reclamation techniques include the construction of wooden structures to dampen waves, allowing fine sediments to deposit. Eventually the area becomes vegetated and reclaimed through the construction of dikes. Although centuries old, this practice continues today, for example, in the Dutch-German Wadden Sea.

Figure 1: Traditional land reclamation technique in the Dutch-German Wadden Sea. Sediment is trapped by permeable brushwood groin fields (squares of 200 by 300 m) developing into saltmarshes. After construction of a dike the salt marshes are converted into agricultural land: the land protected by the sea dike in the picture above (lower right) was permanently reclaimed in 1969. Photo courtesy of Rijkswaterstaat Noord Nederland.

Other techniques include the construction of levees to convert wetlands into aquaculture or salt ponds (see Figure 1), or concrete revetments on the intertidal areas which gradually advance seaward. Such latter techniques are especially employed along the megadeltas of Asia. The most recent technique is the closure of tidal (sub)basins using barriers. Such closed basins may be converted into dry land (through pumping, creating polders) or remain reservoirs. In both cases, they profoundly influence the tidal dynamics of the coastal environment seaward of the closure for many decades or centuries.

How do these land reclamations influence coastal environments?

Land reclamations influence both the hydrodynamics (water levels and flow velocity) and the morphological response (erosion and sedimentation) of coastal environments. Both the hydrodynamic and morphological response are controlled by the reclamation type, the hydrodynamic conditions and sediment availability, and the location of the reclamation within the coastal environment.

Based on an analysis of all studies describing the effects of land reclamations, we have developed a classification scheme to explain the impact of reclamations on the coastal environment. A first major distinction herein is whether the reclamation takes place along an open coast, within a bay, or within an estuary. Open coast reclamations may lead to both erosion or sedimentation, likely depending on sediment availability. Reclamations in bays reduce tidal flows and mixing rates, and therefore lead to a reduction in water quality. The largest variability in response is observed in estuaries, where tides may amplify or dampen, and channels may erode or fill in (Figure 2).

Figure 2. Classification scheme conceptually describing how tides and bed levels respond to land reclamation. Credit: van Maren et al. [2025], Figure 9

Why do estuaries display such a large difference in response?

The large variability in estuarine response is caused by tide-topography interactions. Intertidal areas flanking an estuary reduce tidal energy and amplitude as the tide propagates through the estuary. Reclaiming land along the length of an estuary removes these intertidal areas and therefore leads to tidal amplification, especially if the estuary becomes more funnel-shaped (bottom left in Figure 2).

In contrast, reclaiming the most upstream intertidal areas of an estuary especially leads to a reduced tidal discharge (less water flowing in and out of the estuary with each tide) and therefore lower flow velocities (top right in Figure 2). As most estuaries are rich in sediments, such a reduction in flow velocities usually leads to sediment deposition. Reclaiming land at the mouth of an estuary only limitedly influences the tidal discharge, but the resulting smaller channel width leads to higher flow velocities and deepening of the channel (bottom right in Figure 2).

Why is the impact of land reclamation sometimes very large and prolonged?

Land reclamations may lead to an increase in tidal range of several meters but also to complete infilling of tidal channels. These adaptations are typically slow and may take decades to centuries. The impact is so large and takes such a long time because fine-grained sediments introduce a number of positive feedback mechanisms strengthening the effect of the original disturbance. We have identified five such feedback mechanisms. One example is the infilling of channels because upstream land reclamation reduces the tidal discharge (Figure 3).

Figure 3. Two positive feedback mechanism strengthening the initial response of tidal systems to land reclamation. Credit: van Maren et al. [2025], Figure 6 (modified)

As channel infilling continues, the tidal discharge further declines, promoting more sediment deposition. This infilling process slowly progresses in the seaward direction, in time leading to complete abandonment of a tidal system. Such impacts are most pronounced in branching tidal channel networks, such as the Ganges-Brahmaputra delta in Bangladesh. In such networks, infilling in one tidal channel may lead to large-scale erosion in another because of channel rearrangement, with its devastating effects illustrated in Figure 4.

Figure 4. Riverbank along a tidal channel in the Ganges-Brahmaputra delta eroding in response to land reclamation. Credit:  van Maren et al. [2023], Figure 13

Why are the effects of land reclamations relatively unknown?

The physical impact of land reclamations (changing tides, erosion, or deposition) are surprisingly poorly known. The ecological effects of land reclamations have been extensively studied, and these studies in turn synthesized in several reviews. The impact on tides and bed levels has received much less attention and has so far only been investigated in individual case studies, which do not reveal the full extent of land reclamation impacts. We believe that the number of studies are limited because (1) large amounts of land were reclaimed before data was collected; (2) the response time is slow and variable (and therefore changes are insufficiently correlated with a reclamation); and (3) many contemporary reclamations are executed simultaneously with other interventions (deepening of channels for navigation; reduction of sediment supply by upstream reservoirs) obscuring the effect of the reclamation.

What are key challenges for future research?

We have identified three key challenges for follow-up research. Firstly, the impact of reclamations is so large and prolonged because of a number of positive feedback mechanisms. A better understanding of such mechanisms is needed to explain historic changes but even more to predict future impacts of present-day land reclamations (especially tidal amplification which may influence high water level increase in the coming decades much more than sea level rise).

Secondly, we infer that land reclamation leads to higher suspended sediment concentrations in estuarine environments, negatively impacting coastal ecosystems but also being a key factor driving the positive feedback loops. However, studies relating suspended sediment dynamics to reclamations are limited.

And finally, more attention should be given to the long adaptation timescales. Present-day reclamations will impact their coastal environment for the coming decades to centuries. Forecasting how coastal systems will respond to rising sea levels, for example, is only possible with sufficient understanding of their slow response to existing reclamations.

—Bas van Maren (Bas.vanMaren@deltares.nl; 0000-0001-5820-3212), Delft University of Technology and Deltares, The Netherlands

Editor’s Note: It is the policy of AGU Publications to invite the authors of articles published in Reviews of Geophysics to write a summary for Eos Editors’ Vox.

Citation: van Maren, B. (2025), Echoes from the past: how land reclamation slowly modifies coastal environments, Eos, 106, https://doi.org/10.1029/2025EO255035. Published on 19 November 2025. This article does not represent the opinion of AGU, Eos, or any of its affiliates. It is solely the opinion of the author(s). Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Source: AGU Advances

Imagine the catastrophic winds of a category 5 hurricane. Now, imagine even faster winds of more than 100 meters per second, encircling the planet and whipping clouds across the sky, with no end in sight. This scenario would be astonishing on Earth, but it’s business as usual on Venus, where the atmosphere at cloud level rotates about 60 times faster than the planet itself—a phenomenon known as superrotation. In contrast, Earth’s cloud-level atmosphere rotates at about the same speed as the planet’s surface.

Prior research has explored the mechanisms driving atmospheric superrotation on Venus, but the details remain murky. New evidence from Lai et al. suggests that a once-daily atmospheric tidal cycle, fueled by heat from the Sun, contributes much more to the planet’s extreme winds than previously thought.

Rapid atmospheric rotation often occurs on rocky planets that, like Venus, are located relatively close to their stars and rotate very slowly. On Venus, one full rotation takes 243 Earth days. Meanwhile, the atmosphere races around the planet in a mere 4 Earth days.

To better understand this superrotation, the researchers analyzed data collected between 2006 and 2022 by the European Space Agency’s Venus Express satellite and the Japan Aerospace Exploration Agency’s Akatsuki satellite, which both studied Venus’s atmosphere by detecting how it bends radio waves. The research team also simulated superrotation using a numerical model of Venus’s atmosphere.

The analysis focused specifically on thermal tides—one of several atmospheric processes, alongside meridional circulation and planetary waves, whose interactions have previously been shown to sustain Venus’s superrotation by transporting momentum. Thermal tides are patterns of air movement that occur when sunlight heats air on the dayside of a planet. Venusian thermal tides can be broken into two major components: diurnal tides, which follow a cyclical pattern repeating once per Venusian day, and semidiurnal tides, which have two cycles per day.

Earlier research suggested that semidiurnal tides are the main thermal tide component involved in superrotation. However, this study—which includes the first analysis of thermal tides in Venus’s southern hemisphere—found that diurnal tides play a primary role in transporting momentum toward the tops of Venus’s thick clouds, suggesting diurnal tides are major contributors to the rapid winds.

Though the researchers note that further clarification of the contributions of diurnal tides is needed, the work sheds new light on Venus’s extreme winds and could aid meteorological research on other slowly rotating planets. (AGU Advances, https://doi.org/10.1029/2025AV001880, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), Key driver of extreme winds on Venus identified, Eos, 106, https://doi.org/10.1029/2025EO250436. Published on 19 November 2025. Text © 2025. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

A new tool aims to do for heat waves what Saffir and Simpson did for hurricanes.

CalHeatScore, an online mapping tool developed by the California Office of Environmental Health Hazard Assessment, ranks heat wave risk on a straightforward scale of 0 to 4. And just like the Saffir-Simpson scale for hurricane strength, CalHeatScore delivers its warnings days in advance. It’s designed to help Californians prepare for heat emergencies and uses socioeconomic factors to tailor information for each individual zip code.

“[CalHeatScore] gives you a warning for your community that reflects the characteristics of your community.”

“It gives you a warning for your community that reflects the characteristics of your community,” explained John Molitor, an environmental data scientist at Oregon State University who helped build the tool.

The hyperlocal method provides meteorologists, emergency managers, and the public with a shared understanding of risk during California’s extreme heat. Molitor and his colleagues will share their work at AGU’s Annual Meeting 2025 in New Orleans on 16 December.

Scorching in Sacramento

CalHeatScore was born during a heat wave. Legislators had been pushing for a warning system for months, and the bill was finally approved in September 2022 during a 10-day heat wave that broke 1,500 temperature records across California. The heat wave caused 395 excess deaths in the state, 4 times the toll of California’s deadliest wildfire, according to the Los Angeles Times.

The tool—officially dubbed the California Communities Extreme Heat Scoring System and launched in December 2024—was designed to prevent future heat deaths by providing a streamlined and site-specific warning system. It includes targeted public health information, like community heat risk and the locations of the nearest public cooling centers.

Building a Model

CalHeatScore draws from a range of data sources, recognizing that heat risk is more than just temperature.

First, developers established a baseline using temperature data and emergency room visits from 2008 to 2018, looking specifically for diagnoses that increase with heat. The current operational model uses zip codes as a proxy for socioeconomic data, while a second-stage model will add specific population data to pinpoint communities of concern.

Other warning systems look at empirical distributions of heat, Molitor explained, but CalHeatScore looks for causal effects. The interdisciplinary team of physicians, health experts, and data scientists is specifically looking for drivers of heat impacts.

“People experience heat very differently through space and time,” Molitor said. A community with swimming pools and air-conditioning will experience a 100°F day different than a neighborhood of pavement and parking lots. Similarly, indoor office workers are protected from the heat in a way roofers, gardeners, and carpenters aren’t. By considering factors like age brackets and average income, CalHeatScore can determine the heat-related health risk for a community.

The platform’s clickable, searchable map is built on spatial modeling. “What happens in one zip code is going to be highly informed by what happens in nearby zip codes,” Molitor said. Multilevel modeling “is allowing us to take the data and drill down into all these little zip codes and come up with an appropriate heat warning system for each,” he said.

Decisionmaking Data

All that complexity results in a very simple scale. Heat risk is ranked 0 (low) through 4 (severe) and provided for the next 7 days.

That’s a useful approach, said Ashish Sharma, an atmospheric scientist at the University of Illinois Urbana-Champaign who was not involved in the project.

“If we look at decisionmaking, it’s binary. Either you act upon it, or you don’t,” he said. “Combining this information at the zip code level can really improve decisionmaking.”

But while the tool has a lot of strengths, the current map seems geared more for agencies and governments than the public, he noted. He hopes future iterations are more user-friendly.

To that end, the CalHeatScore team is exploring options to develop a mobile app. That would be a helpful addition, said Amy Cilimburg, the director of Climate Smart Missoula who’s also worked on local heat mapping. A phone app could allow a football coach on the sidelines or a daycare director on the playground to plan their week around the heat.

“There is a lot of utility and strength in a hyper-local map,” she said. The next test is making sure people know about the tool and start making decisions based on it.

Expanding the Map

The developers aim to expand awareness at the AGU Annual Meeting, sharing their work with an international audience. CalHeatScore is replicable. Any state or country with similar data could develop a 7-day warning system.

“What we have here is really advanced, and we’d like to be doing this for other jurisdictions.”

“What we have here is really advanced, and we’d like to be doing this for other jurisdictions,” said David Eisenman, a project principal investigator, professor of medicine, and codirector of the Center for Healthy Climate Solutions at the University of California, Los Angeles.

The blend of health outcomes, temperature levels, and demographic data is “a really unique approach,” Eisenman said.

CalHeatScore is built with health outcomes and heat vulnerability in mind. When the next heat wave rolls through California, residents will have a new way to communicate and tolerate the temperature.

—J. Besl (@j_besl, @jbesl.bsky.social), Science Writer

20 November 2025: This article has been updated to correct the role of David Eisenman.

Citation: Besl, J. (2025), New tool maps the overlap of heat and health in California, Eos, 106, https://doi.org/10.1029/2025EO250432. Published on 19 November 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Source: Earth’s Future

Water levels are creeping upward on shorelines across the world, and decisionmaking systems are not keeping up. One barrier to including sea level rise projections in adaptation plans is limited information on the full range of possible outcomes.

Substantial scientific uncertainty exists around how quickly ice sheets could collapse. This uncertainty means high-end sea level rise projections have been particularly tough for coastal planners to incorporate into their risk assessments for critical infrastructure such as nuclear power plants. In the United Kingdom, current official guidance states that planners should consider a worst-case scenario of 1.9 meters of sea level rise by 2100, but recent scientific evidence suggests that worse scenarios are plausible. Given the broad range and large uncertainty surrounding high-end projections, new tools for decisionmakers are sorely needed.

Weeks et al. present a new decisionmaking framework that includes a “decision-game” approach. This decision-game approach involves a time-step based progression through a plausible sea level rise scenario, allowing participants to prime long-term thinking skills, analyze impacts of previous decisions, and test their strategies for adaptation. The new framework, coproduced by the United Kingdom’s Met Office and Environment Agency, also incorporates scientific advances that have taken place since the last major update to high-end sea level rise projections in 2009.

To test their framework, the researchers held a decision-gaming workshop that was attended by consultants, coastal risk management experts, and climate change advisers. The researchers presented a hypothetical U.K. coastal city to the participants and gradually revealed the local sea level change over the 21st century and beyond for a high-end scenario. Participants held nuanced discussions and gained a deep understanding of the ramifications that their adaptation planning decisions would have over time, the researchers report. With widespread deployment, the framework could help coastal communities build resilience against rising waters. The researchers also note that the approach could be adapted to help make decisions about managing other climate hazards in various regions. (Earth’s Future, https://doi.org/10.1029/2025EF006086, 2025)

—Saima May Sidik (@saimamay.bsky.social), Science Writer

Citation: Sidik, S. M. (2025), A new way for coastal planners to explore the costs of rising seas, Eos, 106, https://doi.org/10.1029/2025EO250375. Published on 18 November 2025. Text © 2025. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

About 1.5 million years ago, the mid-depth waters of the tropical Pacific Ocean suddenly grew cooler. The change came rapidly, and it spread across thousands of kilometers.

Before then, Earth’s climate had been relatively stable. Cycles of ice ages and interglacial periods had already begun, but they were shorter, and the tropical Pacific remained warm. Its surface temperature barely changed even as polar ice advanced and retreated.

So how did the waters suddenly become cold?

“We’re usually interested in the mid-depth waters—not the surface, not the deep ocean—because that’s where the music is.”

A new study published in Communications Earth and Environment suggests that the cold water came from the Southern Ocean and traveled northward through ocean tunnels into the tropics. An ocean tunnel, the research explains, describes a “channel for water masses that connects different oceanic and consequently, atmospheric regions.”

“We’re usually interested in the mid-depth waters—not the surface, not the deep ocean—because that’s where the music is,” said Jacek Raddatz, a climate scientist at GEOMAR Helmholtz Centre for Ocean Research Kiel, in Germany, and first author of the study.

“The Pacific is the largest ocean and important for global circulation and climate,” he continued. “That’s why we focused our study on the tropical Pacific.”

Tunnels of Colder, Fresher Water

The researchers analyzed tests of planktonic foraminifera (forams) recovered from a sediment core drilled from the Manihiki Plateau, a submerged ridge in the tropical South Pacific. The plateau is located at the eastern edge of the Western Pacific Warm Pool, the region with the highest ocean temperatures in the world.

The team measured magnesium-to-calcium ratios and oxygen isotope values in tests of two species of forams. One species lived near the surface, and the other lived about 400 meters down. With those values, the scientists reconstructed past temperatures and salinity spanning a period from about 2.5 million to 1 million years ago.

“At the Manihiki Plateau, we see that around 1.5 million years ago, there’s a drop in both temperature and salinity,” said Raddatz.

This timing matched a major growth of Antarctic ice.

The new research indicates cold Antarctic water traveled northward through the Pacific’s mid-depths as a pulse, a process known as ocean tunneling.

“Cold water forms off places like Chile, Peru, and California and slowly sinks. It moves toward the equator beneath the surface,” explained Matt Luongo, a climate scientist and postdoctoral researcher at the University of Washington, in Seattle. He was not involved in the study. “If that water becomes cooler or fresher, then maybe…10 to 20 years later, the equator ends up bringing up cooler water too. That’s basically how ocean tunneling connects distant parts of the ocean.”

Raddatz and his fellow researchers also examined how the cooling was related to Earth’s orbital cycles: eccentricity, or the shape of Earth’s orbit; obliquity, or the angle at which Earth’s axis is tilted with respect to its orbital plane; and precession, or the direction Earth’s axis is pointed.

They found a consistent pattern. “We see the same increase in obliquity-related signals in Antarctic ice volume, in midlatitude temperature reconstructions, and in our salinity record,” Raddatz said. “That led us to conclude that they’re all connected through the same mechanism.”

Raddatz and his colleagues think the cooling may have been an early step toward the period when Earth’s ice ages grew longer and more intense. “We think this might be a first step that led, maybe, to the Mid-Pleistocene Transition.”

Interesting, but Not Definitive

Luongo agreed the study shows that South Pacific waters did chill out and freshen up about 1.5 million years ago and that the source of these changes came from the Southern Hemisphere. The research is “interesting, because it helps explain why the thermocline in the equatorial Pacific is so cold and fresh,” he said.

But he also cautioned against directly linking the changes to Antarctic ice growth. “It’s suggestive of the ice sheet, the wiggles match, but it also could be something else,” said Luongo. “There are a lot of things that can cause freshening of the waters.”

Raddatz and his colleagues plan to extend their work to other ocean basins. They want to add nutrient and carbon measurements to build a fuller picture of how mid-depth waters evolve. “If we understand these variations,” he said, “we can also explain the growth and decline of biodiversity hot spots in the deep sea.”

—Larissa G. Capella (@CapellaLarissa), Science Writer

Citation: Capella, L. G. (2025), Ocean tunneling may have set off an ancient Pacific cooldown, Eos, 106, https://doi.org/10.1029/2025EO250428. Published on 18 November 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.