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In estuaries—the transitional zones between rivers and the sea—fresh and salt water are constantly battling for dominance. But due to climate change, the saltwater is gaining ground. New research by Utrecht University's Institute for Marine and Atmospheric Research (IMAU) in collaboration with Deltares shows that saltwater intrusion—where seawater pushes inland into rivers—is on the rise globally.

Volcanoes inspire awe with spectacular eruptions and incandescent rivers of lava, but often their deadliest hazard is what quietly falls from the sky.

A team of scientists has cracked open one of meteorology's enduring mysteries—how hailstones grow inside storm clouds—using an innovative approach that analyzes chemical signatures locked in the ice. The findings, published in Advances in Atmospheric Sciences, challenge long-held assumptions about hail formation and could lead to improved severe weather prediction.

Indian Institute of Technology Gandhinagar-led research suggests climate change, increased monsoon rainfall and expanded groundwater pumping have driven substantial vegetation growth in the Thar Desert over the past two decades.

Each year in early March, when summer turns to fall in the Southern Hemisphere, New Zealand glaciologists gather at an airfield in Queenstown to embark on a predawn flight along the spine of the Southern Alps.

For hours, they twist in the Cessna’s narrow seats to train cameras on glaciers clinging to mountaintops. The images capture the glaciers’ vanishing contours and the shifting snowline—the demarcation between the remains of the winter snowpack and exposed glacial ice.

“It’s like a bank account,” said Andrew Lorrey, a climate scientist at the National Institute of Water and Atmospheric Research who has been coordinating the surveys for 16 years. “If we put in the same amount of snow in winter as we’re taking out in summer, the glacier would be in balance, melting at its terminus but advancing downhill due to gravity and replenishing the ice that’s lost.”

But the surveys, which have been running since 1977, show that summer melt now far exceeds winter snowfall and “we’re seeing the glaciers’ terminus and sides, the whole body, diminishing.”

New Zealand has lost more than a third of its glacial ice and the archipelago ranks third globally—after central Europe and the Caucasus—in the proportion of ice lost to rising temperatures, according to findings published in Nature by the first comprehensive global Glacier Mass Balance Intercomparison Exercise (GlaMBIE).

Global Assessment of Glacial Retreat

The project assessed observations from 35 international teams, with a goal of reconciling all methods used to track glacial mass changes. These methodologies range from in situ measurements (in which scientists stud individual glaciers with ablation stakes to record their shrinkage) to various satellite-borne sensors (which use optical, radar, laser, and gravimetry technologies to track changes in glacial surface elevation).

Bringing all these methodologies together, the GlaMBIE team produced a time series of global glacial mass change between 2000 and 2023, showing that collectively, the world’s glaciers lost 5% of their total volume. “This may not seem much,” said Michael Zemp, GlaMBIE project leader and director of the World Glacier Monitoring Service at the University of Zürich. But it means an annual global loss of 273 billion tonnes (301 billion tons) of ice.

“The ice lost each year amounts to the water intake of the entire global population in 30 years.”

“To put this in perspective,” Zemp said, “the ice lost each year amounts to the water intake of the entire global population in 30 years, assuming 3 liters per person a day.”

Andrew Shepherd, an Earth scientist at Northumbria University who was not involved in this project but has led a similar assessment of mass loss from polar ice sheets, welcomed the authoritative standardized framework provided by GlaMBIE.

Reconciling the different methodologies is important because “climate change isn’t smooth,” Shepherd said. Short-term in situ measurements can deliver contrasting results and each satellite technique has its strengths and weaknesses, but “bringing all methods together leads to a clearer picture of total ice loss,” he noted.

Although all areas experienced ice loss, the GlaMBIE results show significant differences between regions, ranging from 1.5% ice loss in the Antarctic to 39% in central Europe.

This map displays glacier mass changes from 2000 to 2023 as percentage loss (red slice in the pie chart) based on total glacier mass in 2000 (size of the pie chart). The colored stripes under each pie chart represent annual specific mass changes (in meter water equivalent) for a combined estimate (indicated with an asterisk) together with combined results from digital elevation model differencing and glaciological observations (Dg), altimetry (A), and gravimetry (G). Regional results are represented for hydrological years, that is, running from 1 October to 30 September in the Northern Hemisphere, 1 April to 31 March in the Southern Hemisphere, and over the calendar year in the low latitudes. Global results are aggregated for calendar years. Credit: The GlaMBIE Team. Community estimate of global glacier mass changes from 2000 to 2023. Credit: The GlaMBIE Team, 2025, https://doi.org/10.1038/s41586-024-08545-z

The largest overall contribution to ice loss (22%) comes from Alaska, said Caitlyn Florentine, a research physical scientist with the U.S. Geological Survey in Bozeman, Mont., and a GlaMBIE member.

Alaska, like the Canadian Arctic and Greenland, has enormous volumes of ice. But the relatively low elevation and latitude of Alaskan glaciers meant that these ice fields “were the biggest contributor to sea level rise [from glaciers] in the first 2 decades of this century and are projected to continue [to be] until 2100,” Florentine explained.

“Every centimeter of sea level rise exposes another 2 million people to annual flooding somewhere on our planet.”

The GlaMBIE results also revealed clear evidence of increasing melt rates, with a 36% jump during the second half of the study period, from 2012 to 2023. Mountain glaciers hold enough water to raise sea level by 32 centimeters if all were to melt. The ice that has already been lost from the world’s mountains has contributed 18% more to sea level rise than the loss from the Greenland Ice Sheet and more than twice the loss from the Antarctic Ice Sheet.

“Even small amounts of sea level rise matter, because it leads to more frequent coastal flooding,” Shepherd said. “Every centimeter of sea level rise exposes another 2 million people to annual flooding somewhere on our planet.”

Zemp hopes to focus future work on assessing how glacier melt affects seasonal runoff, and that requires ongoing access to satellite data and higher-resolution remote sensing techniques. As some satellites and sensors approach the end of their missions, he’s concerned about continuing the study. “If we are left without open access to high-resolution stereo imaging missions with a global coverage, we’d be blind to these changes,” he said.

Gone This Century

In addition to the ice sheets in Antarctica and Greenland, there are more than 275,000 glaciers—or crystal cones, as Zemp calls them—in mountain ranges from the tropics to the polar regions. Only about 500 are monitored up close.

One is Brewster Glacier in New Zealand, which Te Herenga Waka–Victoria University of Wellington glaciologist Lauren Vargo visits regularly. She drills ablation stakes into the ice in spring and retrieves their exposed parts in fall. In the 8 years between 2016 and 2024, she’s helped document that the glacier has shrunk by 24% and lost 17 meters in height.

New Zealand’s Brewster Glacier has shrunk by 24% in the 8 years between 2016 and 2024. Credit: Lauren Vargo

The retreat made Vargo’s latest visit, in March, physically taxing, she said. “The more melt that happens, the more stakes you have to collect,” she explained. “I don’t think I could have carried any more stakes.”

Many glaciers will not survive this century, Zemp said. Among these is one of his favorites, Oberaargletscher at Grimselpass in Switzerland, which Zemp has studied for almost a quarter of a century and, more recently, began visiting with his sons.

Oberaargletscher will be gone by 2050, regardless of any cuts to carbon emissions, Zemp said. While the retreat is “interesting to witness as a scientist,” he continued, “I am deeply sad that my sons and their generation will lose this fantastic glacier.”

—Veronika Meduna (@veronikameduna.bsky.social), Science Writer

Citation: Meduna, V. (2025), First global comparison of glacier mass change: They’re all melting, and fast, Eos, 106, https://doi.org/10.1029/2025EO250141. Published on 15 April 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: Journal of Geophysical Research: Biogeosciences

At the uppermost reaches of stream networks, headwaters dry up during the summer, then burst back into existence when spring brings rain. These nonperennial headwater streams are individually small, but collectively, they make up most of the length of global stream networks, and their chemistry is consequential for downstream waters.

As Earth warms, headwater streams are spending more time dried up and less time running. Zarek et al. investigated how increased dry time affects the nitrogen dynamics of streams throughout a watershed. To do so, they installed 21 sensors throughout a stream network in Alabama’s Talladega National Forest to collect information about stream drying and nitrogen content over the course of a year. They complemented these frequent measurements, taken every 15 minutes, with manual measurements taken during six campaigns across seven sites in the watershed.

The researchers expected that increased streamflow during springtime would wash nutrients downstream and raise nitrogen levels at the outlet of the stream network. Instead, they observed the opposite: When headwater streams increased streamflow, nitrogen concentrations at the outlet decreased. That could be because stream biota, such as riparian plants, in need of nutrients took up more nitrogen, keeping it from running downstream. Aquifer recharging in the spring, as a result of stream rewetting, may also spur chemical reactions that remove nitrogen and prevent its transport downstream.

The researchers also found that both nitrogen concentrations in the watershed and nitrogen removal rates were highest during the period when headwater streams were drying, findings they noted were “surprising.” They hypothesize that the high nitrogen concentrations could be because low streamflow creates ideal conditions for microbial activity that raises the nitrogen content of the water. The same conditions, they suggest, could also be ideal for allowing other microbes to remove nitrogen.

Position within the stream network was not a strong predictor of nitrogen concentrations, the researchers found. That observation suggests that many qualities of streams influence nitrogen dynamics and lead to heterogeneous nitrogen concentrations throughout the system. Their results highlight the need for additional spatially distributed stream monitoring, the researchers write. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2024JG008522, 2025)

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

Citation: Sidik, S. M. (2025), The “surprising” effect of drying headwaters on nitrogen dynamics, Eos, 106, https://doi.org/10.1029/2025EO250142. Published on 15 April 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.

Source: AGU Advances

The 2023 Kahramanmaraş earthquake struck southern Türkiye and Syria along the East Anatolian Fault. The magnitude 7.8 quake and its magnitude 7.5 aftershock devastated the region, killing tens of thousands of people and destroying hundreds of thousands of buildings.

Before the earthquake, seismologists warned that the area was ripe for a major seismic event. The region sits at the junction of the Anatolian, Arabian, and Eurasian plates and is rife with faults. In the years since the quake, scientists have been researching the seismic links between the main shock and aftershocks that struck across hundreds of kilometers.

Luo et al. used interferometric synthetic aperture radar on imagery collected by the Sentinel-1 satellite and Advanced Land Observing Satellite-2 (ALOS-2) to measure changes in land surface elevation following the earthquake.

The analysis identified eight areas outside the main rupture zone that saw localized changes in surface elevation triggered by the 2023 earthquake sequence, none of which were associated with known, discrete seismic events.

Of these events, four were typical aseismic events. Aseismic events involve geologic movement without earthquakes. For instance, in a slow-slip event, energy is released along a fault line gradually, over the course of weeks or months, causing land to move in a way that is imperceptible without scientific instruments.

Two others were seismic events—in which energy along a fault line was released abruptly—that were masked by the main earthquake’s seismic waves.

The remaining two events stood out. Dubbed “silent” events, the quakes—both greater than magnitude 5—did not produce local aftershocks or radiate detectable seismic waves as a typical earthquake would. The amount of stress along the fault did drop significantly after the tremor, however, similar to how it would in a regular earthquake. The authors suggest the aseismic events with a high drop in stress represent a previously unidentified transitional mode between regular earthquakes and slow-slip events.

Though more reviews of recent earthquakes are needed to determine whether these silent events were outliers, the findings could represent a missing slip type in models, with significant implications for scientists’ understanding of earthquake physics. The results also reveal new insights into seismic hazards in the vicinity of large, deadly quakes. (AGU Advances, https://doi.org/10.1029/2024AV001457, 2025)

—Aaron Sidder, Science Writer

Citation: Sidder, A. (2025), Türkiye-Syria temblors reveal missing piece in earthquake physics, Eos, 106, https://doi.org/10.1029/2025EO250144. Published on 15 April 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.

An analysis of satellite imagery of major river systems in the Philippines has revealed surprising insights into how rivers behave, with significant implications for river management in tropical settings.

New Curtin-led research has revealed that water played a far bigger role than previously thought in shaping Earth's first continents, transforming the planet's early crust and helping to build the landmasses we see today.

Mid-ocean ridge basalts (MORBs), located far from subduction zones, are typically thought to be unaffected by subduction processes. However, some MORBs display arc-like geochemical signatures—including negative Nb anomalies and elevated H2O/Ce and Ba/Th ratios—referred to as "ghost-arc signatures."

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

Water flowed on ancient Mars, but the timing, duration, effects, and exact nature of liquid water systems at or near the surface are still debated by planetary scientists. One setting where water could have been prevalent on early Mars is hydrothermal circulation—that is, the heat-driven circulation of warm water within the crust—under craters.

Mittelholz et al. [2025] test the presence and duration of hydrothermal systems under impact craters on early Mars by considering the effects that those systems would have on geophysical parameters of the Martian crust that we can observe today. In particular, the authors focus on the concepts that hydrothermal circulation would efficiently cool the local crust, hindering the deformation of craters that occurs when rocks are warm, and would alter the magnetization of the crust through chemical processes associated with the extensive water-rock interaction triggered by hydrothermal systems. The authors use sophisticated data analyses and numerical models to show that the orbital gravity and magnetic data collected by Mars-orbiting spacecraft are consistent with these effects of hydrothermal circulation in several regions on Mars.

The study finds that the water-rock interactions associated with hydrothermal circulation were not only present on early Mars, but long-lasting. Additionally, the study demonstrates how an interdisciplinary approach—tying together geophysics and geochemistry, gravity and magnetism, crust and core—can be used to address big picture questions about planetary habitability. The authors argue that a dedicated gravity mission in Martian orbit or regional magnetic studies conducted near the surface could further test these ideas.

Citation: Mittelholz, A., Moorkamp, M., Broquet, A., & Ojha, L. (2025). Gravity and magnetic field signatures in hydrothermally affected regions on Mars. Journal of Geophysical Research: Planets, 130, e2024JE008832. https://doi.org/10.1029/2024JE008832  

—Michael M. Sori, Associate Editor, JGR: Planets

Text © 2024. 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): Pontus Svensson, Patrick Hollebon, Daniel Plummer, Sam M. Vinko, and Gianluca Gregori

We extract electron transport properties from atomistic simulations of a two-component plasma by mapping the long-wavelength behavior to a two-fluid model. The mapping procedure is performed via Markov Chain Monte Carlo sampling over multiple spectra simultaneously. The free-electron dynamic structu…

[Phys. Rev. E 111, 045208] Published Tue Apr 15, 2025

The sun may rise every morning, but the amount of sunlight reaching Earth's surface can substantially vary over decades, according to a perspective article led by an international research team.

SummaryControlled-source marine seismic experiments are key in advancing our understanding of the Earth’s subsurface structure to study tectonic, magmatic, sedimentary and fluid flow processes. Joint acquisition of Wide-Angle Seismic (WAS) and Multi-Channel Seismic (MCS) streamer data stands as the most robust approach for marine exploration, however effectively mapping subsurface structure remains challenging. The lack of identifiable refractions as first arrivals at short offsets in WAS data creates shallow subsurface illumination gaps up to 6-8 km offsets around Ocean Bottom Seismometers or Hydrophones (OBS/OBH). This inadequate ray coverage, more pronounced in areas with deeper water column and lower seabed velocities, limits the performance of Travel Time Tomography (TTT) techniques. Velocity determination in the sedimentary layer and reflector location are affected, and errors propagate to deeper layers. This study integrates Downward Continuation (DC) to WAS data. Similarly to our former study where DC is applied to MCS data, redatuming WAS data involves solving the acoustic wave equation backward in time. This process virtually repositions the sources to the seafloor, revealing previously masked near-seafloor refractions as first arrivals. This transformation significantly enhances ray coverage in the shallow subsurface, leading to more accurate determinations of both seismic velocity and reflector geometry. By bridging theoretical concepts with a real data application, this study demonstrates the optimization of field seismic data for improved TTT results. This methodology is particularly beneficial for deep water exploration where spatially coincident WAS and MCS are jointly inverted. In such scenarios, DC-processed WAS data provides the refracted phases key for velocity determinations, and that are typically not present in MCS data due to insufficient streamer length relative to the water column depth. Additionally, we contribute to the community by releasing our open-source, High-Performance Computing (HPC) software for WAS data redatuming.

SummaryMexico City is one of the largest cities in North America, facing high seismic hazards and water supply problems. This paper presents an ambient seismic noise tomography of the city's south area in Xochimilco, where large amplifications have already been registered during subduction earthquakes. Eighty-four seismic stations have been installed, and their records processed. The tomography method combines the inversion of the Horizontal-to-Vertical Spectral Ratios (HVSR) and multimodal dispersion curves. The importance of considering a multimodal approach is justified in light of the complex geological setting. The dispersion curves analysis shows that the surface wave energy is divided over the fundamental and the higher modes, particularly between 50 and 300 m/s, and in the whole frequency range analyzed. We observe a spatially continuous decrease of the dominant peak frequency of the HVSRs toward the lake interior but a heterogeneous amplification. By analyzing the velocity profiles associated with the highest amplifications, we discovered that these latter result from the superposition of several resonance peaks. Their coincidence in frequency is due to the overall constant linear gradient velocity in the sedimentary basin crossed by several low-velocity anomalies due to high water content or high-velocity anomalies due to lavas. Although most of the shallow water is trapped in clay sediment, the velocity model also allows for identifying deeper water reserves. All these analyses are of fundamental importance for the correct seismic mitigation in Mexico City but might also be extended to other cities built on top of sedimentary basins.

Since December, Raphel Abraham has been struggling to cope with life in his flooded home on the banks of Vembanad Lake, in Edakochi, southern India.

The El Niño phenomenon in the South Atlantic and Benguela current, which flows along the west coast of southern Africa, have a significant impact on the tropical Atlantic region, leading to extensive effects on local marine ecosystems, African climates, and the El Niño Southern Oscillation. No one has been able to predict warm events in this region until now.

Much of Earth's heat uptake is passed to the ocean, making ocean heat content key for understanding long-term climate patterns. Ocean heat content is typically lower during ice ages and rises during warmer periods of glacier retreat. Over the past 1.2 million years, ice ages and interglacials have occurred in cycles lasting about 100,000 years, and we are currently in an interglacial period after the Last Glacial Maximum occurred about 20,000 years ago.

Scientists at the University of Miami's Alfred C. Glassell Jr. SUrge‐STructure‐Atmosphere INteraction (SUSTAIN) laboratory conducted a first-of-its-kind study into how waves form and increase in windy and hurricane conditions. The research, which reconstructs the two-dimensional profile of pressure and airflow above wavy surfaces, provides new insights into understanding ocean wave growth and its broader implications for weather forecasting and coastal resilience.

A little over 5 million years ago, water from the Atlantic Ocean found a way through the present-day Strait of Gibraltar. According to this theory, oceanic water rushed faster than a speeding car down a kilometer-high slope towards the empty Mediterranean Sea, excavating a skyscraper-deep trough on its way.