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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
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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.

Deep-sea mining (DSM) not only poses significant environmental, social, and economic risks that may have far-reaching implications for coastal communities and Small Island Developing States (SIDS), it is also likely to negatively affect the business community, including insurers and investors, says a new study by researchers from the University of British Columbia and the Dona Bertarelli Philanthropy.

In an article published in Science Advances, a collaborative team led by the Woods Hole Oceanographic Institution (WHOI) presents a never-before-seen image of an oceanic transform fault from electromagnetic (EM) data collected at the Gofar fault in the eastern Pacific Ocean.

The locations of drainage divides determine how water flows across a landscape. Now, a new study has revealed how quickly these features can migrate when a region’s normally dry climate gets a little wetter.

Researchers used a combination of field observations, sediment dating, and numerical modeling to show how a river system in Israel’s Negev Desert has made sudden shifts in response to known wet periods. Drainage divides that migrated at an average rate of 1.1 kilometers (0.7 mile) per million years over the studied interval stalled and picked up speed in step with known shifts in the region’s climate.

“To my knowledge, this is the first study that directly measures rates of drainage divide migration,” said Mikaël Attal, a geomorphologist at the University of Edinburgh in Scotland who was not involved in the research. “This is important because drainage migration can have implications for understanding erosion across landscapes, our ability to infer tectonics from topography, and the management of water resources.”

Drainages Move Slowly, Then All at Once

Water falling on a landscape flows downhill, accumulates in rivers, and eventually drains into lakes, wetlands, or oceans. Drainage divides are topographic boundaries that control the water’s path.

“If a drop of water falls on one side or the other of a drainage divide, it will follow a different route,” Attal said. He used North America’s Great Divide as an example: “If a drop falls on the west side of the divide, it goes to the Pacific; if it falls on the other side, it goes to the Atlantic.”

A drainage divide migrates when the rivers on one side of the ridge erode more rapidly than on the other. In response, rivers may change their course or even reverse direction.

Because divide migration has a significant effect on landscapes, researchers are interested in how—and how quickly—it happens. But so far, it has been difficult to determine the rate at which drainage divides migrate on short timescales.

“Geomorphic markers capable of recording past divide locations, such as alluvial terraces, are often eroded away,” explained Elhanan Harel, a geomorphologist at the Geological Survey of Israel and a coauthor of the study, which appeared in Proceedings of the National Academy of Sciences of the United States of America.

Most of the movement happened in two intervals, during which the drainage divide migrated across the landscape at twice the average rate.

Previous studies have used cosmogenic nuclide dating to measure erosion on either side of drainage divides. These erosion rates, along with other variables, were fed into an equation that estimates the rate of drainage divide migration.

This approach, however, presents several drawbacks. The equation relies on a simplified geometric model of the drainage divide, which may not accurately describe a specific site. In addition, cosmogenic nuclide dating provides erosion rates that are averaged over a river basin, which may not match erosion at the drainage divide. The erosion rates inferred from cosmogenic nuclides are also time averaged, making it impossible to track short-term changes.

Harel and his coauthors overcame these difficulties by studying unusually well-preserved river terraces in Israel’s dry southern Negev Desert. River terraces, created as rivers slowly erode and leave behind steps that represent previous levels of the valley floor, are valuable markers of regional geomorphology. At the Negev Desert site, each terrace records a past location of the drainage divide, enabling Harel and others to trace the divide’s migration step by step.

The researchers used a technique called optically stimulated luminescence to date when the terraces formed. Collating dates on the sequence of terraces, they reconstructed the drainage divide’s 258-meter migration over the past 227,000 years.

Most of the movement, they found, happened during two intervals, from 245,000 to 183,000 years ago and 36,000 to 26,000 years ago, during which the divide moved across the landscape at twice the average rate.

Wet Climates May Drive Rapid Migration

Although the southern Negev Desert has been mostly dry for at least a million years, its arid state has been punctuated by occasional wet periods: One occurred around 220,000–190,000 years ago, and another took place between 35,000 and 20,000 years ago. These periods coincide with intervals of rapid drainage migration.

Increased weathering and the timing of groundwater recharge in the southern Negev indicate that extreme storms and floods occurred at those times.

The researchers simulated the physical processes of river incision to evaluate whether climate shifts could explain the observed divide migration rates. They found that a scenario assuming constant climate conditions couldn’t reproduce their observations from the Negev, but one that included intermittent climate shifts matched the results exactly.

“Our study provides the first direct evidence linking divide migration to climate fluctuations on much shorter timescales.”

The new analysis supports the idea that climate and rainfall drive landscape changes. “While previous studies have demonstrated that tectonic forces can drive divide migration over million-year timescales, our study provides the first direct evidence linking divide migration to climate fluctuations on much shorter timescales,” Harel said.

Attal agreed that the study helps researchers understand the connection between climate and drainage patterns. “It is very interesting that [the authors] found that the divide tends to migrate in bursts during wet periods,” he said.

This knowledge may be increasingly relevant as extreme weather events—such as severe rain, storms, and floods—become more common because of climate change. In flat areas with an abundance of loose sediment, severe flooding could divert rivers and shift drainage divides, causing permanent changes to the landscape.

“I think this work highlights that some landscapes may be highly sensitive to climate change,” said Attal.

—Caroline Hasler (@carbonbasedcary), Science Writer

Citation: Hasler, C. (2025), Climate shifts drive episodic drainage changes, Eos, 106, https://doi.org/10.1029/2025EO250139. Published on 14 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: Geophysical Research Letters

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.

Recent climate modeling studies have suggested that ocean heat content also changes on shorter timescales of just a few thousand years as a result of intermittent changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC)—a pattern of Atlantic Ocean currents that carries warm water north and cold water south. The models suggest that a weaker AMOC leads to increased ocean heat content. However, real-world evidence to support or refute AMOC’s potential influence on ocean heat content has been limited.

Grimmer et al. present the first record of ocean heat content during the ends of the last four ice ages and the subsequent warm periods, enabling the team to test modeling predictions against paleoclimate data.

To generate the new record, the researchers analyzed the ratios of specific noble gases trapped within 59 new samples from a 3,260-meter-long ice core drilled in East Antarctica as part of the European Project for Ice Coring in Antarctica (EPICA). The noble gas ratios in different ice layers serve as fingerprints of ocean heat content at various times in Earth’s past.

Analysis of the new record showed that at the end of each of the last four ice ages, ocean heat content generally increased alongside a weaker AMOC, as predicted by the models. These transitions to warmer interglacial periods, known as deglaciations, last several thousand years. The record also showed evidence of millennial-scale changes in ocean heat content that occurred alongside changes in ocean circulation. When the AMOC strengthened, ocean heat content either increased at a slower pace or decreased.

These findings align with the prior modeling predictions, supporting the idea that on millennial timescales, the AMOC plays a key role in controlling heat uptake by Earth’s oceans. In turn, this interaction likely influences subsequent sea levels, climate conditions, and atmospheric carbon dioxide levels. (Geophysical Research Letters, https://doi.org/10.1029/2024GL114415, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), When ice ages end, ocean circulation fine-tunes ocean heat, Eos, 106, https://doi.org/10.1029/2025EO250137. Published on 14 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.

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

Ice sheets are formed by the slow transformation of snow into ice. Large masses of ice, such as the Antarctic ice sheet, deform under their own weight and transport the ice from the interior of the continent to the coast, eventually breaking off and forming icebergs. The flow of ice is non-Newtonian, which means that its viscosity decreases as it deforms more. Recent research has shown that this effect may be even stronger than what current computer models use.

Getraer and Morlighem [2025] evaluate what the consequences of ice being an even more nonlinear material may be on its stability and contribution to sea level rise. The authors find that the sector of Thwaites glacier in West Antarctica would lose 32% more ice by 2100, and 70% by 2300. Current estimates of the future contribution of the ice sheets to sea level may therefore be strongly underestimated.

Citation: Getraer, B., & Morlighem, M. (2025). Increasing the Glen–Nye power-law exponent accelerates ice-loss projections for the Amundsen Sea Embayment, West Antarctica. Geophysical Research Letters, 52, e2024GL112516. https://doi.org/10.1029/2024GL112516

—Minghua Zhang, Former Editor-in-Chief, Geophysical Research Letters

Text © 2024. The authors. CC BY-NC-ND 3.0
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