Source: AGU Advances

This is an authorized translation of an Eos article. Esta es una traducción al español autorizada de un artículo de Eos.

No se tienen registros suficientes en las bases de datos globales de los peligros meteorológicos extremos. Por ejemplo, los eventos donde las temperaturas son potencialmente mortales y que se ajustan a las normas climatológicas generalmente no son incluidos en los estudios de riesgos, y las inundaciones locales o regionales a menudo suelen pasar desapercibidas para los instrumentos satelitales.

En los últimos 20 años Texas ha experimentado una cantidad inusualmente alta de fenómenos climáticos extremos, incluyendo un incremento en inundaciones y olas de calor. Usando datos satelitales de fácil acceso de precipitación y temperatura tomados diariamente, Preisser y Passalacqua crearon una visión más amplia de los riesgos por inundaciones y olas de calor que han afectado al estado en los últimos años.

Al consultar los datos de precipitación del 2001 al 2020, los investigadores definieron como un evento de inundación peligrosa a aquellos que ocurren en promedio una vez cada dos años o más, lo que significa que un evento de esa magnitud ocurre en un área determinada con una frecuencia que no supera los dos años. Compararon sus resultados con los registrados en la Base de Datos de Eventos de Tormentas de la NOAA y la base de datos del Observatorio de Inundaciones de Dartmouth (DFO por sus siglas en inglés). Su análisis detectó tres veces más inundaciones que en la base de datos del DFO y se identificaron daños adicionales de $320 millones de dólares.

El equipo también amplió el análisis sobre el calor extremo. En muchos estudios previos sobre amenazas múltiples sólo se consideraron las olas de calor, donde las temperaturas superaron un percentil, como el 90 o el 95, durante tres días seguidos. Este estudio también consideró los periodos donde la temperatura de globo de bulbo húmedo (índice WBGT) supera un umbral de salud de 30°C, en lugar de un percentil determinado. Bajo esta definición, los científicos determinaron que, entre 2003 y 2020, Texas vivió 2,517 días con eventos peligrosos de calor, lo que equivale a casi el 40% de los días dentro de este periodo. Estos eventos afectaron un total de 253.2 millones de kilómetros cuadrados.

El estudio consideró como eventos de amenazas múltiples aquellos en los que coinciden inundaciones y episodios de calor extremo. Usando el método del intervalo de recurrencia promedio, junto con la definición más amplia de peligros, los investigadores encontraron que las zonas del estado con una alta concentración de poblaciones minoritarias estaban expuestas a un mayor riesgo ante este tipo de eventos multiriesgo. Esto sugiere que los métodos más antiguos pueden subestimar tanto la magnitud de los eventos de amenaza múltiple como el impacto desproporcionado en comunidades marginadas, de acuerdo con los investigadores. (AGU Advances, https://doi.org/10.1029/2025AV001667, 2025)

—Rebecca Owen (@beccapox.bsky.social), Escritora de ciencia

This translation by translator Oscar Uriel Soto was made possible by a partnership with Planeteando y GeoLatinas. Esta traducción fue posible gracias a una asociación con Planeteando and GeoLatinas.

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Source: AGU Advances

In 2003, several states and environmental groups sued the U.S. EPA for violating the Clean Air Act by not regulating emissions from new vehicles.

When the case eventually reached the Supreme Court, a group of climate scientists contributed an amicus brief—a legal document in which a third party not directly involved in the case can offer testimony—sharing data demonstrating that rising global temperatures were directly caused by human activity. This led to the Supreme Court deciding that greenhouse gases did constitute pollutants under the Clean Air Act and, ultimately, to the EPA’s 2009 endangerment finding that greenhouse gas emissions endanger human health. The endangerment finding became the basis for governmental regulation of greenhouse gases. Sixteen years later, the Trump administration is poised to repeal it, along with other environmental protections.

In a new commentary, Saleska et al., the authors of the amicus brief, reflect on the brief and the damage the endangerment finding’s potential repeal could cause.

Today, many of the climate scientists’ concerns from the early 2000s have become reality, the authors say. The Earth’s 12 warmest years on record all occurred after 2009. The oceans are growing hotter and more acidic, and Arctic sea ice is retreating. Sea level rise is speeding up—from 2.1 millimeters per year between 1993 and 2003 to 4.3 millimeters per year between 2013 and 2023. Continued warming is also affecting human health. Direct heat-related deaths are on the rise, and so too are wildfires, precipitation extremes such as flooding and drought, climate-enabled spread of disease, and disruptions in agricultural productivity.

The amicus brief authors also note that attribution science, the field that links specific weather events to climate change, has advanced since 2009. Today, they are even more firm in their stance that climate change poses a serious threat to society.

A reversal of the endangerment finding would likely require a lengthy legal process and compelling evidence that climate change does not pose a risk to human health and well-being. But the possibility of a repeal implies a worrying lack of trust in the science and increasing politicalization surrounding climate issues, the authors say. If the role of climate science in policymaking is weakened, it will harm scientific progress and our national well-being, they warn. (AGU Advances, https://doi.org/10.1029/2025AV001808, 2025)

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

Citation: Owen, R. (2025), What’s changed—and what hasn’t—since the EPA’s endangerment finding, Eos, 106, https://doi.org/10.1029/2025EO250219. Published on 24 June 2025.

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Source: Space Weather

The impacts of space weather such as extreme solar winds and magnetic waves are not limited to outer space. Bursts of plasma emanating from the Sun, for instance, can temporarily intensify electric and magnetic fields on the ground when they arrive at Earth, causing geomagnetically induced currents (GICs) to flow into infrastructure such as powerlines, pipelines, and railways. GICs can cause widespread equipment failures, leading to blackouts and safety concerns.

To improve monitoring, modeling, and forecasting of GICs in the United Kingdom, Beggan et al. developed a set of 14 models that better predicts space weather hazards and tracks them in real time, allowing scientists and forecasters to warn operators of critical infrastructure. They also installed three new variometers to measure magnetic field changes at locations across the country. The work was part of the United Kingdom’s Space Weather Instrumentation, Measurement, Modelling and Risk (SWIMMR) program called SWIMMR Activities in Ground Effects, or SAGE.

The SAGE system can estimate changes in the subsurface electric field during geomagnetic storms, then calculate the size of GICs flowing into grounded infrastructure networks—which have known electrical resistance properties—in real time. SAGE also uses real-time data from satellites to predict the probability of magnetic substorms occurring and the magnitude of the storm at different U.K. ground observatory sites.

A major test of the new system occurred in early May 2024, when significant solar activity triggered the largest geomagnetic storm to hit Earth in the past 30 years. SAGE successfully provided real-time information on how the storm was affecting infrastructure. The system also provided two forecasts of GIC magnitude 30 minutes ahead of time; the real-time magnitude that SAGE later identified was between those two predictions.

More work must be done to continue improving SAGE, the authors write. For example, better monitoring of space weather conditions in space and on the ground would provide the system with more robust data on impacts, further improving its prediction capability. (Space Weather, https://doi.org/10.1029/2025SW004364, 2025)

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

Citation: Sidik, S. M. (2025), U.K. space weather prediction system goes operational, Eos, 106, https://doi.org/10.1029/2025EO250229. Published on 23 June 2025.

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Source: Journal of Geophysical Research: Planets

Like Earth, Mars is surrounded by an ionosphere—the part of its upper atmosphere where radiation from the Sun knocks electrons off of atoms and molecules, creating charged particles. The Martian ionosphere is complex and continuously changes over the course of the day, but its role in atmospheric dynamics and radio communication signals means understanding it is key for Mars exploration.

One way to study the Martian ionosphere is with radio occultation, in which a spacecraft orbiting Mars sends a radio signal to a receiver on Earth. When it skims across the Martian ionosphere, the signal bends slightly. Researchers can measure this refraction to learn about Martian ionospheric properties such as electron density and temperature. However, the relative positions of Mars, Earth, and the Sun mean conventional radio occultation cannot measure the middle of the Martian day.

Now, Parrot et al. deepen our understanding of the Martian ionosphere using an approach called mutual radio occultation, in which the radio signal is sent not from an orbiter to Earth but between two Mars orbiters. As one orbiter rises or sets behind Mars from the other’s perspective, the signal passes through the ionosphere and refracts according to the ionosphere’s properties.

The researchers analyzed 71 mutual radio occultation measurements between two European Space Agency satellites orbiting Mars: Mars Express and the ExoMars Trace Gas Orbiter. Thirty-five of these measurements were taken closer to midday than was ever previously achievable, in effect allowing scientists to see a new part of the Martian ionosphere.

The new data enabled the research team to calculate how the ionosphere’s electron density changes throughout the day. They were also able to learn more about how the altitudes of the upper and lower layers of the ionosphere—called M2 and M1, respectively—vary daily. The new data suggest that the peak electron density of the M2 layer changes less dramatically during the day than has been suggested by prior research. The data also show that the M1 does, indeed, still exist during the midday, contradicting previous assumptions.

The researchers also used the new data to calculate ionospheric temperatures. They found that instead of being hottest at midday, temperatures in the ionosphere rise as the Sun reaches Martian sunset. Simulations using a Mars climate model suggest that it is likely winds transporting air, rather than the Sun’s direct heat, that control these temperature dynamics. (Journal of Geophysical Research: Planets, https://doi.org/10.1029/2024JE008854, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), Orbiter pair expands view of Martian ionosphere, Eos, 106, https://doi.org/10.1029/2025EO250228. Published on 20 June 2025.

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Source: Journal of Geophysical Research: Oceans

Submarine canyons around Antarctica tend to have less sea ice, higher sea surface temperatures, and more biomass such as phytoplankton blooms than the shelves they cut into. Phytoplankton blooms feed Antarctic krill, making these canyons an attractive feeding ground for larger predators such as penguins, who make permanent homes for foraging and breeding on the shores surrounding submarine canyons.

Previous studies suggested that, as on a farm, the phytoplankton blooms that attract predators were locally grown, supported by the upwelling of nutrient-rich water. But newer research shows that water moves through the canyon more quickly than phytoplankton can accumulate, so it is likely that currents transport most of the surface biomass into the canyon from other parts of the ocean. Canyons therefore act more like biomass supermarkets, to which food is delivered, than like farms.

McKee et al. examined to what degree phytoplankton grow locally in Palmer Deep canyon on the western Antarctic Peninsula versus being transported in by ocean currents. To do so, they used high-frequency radar to measure ocean currents and satellite imagery taken hours to days apart to measure levels of surface chlorophyll, a proxy for phytoplankton.

The results showed that both processes were occurring. Ocean currents appeared to bring in much of the phytoplankton that flowed on the western side of the canyon, making it more like a supermarket, the researchers write. In contrast, more phytoplankton seem to be growing in place on the eastern flank, making it more like a farm.

The authors also examined how the movement of water correlated to plankton growth, by tracking chlorophyll levels in moving parcels of water. In general, they found that water parcels that saw an increase in phytoplankton levels as they moved through the canyon tended to exhibit more clockwise motion, whereas parcels that saw decreasing phytoplankton levels showed more counterclockwise rotation. (Journal of Geophysical Research: Oceans, https://doi.org/10.1029/2024JC022101, 2025)

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

Citation: Owen, R. (2025), Where do Antarctic submarine canyons get their marine life?, Eos, 106, https://doi.org/10.1029/2025EO250224. Published on 18 June 2025.

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Source: Radio Science

Between 50 and 1,000 kilometers above our heads is the ionosphere, a layer of Earth’s upper atmosphere consisting of charged particles: ions (atoms that have gained or lost a negatively charged electron) and loose electrons. The ionosphere alters the path of electromagnetic waves that reach it, including radio and GPS signals, so studying it is helpful for understanding communication and navigation systems.

One way to study the ionosphere is to “nudge” it with powerful radio waves sent from the ground to see how it reacts. Where the waves hit the ionosphere, they temporarily heat it, changing the density of charged particles into irregular patterns that can be detected from the way they scatter radio signals. By studying these irregularities, known as artificial periodic inhomogeneities (APIs), scientists can learn more about the ionosphere’s composition and behavior.

However, factors such as space weather and solar activity can inhibit both the formation and detection of APIs. La Rosa and Hysell sought to enhance the reliability and utility of the API research technique by examining API formation in all three main regions of the ionosphere, the D, E, and F regions. Past techniques focused only on API formation in the E region.

To do so, the researchers revisited data from research conducted in April 2014 at the High-frequency Active Auroral Research Program (HAARP) facility in Alaska. HAARP’s radio transmitters created small perturbations in the ionosphere, and the facility’s receivers captured the resulting scattered radio signals.

Initial analysis of the 2014 data revealed some APIs in the E region, but this team of researchers reprocessed the data at higher resolution. This reanalysis allowed them to document, for the first time, simultaneous APIs across all three regions, all triggered by a single radio nudge.

API formation in each of the three regions is dictated by a different set of mechanisms, including chemical interactions, heating effects, and forces that change the density of charged particles; this variability has made it difficult to develop a stand-alone model of API formation across the ionosphere.

To address that challenge, the researchers extended a model previously created to capture API formation in the E region by incorporating the relevant mechanisms for the D and F regions. In simulation tests, the model successfully reproduced the behavior observed in all three regions. This model could help deepen understanding of the physics at play in the ionosphere. (Radio Science, https://doi.org/10.1029/2025RS008226, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), Nudging Earth’s ionosphere helps us learn more about it, Eos, 106, https://doi.org/10.1029/2025EO250222. Published on 17 June 2025.

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Source: Paleoceanography and Paleoclimatology

Great apes began to diverge from other primates around 25 million years ago, according to eastern African fossil records. Though it would take another 20 million or so years for upright-walking hominins to appear, understanding the habitats of early apes helps clarify how environments drove the evolution of our distant ancestors.

Munyaka et al. excavated and analyzed fossils from an approximately 20-million-year-old early Miocene site in western Kenya called Koru 16. The now-extinct Tinderet Volcano repeatedly blanketed the area in ash, preserving it for millions of years, and today, the site hosts fossils from an array of plants and animals.

Many prior studies focused on the area around Koru 16: The first primate fossils from the site were discovered in 1927, and famed anthropologist Louis Leakey led multiple digs there.

As part of the new research, scientists uncovered fossils of approximately 1,000 leaves and many vertebrates at two subsites between 2013 and 2023. The specimens included those of a new type of large-bodied ape and two other previously known ape species, bringing the total number of vertebrate species discovered at the site to 25.

By examining the shapes of fossilized leaves, the geochemistry of fossilized soils (paleosols), and the distribution and density of fossil tree stumps, the researchers determined that the Koru 16 site was likely located within a warm, wet forest, with rainfall amounts similar to those of modern-day tropical and seasonal African forests. However, the ancient ecosystem likely hosted more deciduous plants than do modern tropical forests. The vertebrate fossils the researchers analyzed were consistent with apes, pythons, and rodents that might have lived in such an environment.

The researchers suggest that this ancient forest environment—which was interspersed with open areas and frequently disturbed by fires, floods, or volcanic eruptions—played a role in shaping the course of evolution for early apes. (Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2025PA005152, 2025)

—Madeline Reinsel, Science Writer

Citation: Reinsel, M. (2025), Early apes evolved in tropical forests disturbed by fires and volcanoes, Eos, 106, https://doi.org/10.1029/2025EO250221. Published on 12 June 2025.

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Source: AGU Advances

As the global climate continues to warm, fire seasons have intensified, and large-scale wildfires have become more frequent in many parts of the world. Factors such as vegetation type, land use patterns, and human activity all affect the likelihood of ignition, but wildfire proliferation ultimately depends on two factors: climate and fuel availability.

Kampf et al. studied relationships between fire, fuel, and climate in temperate regions around the world, focusing specifically on western North America, western and central Europe, and southwestern South America. Each of the three regions includes desert, shrub, and forest areas, as well as local climates ranging from arid to humid.

The researchers pulled information on total burned area and wildfire frequency in these regions between 2002 and 2021 from the GlobFire database, and they sourced data on land cover and biomass during the same period from NASA’s Global Land Cover Mapping and Estimation (GLanCE). They also used precipitation and evapotranspiration data from TerraClimate to calculate the mean annual aridity index (mean annual precipitation divided by mean annual evapotranspiration) for each region.

The researchers found that over the 20-year study period and across all three regions, fires burned smaller areas of land in zones with either very dry climates or very wet climates compared with zones of intermediate aridity. They suggest that this trend is explained by the lack of vegetation sufficient to fuel widespread fires in dry zones and, in wet zones, by weather conditions that dampen the likelihood of fires. In contrast, burned areas were larger in the intermediate zones where biomass abundance and weather conditions are more conducive to fueling fires.

Of the three regions studied, North America had the largest total burned area, fraction of area burned, and fire sizes. The researchers note that the fragmentation of vegetated areas in South America (by the Andes Mountains) and in Europe (because of extensive land use) has likely limited the sizes of fires and burned areas in those regions. They also point out that rising temperatures and aridity are increasing the risk of large wildfires in all three regions, suggesting that fire managers need to be flexible and responsive to local changes. (AGU Advances, https://doi.org/10.1029/2024AV001628, 2025)

—Sarah Derouin (@sarahderouin.com), Science Writer

Citation: Derouin, S. (2025), The Goldilocks conditions for wildfires, Eos, 106, https://doi.org/10.1029/2025EO250215. Published on 9 June 2025.

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Source: GeoHealth

Wildfires are creeping into urban environments with alarming frequency, and they are connected to health problems ranging from respiratory illnesses to hypertension to anxiety. Studying the links between wildfires in these areas and health is challenging because wildfire smoke and ash contain a mix of chemicals from buildings, cars, and electronics, leaving researchers and communities with many unanswered questions.

Barkoski et al. recently published the GeoHealth Framework for Wildland Urban Interface Fires to help researchers quickly visualize the relationships between urban wildfires and health outcomes, as well as identify data gaps and future research priorities. It also aims to improve the coordination among different groups working to support wildfire preparedness, response, and recovery. The researchers built the framework using the example of the 2020 Walbridge Fire, which burned more than 55,000 acres (about 22,258 hectares) in Sonoma County, California. This example helped them understand the types of geoscience and health data that are available and that are needed after a wildland-urban interface fire.

To apply the framework, users define a question and then map various wildfire and health factors and the ways they are connected. For example, they may select environmental factors preceding a specific fire, such as land use and recent weather patterns; characteristics of the fire, including its size and the kinds of materials it burned; and factors that influenced its spread, such as firefighter response, wind, and topography. The team suggests pulling data from sources such as the U.S. Geological Survey, NASA, NOAA, EPA, electronic health records, and public surveys.

These inputs and the known and hypothesized connections among them help users to identify which pollutants a fire may generate, how humans may encounter these pollutants (such as through the air or drinking water), and how these encounters may affect the likelihood of physical or mental health consequences.

The researchers also note that the framework can be expanded and adapted to apply to new research questions. For instance, if researchers want to better understand how wildfire exposure affects the biological mechanisms of disease, they could incorporate epidemiological, toxicological, and clinical research studies into the framework. These studies might include more detailed information about how wildfire smoke harms health, such as gene variants that predispose people to asthma. (GeoHealth, https://doi.org/10.1029/2025GH001380, 2025)

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

Citation: Sidik, S. M. (2025), Charting a path from fire features to health outcomes, Eos, 106, https://doi.org/10.1029/2025EO250214. Published on 5 June 2025.

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Source: Geophysical Research Letters

This is an authorized translation of an Eos article. 本文是Eos文章的授权翻译。

土壤湿度是温度和湿度的关键调节器，易受气候变化的显著影响。尽管土壤湿度至关重要，但其建模工作涉及数十个约束不充分的参数，而且不同的模型对土壤湿度水平在全球变暖背景下的变化往往存在分歧。

Gallagher 和 McColl 采取了一种“极其简化”的方法，仅根据降水量和地表净辐射来模拟土壤湿度。该模型在使用欧洲中期天气预报中心第五代大气再分析数据(ERA5) 和第六次耦合模式比较计划(CMIP6) 气候数据集进行测试时，效果良好。

研究人员表示，这令人惊讶，因为这个简单的模型排除了近期许多文献关注的测量数据：水汽压差（空气能够容纳的水分量与实际容纳的水分量之间的差值）和大气二氧化碳 (CO2) 水平。预计这两者都将随着温室气体排放的增加而上升。

研究人员认为，他们的模型之所以仍然有效，是因为水汽压差无法准确衡量大气对水的需求；而模型中包含的地表净辐射才是更佳的衡量指标。关于二氧化碳，研究人员表示，之前的一些研究高估了这种气体的作用。

这个简单的模型为两个关于土壤湿度的基本问题提供了可能的答案：(1)为什么土壤湿度呈W型纵向剖面，赤道和两极的湿度高，两极之间的湿度低；(2)为什么土壤湿度在某些地区随温度升高而增加，而在另一些地区则降低？

W型分布可能是降水率和辐射强度共同作用的结果。赤道附近的高降水量在模型中占主导地位，并导致高土壤湿度。中纬度地区和两极地区的降水量都处于中等水平。但中纬度地区比两极地区接收到更强烈的辐射，导致中纬度地区的土壤相对干燥。

至于第二个问题，研究人员认为，气候变暖可能对土壤湿度有不同的影响，因为气候变暖既可能伴随降水增加（导致土壤湿度升高），也可能伴随地表净辐射增加（导致土壤湿度降低）。这两个变量在不同地区会以不同的程度相互抵消，这意味着气候变暖有时会提高土壤湿度，有时则会降低土壤湿度。(Geophysical Research Letters, https://doi.org/10.1029/2025GL115044, 2025)

—科学撰稿人Saima May Sidik (@saimamay.bsky.social)

This translation was made by Wiley. 本文翻译由Wiley提供。

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Source: AGU Advances

Shortly after President Joe Biden took office in 2021, he nominated Asmeret Asefaw Berhe, then a biogeochemist at the University of California, Merced, to oversee the Department of Energy’s (DOE) Office of Science. After a 15-month vetting process involving interviews, a mountain of paperwork, and, ultimately, a Senate confirmation, the AGU medalist became the first person of color and the first Earth scientist to hold the position. She served in the position for just under 2 years.

Now, with science and diversity programs under attack, she reflects on her path to leadership in a new commentary in AGU Advances. Berhe became familiar with DOE’s science program as a graduate student at the University of California, Berkeley. She later went on to receive DOE funding, collaborate with researchers from various national laboratories, and mentor scientists who went on to secure DOE positions. She says that combined with guidance from her mentors, these experiences helped her develop the skills she needed for her DOE appointment, not only in science but in managing, accounting, mediation, and ethical guidance.

Berhe, who was born in Eritrea and was one of only a few undergraduate women at Asmara University studying soil science, prioritized basic research, robust science communication, and promoting diversity in STEM (science, technology, engineering, and mathematics) in her DOE role. Providing opportunities in STEM for people from all walks of life starts with equalizing the distribution of funding, she writes. She cited an American Physical Society report that found, in 2018, 90% of federal research funding went to the top 22% of institutions, even though the vast majority of students—especially those from low-income backgrounds—attend other schools. Under Berhe’s tenure, the DOE began asking grant applicants to demonstrate plans for collaborating with schools less likely to receive funding, enabling scholars from diverse backgrounds to access DOE resources.

Berhe thinks recent efforts by some politicians to end diversity, equity, and inclusion (DEI) programs are partly because of a misconception around what DEI means. These programs are often misconstrued as serving only gender or racial minorities from urban environments, when, in fact, many are intended to serve a much wider range of Americans, she writes.

Today’s political climate sometimes leaves Berhe with feelings of despair. But she remains hopeful that with time, the next generation of scientists will benefit from opportunities like those she’s had. “Together, we will weather this storm,” she writes. (AGU Advances, https://doi.org/10.1029/2025AV001757, 2025)

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

Citation: Sidik, S. M. (2025), Former Department of Energy leader reflects on a changing landscape, Eos, 106, https://doi.org/10.1029/2025EO250211. Published on 4 June 2025.

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Source: AGU Advances

In the southern flanks of the Indian Ocean and the central and eastern Pacific, just north of the Antarctic Circumpolar Current, lie the Subantarctic Mode Waters. As part of the global ocean conveyor belt, these large masses of seawater transfer substantial amounts of heat and carbon northward into the interiors of the Indian and Pacific Oceans. These waters hold about 20% of all anthropogenic carbon found in the ocean, and their warming accounted for about 36% of all ocean warming over the past 2 decades—making them critical players in Earth’s climate system.

Prior research has suggested Subantarctic Mode Waters form when seawater flowing from warm, shallow subtropical regions mixes with water flowing from cold, deep Antarctic regions. But the relative contributions of each source have long been debated.

Fernández Castro et al. used the Biogeochemical Southern Ocean State Estimate model to investigate how these water masses form. The model incorporates real-world physical and biogeochemical observations—including data from free-roaming floats—to simulate the flow and properties of seawater. The researchers used it to virtually track 100,000 simulated particles of water backward in time over multiple decades to determine where they came from before winding up in Subantarctic Mode Waters.

The particle-tracking experiment confirmed that subtropical and Antarctic waters indeed meet and mix in all areas where Subantarctic Mode Waters form but offered more insight into the journeys and roles of the two water sources.

In the Indian Ocean, the simulations suggest, Subantarctic Mode Waters come mainly from warm, shallow, subtropical waters to the north. In contrast, in the Pacific Ocean, Subantarctic Mode Waters originate primarily from a water mass to the south known as Circumpolar Deep Water.

Along their southward flow to the subantarctic, subtropical waters release heat into the atmosphere and become denser, while ocean mixing reduces their salinity. Meanwhile, the cooler Circumpolar Deep Water absorbs heat and becomes fresher and lighter as it upwells and flows northward from the Antarctic region to the subantarctic.

These findings suggest that Subantarctic Mode Waters affect Earth’s climate differently depending on whether they form in the Indian or Pacific Ocean—with potential implications for northward transport of carbon and nutrients. Further observations could help confirm and deepen understanding of these intricacies. (AGU Advances, https://doi.org/10.1029/2024AV001449, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), On the origins of Subantarctic Mode Waters, Eos, 106, https://doi.org/10.1029/2025EO250207. Published on 2 June 2025.

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Source: Journal of Geophysical Research: Oceans

The Atlantic Meridional Overturning Circulation (AMOC) serves as the Atlantic Ocean’s conveyor belt, transporting warm water north toward the Arctic Circle and returning cold, dense water back to the tropics. Nearshore areas off Greenland are critical sites in AMOC, influencing the redistribution of heat and nutrients around the world.

The continental shelf along Greenland’s coast is marked by deep grooves called glacial troughs that extend from the mouths of glacially carved fjords to the open ocean. Research in Antarctica suggests glacial troughs there enhance the mixing of cold and warm waters, but few observations have been collected to determine whether the same is true of Greenland’s troughs.

Aboard R/V Neil Armstrong in late summer 2022, as part of an Overturning in the Subpolar North Atlantic Program cruise funded by the National Science Foundation, Nelson et al. explored how troughs influence ocean circulation around Greenland. They collected data in southwestern Greenland at the Narsaq Trough, which is 30 kilometers wide at its mouth and reaches 600 meters at its deepest point—about 4 times deeper than the average surrounding continental shelf. Gathering measurements along multiple ship tracks allowed the researchers to compare water mass properties in and outside the trough, describe flows in and around it, and estimate the mixing of waters with different temperatures and nutrient concentrations.

The results showed that the Narsaq Trough provides a pathway for warm, salty Atlantic Water to intrude onto the continental shelf and mix with cold, fresh polar waters. Consequently, waters in the trough are fresher, richer in oxygen, less rich in nutrients, and sometimes colder than nearby offshore waters. These changes in water conditions may slightly limit melting of glacial ice in the adjacent fjord. Furthermore, the trough creates subsurface circulation that likely exports the modified water from the trough, which may increase stratification and decrease deepwater formation off the continental shelf.

The study offers new insights into Greenland’s understudied glacial troughs and their role in modulating the climate system, the authors say. They note, however, that more work is needed to establish the troughs’ cumulative effects on global ocean circulation. (Journal of Geophysical Research: Oceans, https://doi.org/10.1029/2024JC022246, 2025)

—Aaron Sidder, Science Writer

Citation: Sidder, A. (2025), How Greenland’s glacial troughs influence ocean circulation, Eos, 106, https://doi.org/10.1029/2025EO250205. Published on 29 May 2025.

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Source: Geophysical Research Letters

In the Atlantic Ocean, a system of currents carries vast amounts of warm, salty surface water northward. As this water reaches higher latitudes and becomes colder, it sinks and joins a deep, southward return flow. This cycle, known as the Atlantic Meridional Overturning Circulation (AMOC), plays an important role in Earth’s climate as it redistributes heat, nutrients, and carbon through the ocean.

Although scientists know that the strength of the AMOC—meaning how much water it transports—can vary over time and across regions, it has been unclear how changes in AMOC strength at high northern latitudes may or may not be linked to changes farther south.

Petit et al. applied high-resolution climate modeling to uncover connections between AMOC variability at the midlatitude of 45°N and the current’s behavior at higher subpolar latitudes. High-latitude AMOC observations used in the modeling were captured by the Overturning in the Subpolar North Atlantic Program (OSNAP) instrument array, a network of moorings and submersibles deployed across the Labrador Sea between Greenland and Scotland.

The researchers discovered that subpolar AMOC strength, as captured by OSNAP data, does not affect midlatitude AMOC strength. However, they did find that the density of the subpolar AMOC water beginning its journey back southward affected subsequent midlatitude AMOC strength.

Changes in the water’s density at high latitudes appear to be driven by changes in atmospheric pressure that affect wind stress and buoyancy at the sea surface. The team’s analysis indicates that within a time span of 1 year, these subpolar density changes propagate southward along the far western side of the North Atlantic, creating a steeper density gradient at midlatitudes and, ultimately, affecting AMOC strength there.

The findings suggest that OSNAP density measurements could be used to monitor midlatitude AMOC strength. The study’s results could also help inform the design of future ocean-observing systems to deepen understanding of the ocean’s role in Earth’s climate, according to the researchers. (Geophysical Research Letters, https://doi.org/10.1029/2025GL115171, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), Water density shifts can drive rapid changes in AMOC strength, Eos, 106, https://doi.org/10.1029/2025EO250202. Published on 28 May 2025.

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Source: Global Biogeochemical Cycles

Marine life plays a pivotal role in Earth’s carbon cycle. Phytoplankton at the base of the aquatic food web take up carbon dioxide from the atmosphere, convert it to organic carbon, and move it around as they become food for other organisms. Much of this carbon eventually returns to the atmosphere, but some ends up sequestered in the deep ocean via a process called carbon export.

Quantifying carbon export to the deep ocean is critical for understanding changes in Earth’s climate. Measurements in the Southern Ocean, a key region for global ocean circulation and a substantial carbon sink, are especially important but have been sparse, particularly in areas with sea ice that are difficult to access.

To address that gap, Liniger et al. used data from 212 autonomous, floating instruments known as Biogeochemical-Argo (BGC-Argo) floats to estimate carbon export across the Southern Ocean basin. These floats roam the upper 2,000 meters of the ocean, can travel beneath sea ice, and are equipped with sensors that measure physical and biogeochemical properties of seawater.

Though prior studies have used BGC-Argo data to estimate Southern Ocean carbon export, most focused on narrow regions or timescales and excluded sea ice–covered areas. The new analysis uses data collected between 2014 and 2022 by floats scattered across the entire ocean basin, including under sea ice. After developing a novel method to calculate carbon export using the floats’ measurements of sinking particulate organic carbon and dissolved oxygen change over time, the researchers estimated that about 2.69 billion tons of carbon sink to the deep sea each year in the Southern Ocean.

Their findings also suggest that carbon export varies significantly in different parts of the Southern Ocean, with only about 8% occurring in seasonally ice-covered areas. But the researchers say more investigation is needed to clarify the role of the highly active ecosystems in the sea ice zone, especially as climate change drives shifts in sea ice dynamics. (Global Biogeochemical Cycles, https://doi.org/10.1029/2024GB008193, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), Robotic floats quantify sinking carbon in the Southern Ocean, Eos, 106, https://doi.org/10.1029/2025EO250193. Published on 27 May 2025.

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