Team investigates significance of newly discovered hydrothermal fields off the island of Milos

MARUM - Center for Marine Environmental Sciences, University of Bremen

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Sampling fluids of 180 degree Celsius at the White Sealhound structure. Photo: MARUM – Center for Marine Environmental Sciences, University of Bremen

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Credit: MARUM – Center for Marine Environmental Sciences, University of Bremen

The study identifies three major vent areas — Aghia Kiriaki, Paleochori–Thiorychia, and Vani — all located along active fault zones that run across the Milos shelf. These faults belong to a large tectonic depression, the Milos Gulf–Fyriplaka graben, which has lowered the seafloor to depths of up to 230 meters. The close alignment of vents with these geological structures shows that tectonic activity plays a key role in determining where hydrothermal venting occurs.

“We never expected to find such a large field of gas flares off Milos,” says Solveig I. Bühring, senior author of the study and scientist at the MARUM – Center for Marine Environmental Sciences, University of Bremen, who led the expedition M192 during which the vents were discovered. “When we first observed the vents through the ROV cameras, we were stunned by their diversity and beauty — from shimmering, boiling fluids to thick microbial mats covering the chimneys.”

According to first author Paraskevi Nomikou of the National and Kapodistrian University of Athens, the spatial pattern of these vent clusters is closely controlled by the island’s tectonic fabric:

“Our data clearly show that the gas flares follow the patterns of the major fault systems around Milos,” Nomikou explains. “Different fault zones influence different vent clusters, especially where several faults meet. These tectonic structures strongly control how and where hydrothermal fluids reach the seafloor.”

The findings demonstrate how active faulting and ongoing geological processes have shaped the evolution of these vent fields. This discovery establishes Milos as one of the most significant natural laboratories in the Mediterranean for studying the interplay between tectonics, volcanism, and hydrothermal activity.

The results are also relevant for the MARUM-based Cluster of Excellence “The Ocean Floor – Earth's Uncharted Interface.” A follow-up expedition to Milos, the Kolumbo submarine volcano off Santorini, and Nisyros is planned. The research is the result of close collaboration between Greek and German institutions, including the National and Kapodistrian University of Athens, MARUM – University of Bremen, Friedrich-Alexander-Universität Erlangen-Nürnberg, ICBM – Institute for Chemistry and Biology of the Marine Environment Oldenburg, and Constructor University Bremen.

Original publication:

Paraskevi Nomikou, Konstantina Bejelou, Andrea Koschinsky, Christian dos Santos Ferreira, Dimitrios Papanikolaou, Danai Lampridou, Stephanos P. Kilias, Eirini Anagnostou, Marcus Elvert, Clemens Röttgen, Joely M. Maak, Alissa Bach, Wolfgang Bach, Areti Belka, Evgenia Bazhenova, Karsten Haase, Charlotte Kleint, Effrosyni Varotsou, Palash Kumawat, Erika Kurahashi, Jianlin Liao, Eva-Maria Meckel, Ignacio Pedre, Wiebke Lehmann, Enno Schefuß, Michael Seidel, Sotiria Kothri & Solveig I. Bühring: Structural control and depth clustering of extensive hydrothermal venting on the shelf of Milos Island. Scientific Reports volume 15 (2025). DOI: https://doi.org/10.1038/s41598-025-26398-y

Contact:

Dr. Solveig I. Bühring
Petrology of the Ocean Crust
MARUM – Center for Maine Environmental Sciences, University of Bremen
Email: sbuehring@marum.de

 

Participating institutions:

• Department of Geology and Geoenvironment, National and Kapodistrian University of Athens (Greece)
• School of Science, Physics & Earth Sciences, Constructor University Bremen, Germany
• Faculty of Geosciences, University of Bremen
• MARUM – Center for Marine Environmental Sciences, University of Bremen
• GeoZentrum Nordbayern, Friedrich-Alexander-University Erlangen-Nuernberg
• ICBM – Institute for Chemistry and Biology of the Marine Environment, Carl Von Ossietzky University of Oldenburg

 

MARUM produces fundamental scientific knowledge about the role of the ocean and the seafloor in the total Earth system. The dynamics of the oceans and the seabed significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, resulting in the creation of unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society, the marine environment, and in accordance with the sustainability goals of the United Nations. It publishes its quality-assured scientific data to make it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperation with companies and industrial partners is carried out in accordance with its goal of protecting the marine environment.

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Journal

Scientific Reports

DOI

10.1038/s41598-025-26398-y 

Article Title

Structural control and depth clustering of extensive hydrothermal venting on the shelf of Milos Island

 

Arkansas research awarded for determining cardinal temps for eight cover crops

New information offers better guidance for cover crop growth models

University of Arkansas System Division of Agriculture

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Research at the Arkansas Agricultural Experiment Station determined the cardinal temperatures — base, optimal and maximum — of eight cover crops, including crimson clover.

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Credit: U of A System Division of Agriculture photo by Mila Pessotto

FAYETTEVILLE, Ark. — Knowing what temperatures that a plant can withstand is a hallmark of botanical science, but those temperatures had not been well documented for many cover crops.

Grown in periods of the year when the cash crop is absent, cover crops are planted for erosion control, as well as weed suppression and to improve soil structure, moisture retention and nutrient cycling. They also provide habitat for beneficial insects and can serve as forage for farm animals.

Without knowledge of the cover crops’ base, optimal and maximum temperature ranges —known as cardinal temperatures — agricultural scientists could not develop accurate plant growth and biomass prediction models, which help farmers optimize decisions like when to terminate the cover crop. The models also help assess weed suppression, estimate nutrient cycling and quantify the benefits of soil carbon and potential negative impacts of a cover crop.

A team of researchers with the University of Arkansas System Division of Agriculture, led by Trent Roberts, professor of soil fertility and soil testing and Endowed Chair in Soil Fertility Research in the crop, soil and environmental sciences department, took on the problem by evaluating eight commonly grown cover crop species in growth chambers to find their cardinal temperatures.

The base temperature is the lowest temperature at which the plant will still exhibit a measurable growth rate. Optimal is where plant growth is at its peak, and maximum is the temperature at which plant growth ceases due to excessive heat. For many plant species, the relationship between temperature and growth rate or developmental stage can be correlated and predicted using mathematical models. 

Not only did the researchers identify the base temperatures for two cover crop species and the optimum temperatures for three of the eight cover crop species for the first time, they also determined the maximum temperature values of all eight cover crops, which included crimson clover, Austrian winter pea, balansa clover, barley, black-seeded oats, common vetch, cereal rye, crimson clover and hairy vetch.

Estimates were required for maximum temperatures of five of the cover crop species due to the 34 Celsius upper limits of the growth chamber. Although maximum temperatures may not be as critical for growth modeling as the base and optimum temperatures, the researchers pointed out that knowledge of the maximum temps may be more crucial in the Mid-South and Southern states, where temperatures can rise quickly in late winter and early spring.

In all, they offered 14 newly identified cardinal temperatures for the eight cover crop species. Five cardinal temperatures determined in the study were different from what was previously recorded and three of the base temperature values were found to differ from previously reported values, including cereal rye, which was almost 9 degrees Celsius lower than the previously reported value in the scientific literature.

“Such a large difference in base temperature values would lead to gross underestimations of plant growth and development for cereal rye when using the data reported in the literature," said Roberts, whose role includes research and outreach work through the Division of Agriculture’s Arkansas Agricultural Experiment Station and Cooperative Extension Service.

Mila Pessotto, Ph.D., was the lead author of the research article titled “Determining Cardinal Temperatures for Eight Cover Crop Species” as a masters student in the crop, soil and environmental sciences department of the Dale Bumpers College of Agricultural, Food and Life Sciences at the University of Arkansas.

“The refinement or identification of 18 of the 24 possible cardinal temperatures investigated in this study generates a significant step forward in the ability to model cover crop species growth and development,” Pessotto said.

Tri Societies Recognition

The work, originally published in 2023, recently earned Pessotto and her collaborators a 2025 Outstanding Paper Award from the American science societies for crop, soil and agronomy.

The American Society of Agronomy, the Crop Science Society of America, and the Soil Science Society of America — also known as the Tri Societies — recognize outstanding publications from their journals each year based on advancement of knowledge in the profession, effectiveness of communication, methodology, originality and impact.

Co-authors of the study included Roberts, Mary Savin, professor and horticulture department head, Matt Bertucci, assistant professor of sustainable fruit and vegetable production in the horticulture department, Jeremy Ross, professor and extension soybean agronomist, and Caio dos Santos, who received a master’s degree from the University of Arkansas in 2020.

Pessotto is now a postdoc research associate in the department of agronomy at Iowa State University, where dos Santos also recently earned his doctorate.

The study was supported with funding and technical assistance from the Arkansas Corn and Grain Sorghum Board and the Arkansas Soybean Promotion Board.

To learn more about the Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website. Follow us on X at @ArkAgResearch, subscribe to the Food, Farms and Forests podcast and sign up for our monthly newsletter, the Arkansas Agricultural Research Report. To learn more about the Division of Agriculture, visit uada.edu. Follow us on X at @AgInArk. To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit uaex.uada.edu.

About the Division of Agriculture

The University of Arkansas System Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system. 

The Division of Agriculture is one of 20 entities within the University of Arkansas System. It has offices in all 75 counties in Arkansas and faculty on three system campuses.  

Pursuant to 7 CFR § 15.3, the University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services (including employment) without regard to race, color, sex, national origin, religion, age, disability, marital or veteran status, genetic information, sexual preference, pregnancy or any other legally protected status, and is an equal opportunity institution.

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DOI

10.1002/agg2.20393 

Peace without prosperity: Angola marks 50 years of independence

Angola declared its independence from Portugal on 11 November, 1975. But in a country where the majority of the population was born long after this date, the celebrations give rise to a question: what does it mean to be free when it has failed to bring the promised prosperity?


Issued on: 11/11/2025 - RFI

Young people in Angola protest against poverty, inequality and violations of the rule of law, Luanda, 23 November, 2024. © Julio Pacheco Ntela / AFP

The promises made in 1975 painted a picture of an egalitarian state, capable of repairing five centuries of domination and transforming political freedom into social justice.

The Angola of 2025 is rich in natural resources, including oil, gas and diamonds. Its capital, Luanda, is dotted with steel and glass towers Almost 70 percent of its 37 million inhabitants are under 30 – a dynamic, urban population.

However, the United Nations Human Development Index ranks the country 148th out of 193. Despite significant progress since the end of the civil war in 2001, the gap between the promised land and the reality remains – with a lack of infrastructure, poor housing amongst the capital's skyscrapers and a generation of frustrated youth.

Death toll rises in Angola after protests and looting over fuel hike

President João Lourenço, elected in 2017 following José Eduardo dos Santos's 38-year reign, likes to remind the people that "independence is not an end point, but an ongoing endeavour".

Under his leadership, the country has been attempting to turn the page on its authoritarian past, and its economy's total dependence on oil – the revenues from which fund more than 80 percent of the state budget.

Angola left OPEC, the intergovernmental body of oil-producing nations, at the end of 2023 in order to regain control of its production. It is investing in gas and agricultural diversification, as well as building the multi-billion dollar Lobito Oil Refinery led by the state oil company, Sonangol.

Completion is expected by early 2027, when it will process 200,000 barrels of crude oil per day, with the aim of making Angola a major exporter of refined products to both domestic and regional markets.

A marginalised majority

The young people who make up the majority of the Angolan population have known neither the war of independence nor the civil war. But while they may not have inherited the hardships of the past, they face another struggle: against unemployment, poverty and political mistrust.

Despite two decades of peace, economic development remains fragile. Access to stable employment is rare, especially for graduates. "The problem is no longer war, but the distribution of wealth and economic freedom," says economist Francisco Paulo.

According to him, Angola's labour market remains dominated by the informal economy: "Of 12 million workers, 10 million work in the informal sector. That represents more than 80 percent of jobs, a real social time bomb."

Young people alternate between odd jobs, street trading and long periods of inactivity. The dominance of the oil economy has led to a lack of diversification of opportunities. Growth benefits a minority, while inequalities are widening.

How Portugal's Carnation Revolution changed the fate of its colonies in Africa

Meanwhile, the relationship between citizens and the state remains marked by mistrust.

Activist Laura Macedo describes a climate of silent tension: "Citizens fear those in power, and those in power fear citizens. This mutual fear ultimately leads to revolt."

She highlights a generational shift, saying: "Those who govern us can no longer threaten us with war. It no longer silences us."

For her, this symbolises the breaking of a cycle: war is no longer a political argument. But freedom of expression remains fragile, limited by the authorities, the police and societal pressures.

Transition to true democracy

For philosopher and activist Domingos da Cruz, a leading figure in the 15+2 human rights group, the country remains trapped by an authoritarian culture. "Fifty years after independence, we cannot talk about freedom, only resistance," he says.

He believes that the transition to true democracy "will depend exclusively on the Angolan people".

The 15+2 name was coined when 15 young activists and two other individuals were arrested – da Cruz among them – for discussing a book on non-violent resistance to the regime under dos Santos.

Their trial represented a turning point in the country's recent political history. For the first time, a civil protest led by young urbanites was expressed peacefully, without resorting to violence. Following this event, several citizen movements emerged in the fight against corruption, unemployment and electoral transparency.

Artistic exchange between Brazil and Angola aims to reclaim colonial ties

'Women are relegated'

Inequalities in the country are visible as early as primary school. Nearly 4 million children remain excluded from the education system, according to local NGOs. Activist Sizaltina Cutaia says there is a persistent hierarchy: "Young people simply want to live in a country where they can fulfil their potential, without having to join a political party."

She added: "Education should be the starting point, but girls are still often excluded, especially in poor families. The belief persists that they will be supported by a husband."

This lack of access to schooling further fuels inequality and undermines social mobility, and despite a growing presence in public life, women remain marginalised. Those active in politics face verbal abuse and media invisibility.

"The history of Angola is told through the figure of the father of the nation. Women, despite being active participants in the struggle, are relegated to the margins," says Cutaia.

Macedo too highlights institutionalised patriarchy. "The president said he would put women in government, and that he would put more in if they behaved themselves. That sums up the prevailing mindset."

The promise of equality from 1975 has not been fulfilled, and nor have the pledges of prosperity. Fifty years after Angola's first president, Agostinho Neto, declared independence, the country no longer lives under fire, but under the weight of disillusionment.

This article was adapted from the original version in French by Ligia Anjos.

 

Decoding dangers of Arctic sea ice with seismic, radar method

As drifting sea ice menaces coastal communities, a tool from researchers at Penn State lends new insight

Penn State

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Sea ice was visible in the Arctic Ocean along the coast of Utqiaġvik, Alaska, on Aug. 2, 2024. A tool developed by researchers at Penn State identifies seismic activities linked to different types of shifting ice. 

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Credit: Provided by Gabriel Rocha Dos Santos

UNIVERSITY PARK, Pa. — Sea ice coverage in the Arctic Ocean is at one of its lowest levels on record, yet there’s no unanimity on when that ice will disappear completely during summer months. Understanding the traits and movements of the remaining ice is a persistent challenge for scientists, but a study by researchers at Penn State has provided a new tool to explore ice characteristics and interactions along with coastal conditions. Using radar images, fiber-optic sensing and seismic sensors, the team in the College of Earth and Mineral Sciences (EMS) identified different seismic activities linked to the types of ice that are shifting.

The work was published in the journal Geophysical Research Letters.

Drifting sea ice threatens Arctic communities, including infrastructure, as it can crash into stable formations that underpin where people live and work.

The new method can help coastal communities understand the scope, strength and hazards of these ice movements during different seasons, said Tieyuan Zhu, associate professor of geosciences and corresponding author on the study.

“This work creates a foundation to assess threats from particular kinds of sea ice that drift at different times of year,” said Zhu, who is also affiliated with the EMS Energy Institute. “April tends to see smaller but more chunks of ice. In January, they tend to be the strongest.”

Zhu and Gabriel Rocha Dos Santos, doctoral candidate in geosciences and the first author on the paper, centered their study near Utqiaġvik, a town with a population of about 4,900 in northern Alaska. The region is known informally as the land of fast ice — a reference to landfast ice that attaches to the ground as smaller sea ice travels on wind and ocean currents. The researchers collected seismic and radar data from two large interactions of chunks of sea ice striking landbound, stationary ice — one each on Jan. 4, 2022, and April 8, 2022.

To determine seismic activity during the strikes, the team used data from two mechanisms: broadband seismometers that capture ground motion and fiber-optic cables laid across the tundra. The latter employed acoustics to record longer-distance seismic patterns. Merging the insights with radar-derived visual observations allowed researchers to identify different types of ice-to-ice impacts and associate them with distinct seismic tremors.

The team said they believe those tremors can help reveal traits and threats posed by shifting sea ice where conventional monitoring is limited by harsh Arctic conditions. During the April 2022 event, tremors generated by smaller ice chunks were more intermittent and short-lived despite robust overall ice cover. Three months earlier, when large, more dense ice packs accumulated, the researchers found harmonic tremors, or more constant vibrations.

Zhu described the findings as the first evidence linking types of Arctic ice — and individual ice interactions — to specific seismic signals. Converting the seismic data to audio gave researchers an alternative way to interpret, understand and share the seismic activity in tandem with radar images.

“We could hear the vibration, the tremor,” Dos Santos said. “It’s a very eerie sound when you speed up the recordings to 200 times the ice’s actual rate of movement.”

Accelerating playback helps distinguish variations in ice friction and gliding, which happen over hours-long periods, the researchers said. Some lower-frequency recordings in April 2022 appeared to correlate with lower-velocity movement when drifting and stationary ice had locked up. The more sustained harmonic in January 2022 mirrored larger-mass impacts and the transfer of more ice-to-ice momentum.

“Radar images provide useful visuals, but we needed the seismic data to show what’s happening away from the surface, away from the camera lens,” Zhu said.

Merging seismic and radar data serves as a new research tool that can drive future studies to help protect coastal communities, the researchers said. Zhu estimated that Utqiaġvik residents live as close as 100 feet to the coast, leaving them especially vulnerable to erosion and waves created by drifting ice.

“In the context of a rapidly changing Arctic, this multi-sensor approach could help the communities better evaluate immediate hazards as Arctic ice continues to break apart and strike coastal areas, as the drifting ice can be tough to characterize otherwise,” Zhu said.

The new insights also can be useful for residents and those who make their livelihood in the area. Fishermen, for example, depend on sea ice as a fishing platform, so they need to know whether it’s stable, Dos Santos said.

“What we’ve found is very applicable in different regions — in Antarctica, in Greenland, in Russia,” Dos Santos said, explaining that the work would be replicable with similar use of radar images and readily available seismic sensors.

Zhu said that his team, along with other collaborators at Penn State, plan to explore 20 years of prior seismic readings and ice movements in the Arctic region to see how the integrated data assessment approach holds up against the 2022 evaluations in the paper.

The study received support from the U.S. National Science Foundation, the U.S. Department of Energy and UIC Science LLC. The authors also thanked several colleagues for field support that made the effort possible: Penn State graduate students Min Liew, Xiaohang Ji, Ziyi Wang, Matt Hallissey and Nolan Roth; Ming Xiao, professor of civil engineering at Penn State; Anne Jensen and Dmitry Nicolsky, faculty members at the University of Alaska Fairbanks; and Eileen Martin and Ahmad Tourei, a faculty member and a graduate student, respectively, at the Colorado School of Mines.

At Penn State, researchers are solving real problems that impact the health, safety and quality of life of people across the commonwealth, the nation and around the world. 

For decades, federal support for research has fueled innovation that makes our country safer, our industries more competitive and our economy stronger. Recent federal funding cuts threaten this progress. 

Learn more about the implications of federal funding cuts to our future at Research or Regress.  

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Journal

Geophysical Research Letters

DOI

10.1029/2025GL117458 

Method of Research

Computational simulation/modeling

Subject of Research

Not applicable

Article Title

Seismic Tremors From Sea-Landfast Ice Interactions Near Utqiaġvik, Alaska

 

The Southern Ocean’s low-salinity water locked away CO2 for decades, but...

An AWI study gives a potential explanation as to why the ocean around Antarctica is defying climate model projections and continuing to absorb CO2, despite the effects of climate change

Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research

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An iceberg in the Weddell Sea, Southern Ocean

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Credit: Alfred Wegener Institute / Mario Hopmmann

Climate models suggest that climate change could reduce the Southern Ocean’s ability to absorb carbon dioxide (CO2). However, observational data actually shows that this ability has seen no significant decline in recent decades. In a recent study, researchers from the Alfred Wegener Institute have discovered what may be causing this. Low-salinity water in the upper ocean has typically helped to trap carbon in the deep ocean, which in turn has slowed its release into the atmosphere – until now, that is, because climate change is increasingly altering the Southern Ocean and its function as a carbon sink. The study is published in the journal Nature Climate Change.

Oceans absorb around a quarter of all anthropogenic CO2 emissions released into the atmosphere. Of this total, the Southern Ocean alone stores roughly 40 per cent, making it a key region for containing global warming. The Southern Ocean’s important role comes about due to the ocean circulation in the region, whereby water masses upwell from deeper levels, are renewed and then return to the depths. This process releases natural CO2 from the deep ocean and absorbs and stores anthropogenic CO2 from the atmosphere. How well the Southern Ocean is able to absorb anthropogenic CO2 depends on how much natural CO2 comes to the surface from the deep ocean: the more natural CO2 that rises to the surface from the deeper levels, the less anthropogenic CO2 the Southern Ocean is able to absorb. This process is controlled by ocean circulation and the stratification of different water masses.

The water that upwells from the depths in the Southern Ocean is extremely old, having not been at the surface for hundreds or thousands of years. Over time, it has accumulated large amounts of CO2 which naturally return to the surface through the upwelling process. Model studies show that strengthening westerly winds, caused by climate change, will cause more and more of this CO2-rich deep water to rise to the surface. In the long term, this would reduce the Southern Ocean’s capacity to absorb human-made CO2. However, contrary to climate model projections, observational data from recent decades has shown no reduction in its capacity as a CO2 sink. A new study from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) now provides an explanation as to why, despite strengthening westerly winds, the Southern Ocean has continued to act as a CO2 sink in recent decades and therefore been able to slow down climate change.

“Deep water in the Southern Ocean is normally found below 200 metres,” says Dr. Léa Olivier, AWI oceanographer and lead author of the study. “It is salty, nutrient-rich and relatively warm compared to water nearer the surface.” The deep water contains a large amount of dissolved CO₂ that entered the deep ocean from the surface a long time ago. Near-surface water, on the other hand, is less salty, colder and contains less CO₂. As long as the density stratification between deep and surface water remains intact, CO₂ from the deeper layers cannot easily rise to the surface.

Cold, low-salinity water keeps carbon-rich water contained – however, climate change brings CO₂ dangerously close to the surface

“Previous studies suggested that global climate change would strengthen the westerly winds over the Southern Ocean, and with that, the overturning circulation too,” says Léa Olivier. “However, that would transport more carbon-rich water from the deep ocean to the surface, which would consequently reduce the Southern Ocean's ability to store CO₂.” Although strengthening winds have already been observed and attributed to human-made change in recent modelling and observational studies, there is no evidence pointing to the Southern Ocean absorbing less CO₂ – at least at this point.

Long-term observations by the AWI and other international research institutes suggest that climate change may be affecting the properties of surface and deep water masses. “In our study, we used a dataset comprising biogeochemical data from a large number of marine expeditions in the Southern Ocean between 1972 and 2021. We looked for long-term anomalies, as well as changes in both circulation patterns and the properties of water masses. In doing so, we only considered processes related to the exchange between the two water masses, namely circulation and mixing, and not biological processes, for example,” explains Léa Olivier. “We were able to determine that, since the 1990s, the two water masses have become more distinct from one another.” The Southern Ocean’s surface water salinity has reduced as a result of increased input of freshwater caused by precipitation and melting glaciers and sea ice. This “freshening” reinforces the density stratification between the two water masses, which in turn keeps the CO₂-rich deep water trapped in the lower layer and prevents it from breaking through the barrier between the two layers.

“Our study shows that this fresher surface water has temporarily offset the weakening of the carbon sink in the Southern Ocean, as model simulations predicted. However, this situation could reverse if the stratification were to weaken,” summarises Léa Olivier. There is a risk of this happening, as the strengthening westerly winds push the deep water ever closer to the surface. Since the 1990s, the upper boundary of the deep water mass has shifted roughly 40 metres closer to the surface, where CO₂-rich water is increasingly replacing the low-salinity winter surface water. As the transition layer between surface and deep water moves closer to the surface it becomes more susceptible to mixing, which could be primarily caused by the strengthening westerly winds. Such mixing would release the CO₂ that had accumulated beneath the surface water layer.

A recently published study suggests that this process may have already begun. The result would be that more CO₂-rich deep water could reach the surface, which would in turn reduce the Southern Ocean’s capacity to absorb anthropogenic CO₂ and therefore further drive climate change. “What surprised me most was that we actually found the answer to our question beneath the surface. “We need to look beyond just the ocean's surface, otherwise we run the risk of missing a key part of the story,” says Léa Olivier. “To confirm whether more CO₂ has been released from the deep ocean in recent years, we need additional data, particularly from the winter months, when the water masses tend to mix,” explains Prof. Alexander Haumann, co-author of the study. “In the coming years, the AWI is planning to carefully examine these exact processes as part of the international Antarctica InSync programme, and gain a better understanding of the effects of climate change on the Southern Ocean and potential interactions.“

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Journal

Nature Climate Change

DOI

10.1038/s41558-025-02446-3 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Southern Ocean freshening stalls deep ocean CO2 release in a changing climat

Article Publication Date

17-Oct-2025

 

New study finds large fluctuations in sea level occurred throughout the last ice age, a significant shift in understanding of past climate

Oregon State University

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CORVALLIS, Ore. — Large changes in global sea level, fueled by fluctuations in ice sheet growth and decay, occurred throughout the last ice age, rather than just toward the end of that period, a study publishing this week in the journal Science has found.

The findings represent a significant change in researchers’ understanding of how the Pleistocene – the geological period from about 2.6 million to 11,700 years ago and commonly known as the last ice age – developed, said Peter Clark, a paleoclimatologist at Oregon State University and the study’s lead author.

“This is a paradigm shift in our understanding of the history of the ice age,” said Clark, a university distinguished professor in OSU’s College of Earth, Ocean, and Atmospheric Sciences.

During the last ice age, Earth experienced cycles of dramatic shifts in global sea level caused by the formation and melting of large ice sheets over northern areas of North America and Eurasia. These changes are recorded in the shell remains of microscopic marine organisms called foraminifera, which are found in ocean sediment and collected by drilling cores, giving scientists an important record of past climate history.

When the first reconstruction of global sea level over the last ice age was published nearly 50 years ago, the science suggested there was a transition period about 1.25 million to 700,000 years ago, known as the middle Pleistocene transition, when the size of the ice sheets and the cycle of forming and melting changed.

“Before that transition, the glaciation cycles occurred about every 41,000 years, and after the transition, the cycles were every 100,000 years and were larger in amplitude,” said Clark. “All theories developed to explain this transition were focused on an increase in the size of the ice sheets through this transition. Every sea level reconstruction since that initial study produced the same storyline until now.”

Researchers had two leading hypotheses to explain why the transition occurred. One suggests that global cooling from decreasing carbon dioxide levels contributed to the cycle change and the other suggested that changes in how ice sheets move played a role.

In the new study, researchers reconstructed sea level changes for the past 4.5 million years. They found that many of the glaciation cycles during the early Pleistocene, when the cycles were 41,000 years in duration, were as large as the more recent cycles.

“Having those large ice sheets present throughout that time means that their formation and decay were likely influenced by internal feedbacks in the climate system, rather than external dynamics,” Clark said. “This finding challenges the conventional wisdom on the middle Pleistocene transition and forces us to develop new explanations.”

The research builds on previous work by Clark and colleagues to reconstruct global atmospheric temperatures and mean ocean temperatures, a project that began in 2017 to further understand past climate dynamics.

“Our ability to understand the past gives us a greater understanding of ice sheet-climate interactions and provides context for what we might experience in the future,” Clark said. “We have two big ice sheets today, in Antarctica and Greenland, and it’s important to think about how ice sheets like this can exist under a variety of conditions.”

Co-authors of the study are Steven W. Hostetler and Nicklas G. Pisias of Oregon State University; Jeremy D. Shakun of Boston College; Yair Rosenthal of Rutgers University; David Pollard of Pennsylvania State University; Peter Kohler of the Alfred-Wegener Institute of Germany; Patrick J. Bartlein of University of Oregon; Jonathan M. Gregory of University of Reading of the United Kingdom; Chenyu Zhu of the Chinese Academy of Sciences; Daniel P. Schrag of Harvard University; and Zhengyu Liu of Ohio State University.

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Journal

Science

DOI

10.1126/science.adv8389 

Article Title

Global mean sea level over the past 4.5 million years

Article Publication Date

16-Oct-2025