Rapid melting of Antarctic sea ice largely driven by ocean warming

University of Gothenburg

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Southern Elephant seal with a CTD-SRDL tag.

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Credit: Photo: Dan Costa (UCSC)

Sea ice around Antarctica expanded for several decades until a dramatic decline in 2015. The reasons behind this are revealed by research from the University of Gothenburg.

Antarctic sea ice plays a crucial role in the ecosystem and physical environment of Antarctica and the Southern Ocean. Since the ice reflects the sun's rays and blocks heat exchange between the ocean and the atmosphere, it is critical to our weather and climate. Therefore, we need to understand what affects its extent to improve future climate models and prediction.

While Arctic sea ice has been steadily declining since satellite measurements of sea ice began, Antarctic sea ice has exhibited a completely different behaviour. After expanding slowly for several decades, Antarctic sea ice declined rapidly in late 2015 and has since experienced large year-to-year fluctuations in extent. Research on this change, led by the University of Gothenburg, is now published in Nature Climate Change.

Protective layer

“There was a protective layer of cold water beneath the sea ice in Antarctica that prevented warmer deep water from rising and melting the ice from below. But during the winter of 2015, storms in the Southern Ocean were unusually strong, reducing the cold-water protective layer effect and resulting in the sustained sea ice loss around Antarctica,” says Theo Spira, former doctoral student in oceanography at the University of Gothenburg and first author to the study.

Water masses with large differences in salinity and/or temperature do not mix easily and settle in layers on top of each other. This is called stratification. The cold Winter Water layer that protects the sea ice becomes increasingly fresh as the ice grows from more sea ice melt, and this increases stratification in relation to the warm and salty water layer below.

Storms stirred things up

This natural protection contributed to long-term growth in Antarctic Sea ice until 2015. However, under the ice the Winter Water layer slowly got thinner as the deep water got warmer, weakening the ocean’s protective cool layer.

“With the help of almost two decades of observations, I can see that the Winter Water layer has thinned over large parts of the Southern Ocean, allowing the deep, warm water to approach the surface. The storms in 2015 stirred up the sea and warmer water mixed with the cold-water layer, the protection disappeared and the ice melted at record speed,” says Theo Spira.

Elephant seals help scientists

The Southern Ocean is a remote environment for research, far from inhabited areas. Theo Spira used autonomous marine robots to measure temperature and salinity in the ocean water but also enlisted the help of elephant seals living in the area. Sensors were attached to their bodies, which accompanied them on their long dives hundreds of metres down into the ocean. After 10 months, the sensor detaches from the elephant seal.

“This is valuable because elephant seals live within and at the edge of the sea ice in Antarctica and can provide data on the stratification of the water there. Winter Water acts as a gatekeeper for heat exchange between the deep ocean and the surface, and by quantifying its role, my research identifies processes that are missing or poorly represented in today's climate models,” says Theo Spira.

 

The Antarctic sea ice is getting thinner in recent years.

Credit

Theo Spira

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Journal

Nature Climate Change

DOI

10.1038/s41558-026-02601-4 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Wind-triggered Antarctic sea ice decline preconditioned by thinning Winter Water

Article Publication Date

18-Mar-2026

 

Beavers can convert stream corridors to persistent carbon sinks

Playing a significant role in Europe’s climate mitigation efforts, beavers are transforming suitable river corridors into long‑term carbon stores.

University of Birmingham

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Beavers could engineer riverbeds into promising carbon dioxide sinks, according to a new international study led by researchers at the University of Birmingham.

The new paper, published in Communications Earth & Environment today, has for the first time calculated the carbon dioxide (CO2) emitted and sequestered due to engineering work done by beavers in suitable wetland areas. The research was led by the University of Birmingham, Wageningen University, the University of Bern, and numerous international partners and the study was conducted in a stream corridor in northern Switzerland which has seen more than a decade of beaver activity.

The researchers’ findings demonstrate that these beaver-engineered wetlands can store carbon at rates up to ten times higher than similar systems without beaver activity. Over a 13‑year period, the wetland accumulated an estimated 1,194 tonnes of carbon, equivalent to 10.1 tonnes of CO2 per hectare per year.

Dr Joshua Larsen, from the University of Birmingham and lead senior author of the study, said: “Our findings show that beavers don’t just change landscapes: they fundamentally shift how CO2 moves through them. By slowing water, trapping sediments, and expanding wetlands, they turn streams into powerful carbon sinks. This first-of-its-kind study represents an important opportunity and breakthrough for future nature‑based climate solutions across Europe.”

Beavers are increasingly returning to rivers and other natural landscapes across Europe, following decades of collaborative conservation efforts. The team have found that beavers dramatically reshape how CO2 is stored, cycled, and retained in headwater stream systems, which are the small, upstream beginnings of rivers.

By building dams, beavers flood stream margins, create wetlands, alter groundwater pathways, and trap large amounts of organic and inorganic material, including CO2.

This study suggests that efforts to further rewild beaver populations in suitable wetland areas could have a major benefit, with large amounts of carbon able to be captured, stored, and prevented from re‑entering the atmosphere.

Beavers working as ecosystem engineers

The research team combined high‑resolution hydrological data, chemical analysis, sediment sampling, greenhouse gas (GHG) monitoring, and long‑term modelling to construct the most comprehensive carbon budget ever produced for a beaver landscape in Europe.

Due to the beaver activity within the area, the wetland acted as a net annual carbon sink of 98.3 ± 33.4 tonnes of carbon per year, driven primarily by the removal and retention of dissolved inorganic carbon through subsurface pathways.

However, the beaver-engineered system also showed clear seasonal patterns. During the summer, when water levels receded and exposed sediment surfaces increased, carbon dioxide (CO₂) emissions temporarily exceeded retention - making the system a short‑term carbon source.

Over full annual cycles, the beaver‑driven accumulation of sediments, vegetation, and deadwood resulted in substantial net carbon storage. Notably, methane (CH₄) emissions - which are often a major concern in wetland systems - were found to be negligible, making up less than 0.1% of the carbon budget.

Dr Lukas Hallberg from the University of Birmingham and corresponding author of the study, said: “Within just over a decade, the system we studied had already transformed into a long‑term carbon sink, far exceeding what we would expect from an unmanaged stream corridor. This highlights the enormous potential of beaver-led restorations and offers valuable insights into potential land‑use planning, rewilding strategies, and climate policy.”

Implications for future climate management

Over time, carbon is locked away as sediments accumulate and deadwood builds in beaver-built wetlands. Researchers found that this sediment contained up to 14 times more inorganic carbon and eight times more organic carbon than surrounding forest soils. Meanwhile, deadwood from forested areas growing along riverbanks, streams, or wetlands (known as riparian forests) accounted for nearly half of all long‑term stored carbon.

These stores could persist over decades, suggesting that beaver‑modified wetlands act as reliable, long‑duration carbon sinks – so as long as their dams stayed intact.

Dr Annegret Larsen, Assistant Professor in the Soil Geography and Landscape Group at Wageningen University, said: “Our research shows that beavers are powerful agents of carbon capture and adsorption. By reshaping waterways and creating rich wetland habitats, beavers physically change how carbon is stored across landscapes.”

When scaled across all floodplain areas suitable for beaver recolonisation in Switzerland, researchers estimate that beaver wetlands could offset 1.2–1.8% of the nation’s annual carbon emissions: delivering climate benefits without active human intervention or financial cost.

Led by the University of Birmingham, Wageningen University, the University of Bern, and numerous international partners, the study was conducted in a stream corridor in northern Switzerland which has had over a decade of beaver-activity within it.

As beaver populations continue to expand, further research into understanding their role in shaping future ecosystems, and future carbon budgets, will be crucial.

ENDS

Notes to Editor:

For media enquiries and more information please contact Holly Young, Press Office, University of Birmingham, tel: +44 (0)7815 607 157.

‘Beavers can convert stream corridors to persistent carbon sinks’ - Lukas Hallberg, Annegret Larsen, Joshua R. Larsen et al is published in Communications Earth & Environment

About the University of Birmingham

The University of Birmingham is ranked amongst the world’s top 100 institutions. Its work brings people from across the world to Birmingham, including researchers, educators and more than 40,000 students from over 150 countries.

England’s first civic university, the University of Birmingham is proud to be rooted in of one of the most dynamic and diverse cities in the country. A member of the Russell Group and a founding member of the Universitas 21 global network of research universities, the University of Birmingham has been changing the way the world works for more than a century.

About Wageningen University

The mission of Wageningen University & Research is “To explore the potential of nature to improve the quality of life”. Under the banner Wageningen University & Research, Wageningen University and the specialised research institutes of the Wageningen Research Foundation have joined forces in contributing to finding solutions to important questions in the domain of healthy food and living environment.

With its roughly 30 branches, 7,700 employees (7,000 fte), 2,500 PhD and EngD candidates, 13,100 students and over 150,000 participants to WUR’s Life Long Learning, Wageningen University & Research is one of the leading organisations in its domain. The unique Wageningen approach lies in its integrated approach to issues and the collaboration between different disciplines.

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Journal

Communications Earth & Environment

DOI

10.1038/s43247-026-03283-8. 

Method of Research

Commentary/editorial

Subject of Research

Animals

Article Title

Beavers can convert stream corridors to persistent carbon sinks

Article Publication Date

18-Mar-2026

 

How birds send heat into space measured for the first time: A new study reveals hidden reflectance of bird feathers through the prism of light, heat, and color

Scientists at the Natural History Museum of Los Angeles County, UCLA, Indiana University, and Cal State University, Dominguez Hills, flock together to measure the reflectance of mid-infrared in bird feathers for the first time.

Natural History Museum of Los Angeles County

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Population-level differences in (left) emittance coefficients and (right) MIR reflectance spectra in bobwhites. Bobwhites from Iowa and Florida, and Florida and Mexico, did not differ in their emittance coefficients, while bobwhites from Iowa had significantly higher emittance than those from Mexico, though comparisons are limited by the small sample size (n = 3 birds/population). The gray dashed line shows atmospheric transmission (%). ns = not significant; ***
390 = p < 0.001. 

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Credit: T Lee, M Barrett, L Pilon, A J Shultz, T McGlynn

As human-caused climate change continues to raise temperatures across the globe, understanding how birds regulate their temperature is vital for their conservation. But how much heat birds emit—an invisible spectrum of radiation known as mid-infrared—has never been studied, until now. Published in the journal Integrative Organismal Biology, a groundbreaking collaboration between material engineers and museum biologists explored the impact of mid-infrared on birds for the first time in history, reflecting the hidden prism of light, heat, and color in bird feathers.  

It’s long been known that habitat plays a role in bird coloration, a phenomenon described by biologists through things like Gloger’s rule, which predicts that animals like birds living in hot, humid areas will be visibly darker than those in dry, cool areas. Color is part of the electromagnetic spectrum, a visible wavelength that humans can see part of (the visible spectrum), and birds can see even more of (the ultraviolet spectrum), but heat, or infrared, exists outside the bounds of what either humans or birds can see. Infrared is broken down into the heat animals absorb (near-infrared) but not the heat they emit (mid-infrared). The interdisciplinary team of scientists measured both in the new study.

“A ‘hot’ topic in thermal engineering is to create passively cooling structures, and it’s no secret to engineers that nature contains some of the most optimized, multifunctional adaptations that we would want to replicate. In order to uncover what it is about animals that allows them to manage their thermal loads, collaborations like this one are required to share interdisciplinary knowledge with one another,” says co-lead author Thomas Lee, PhD Candidate at UCLA. Researchers from UCLA’s engineering department provided crucial technical expertise and advanced, specialized instruments like spectrometers that are typically beyond the reach of biologists. The study opens the door to further interdisciplinary research exploring bioinspired design along with birds’ ability to cope with rising temperatures.

“It's hard to get access, and also many engineers don't want dirty biological materials in their very fancy, expensive equipment,” says co-author Dr. Allison Shultz, Curator of Ornithology at the Natural History Museum of Los Angeles County.

The research team measured the mid-infrared and near-infrared reflectances, as well as the visual and ultraviolet spectrum (which birds can see) of five species of birds from three regions across North America: the great horned owl, Northern bobwhite, Stellar’s jay, song sparrow, and common raven. For each species, the team examined museum specimens from geographically diverse areas across North America, representing regional subspecies of the five birds. Out of the five, bobwhites showed the most variation in heat emittance, suggesting one big factor influencing mid-infrared radiation in birds is their exposure to the vacuum of space.

“Whenever you go outside, and you don't have a ceiling, a roof, or a tree over your head, because space is so cold compared to Earth, heat is being emitted into space,” says Shultz. Bobwhites typically prefer open prairies and grasslands, making mid-infrared more impactful on their survival. “If you live in the forest and you're never exposed, mid-infrared might not be a really big selective pressure. But if you're living out in the open, if you're a grassland bird, for example, you are exposed to the sky quite a lot of the time. So that might be a larger selective pressure for you.”

Comparing the birds’ absorptance of near-infrared radiation also revealed some surprises. “When we divided up the common ravens by subspecies,  they had significantly different and near-infrared absorptance profiles,” says Shultz. “These are birds that just look like they're the same black to us, but their feathers are taking in heat at different rates, so something else is going on.”

A better understanding of how color, light, and heat interact with bird feathers could lead to breakthroughs in developing new materials that conduct heat more efficiently, and the same understanding can help us predict how bird populations might cope with rising temperatures. This study is only the first step. “It’s exciting to learn that the feathers of birds are evolving to shed heat into outer space to track climatic challenges,” says co-author Dr. Terry McGlynn, Professor of Biology at Cal State University Dominguez Hills. “We are eager to find out how this works at the microscope scale in bird feathers.”  

 

The five bird species (from left to right: great-horned owl, common raven, Stellar's jay, bobwhite, and song sparrow showed remarkable similarity in mid-infrared radiation—except for bobwhites.

Credit

Allison Shultz

 

A nitrogen-purged Fourier transform infrared (FTIR) spectrometer (Nicolet TM iS50, Thermo Scientific Fischer, USA) equipped with an integrating sphere (Upward IntegratIRTM, PIKE Technologies, USA) measuring NIR and MIR in a bobwhite specimen.

Credit

Thomas Lee

 Of the five species studied, bobwhites showed the greatest variance in mid-infrared reflectance.

Credit

iNaturalist observation by Adam Jackson

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Journal

Integrative Organismal Biology

DOI

10.1093/iob/obag006 

Method of Research

Observational study

Subject of Research

Animals

Article Title

Population- and species-level variation in near- and mid-infrared radiation in birds: a preliminary analysis

Article Publication Date

18-Mar-2026