Ancient rocks reveal themselves as ‘carbon sponges’

University of Southampton

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Cores of lava breccia, cemented with white calcium carbonate minerals, recovered from IODP Site U1557

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Credit: IODP JRSO

Sixty-million-year-old rock samples from deep under the ocean have revealed how huge amounts of carbon dioxide are stored for millennia in piles of lava rubble that accumulate on the seafloor.

Scientists have analysed lavas drilled from deep under the South Atlantic Ocean to understand how much CO2 is captured within the rocks due to reactions between the rocks and ocean.

The research, led by the University of Southampton, found that piles of lava rubble, formed due to erosion of seafloor mountains, form geological sponges for CO2.

It’s the first time the role of lava rubble as carbon sponges has been fully appreciated, and the research reveals secrets about Earth’s long-term carbon cycle.

Lead author of the research Dr Rosalind Coggon, Royal Society Research Fellow at the University of Southampton, said: “We’ve known for a long time that erosion on the slopes of underwater mountains produces large volumes of volcanic rubble, known as breccia – much like scree slopes on continental mountains.

“However, our drilling efforts recovered the first cores of this material after it has spent tens of millions of years being rafted across the seafloor as Earth’s tectonic plates spread apart.

“Excitingly, the cores revealed that these porous, permeable deposits have the capacity to store large volumes of seawater CO2 as they are gradually cemented by calcium carbonate minerals that form from seawater as it flows through them.”

Understanding past changes in the long-term carbon cycle

The movement of carbon between Earth’s interior, oceans, and atmosphere over millions of years controls how much CO₂ is in the air, which affects Earth’s climate.

To understand past climate changes, scientists study how much carbon moves in and out of different parts of the Earth system.

Dr Coggon explained: “The oceans are paved with volcanic rocks that form at mid-ocean ridges, as the tectonic plates move apart creating new ocean crust. This volcanic activity releases CO₂ from deep inside the Earth into the ocean and atmosphere.  

“However, ocean basins are not just a container for seawater. Seawater flows through the cracks in the cooling lavas for millions of years and reacts with the rocks, transferring elements between the ocean and rock. This process removes CO₂ from the water and stores it in minerals like calcium carbonate in the rock.”

The study determined how much CO2 is stored in the ocean crust, due to this process.

“While drilling deep into the seafloor of the South Atlantic, we discovered lava rubble that contained between two and 40 times more CO2 than previously sampled lavas,” said Dr Coggon.

“This study revealed the importance of such breccia, which forms due to the erosion of seafloor mountains along mid-ocean ridges, as a sponge for carbon in the long-term carbon cycle.”

The research was part of Expedition 390/393 of the International Ocean Discovery Program.

ENDS

Research vessel Joides Resolution

Credit

Dr Rosalind Coggon

Dr Rosalind Coggon examining cores of upper ocean crust lavas cored during IODP Expedition 390

Credit

Alyssa Stephens, IODP JRSO

Journal

Nature Geoscience

DOI

10.1038/s41561-025-01839-5 

Article Title

A geological carbon cycle sink hosted by ocean crust talus breccias

Article Publication Date

24-Nov-2025

 

Antarctic mountains could boost ocean carbon absorption as ice sheets thin

Research led by polar scientists from Northumbria University has revealed new hope in natural environmental systems found in East Antarctica which could help mitigate the overall rise of carbon dioxide in the atmosphere over long timescales.

Northumbria University

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Glaciers transport sediments from Antarctica to the coast. Credit: Dr Kate Winter, drone footage

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Credit: Credit: Dr Kate Winter, drone footage

Research led by polar scientists from Northumbria University has revealed new hope in natural environmental systems found in East Antarctica which could help mitigate the overall rise of carbon dioxide in the atmosphere over long timescales.

As Antarctica's ice sheets thin due to climate change, newly exposed mountain peaks could significantly increase the supply of vital nutrients to the Southern Ocean which surrounds the continent, potentially enhancing its ability to absorb atmospheric carbon dioxide, according to the research published in Nature Communications.

A team of scientists with expertise in oceanography, ice sheet modelling and geochemistry contributed to the study which looked at analysis of sediment samples from East Antarctica's Sør Rondane Mountains. They discovered that weathered rocks exposed above the ice surface contain iron concentrations up to ten times higher than previously reported from the Antarctic continent. This bioavailable iron is transported to the ocean by glaciers and icebergs, where it fuels the growth of phytoplankton – microscopic marine organisms that absorb CO₂ through photosynthesis.

The study found that sediments from mountain peaks protruding through the ice – known as nunataks – had over three times more extractable iron compared to sediments already being transported by glaciers. Some visibly rust-stained rock samples showed particularly elevated iron levels, suggesting that weathering processes on exposed surfaces create especially nutrient-rich material.

"Our results show that exposed bedrock in Antarctica acts like an iron factory," explained Dr Kate Winter, Associate Professor in the School of Geography and Natural Sciences at Northumbria University and lead author of the research paper. "Even though air temperatures rarely rise above freezing, sunlight can heat dark rock surfaces above 20°C in summer, creating the conditions needed for weathering and the formation of bioavailable iron compounds."

Dr Winter has travelled to Antarctica on fieldwork several times in recent years and has been supported by a Baillet Latour Antarctica Fellowship – a joint initiative of the Baillet Latour Fund and the International Polar Foundation (IPF). It provides scientists with the opportunity to conduct original research in East Antarctica’s cutting-edge Princess Elisabeth Antarctica research station.

Satellite observations confirm that coastal waters near to glacier outlets in the study region experience recurring phytoplankton blooms, demonstrating the biological importance of this natural iron delivery system. The blooms contribute to the Southern Ocean's role as a major carbon sink, absorbing atmospheric CO₂.

Dr Winter added: “The exciting thing is that we can take some hope from these findings because we know that carbon dioxide is a really important factor in climate change. From our research we now know that sediments from the Antarctic continent could help to draw down atmospheric carbon dioxide into the ocean. Whilst our study area is limited to one glacier system, what we need to understand is the potential impact of these many small amounts being drawn down together across the whole of Antarctica. Piecing together information to gather an accurate picture of how much these natural systems are working to reduce the amount of carbon in the atmosphere is crucial.”

However the research team, which includes scientists from the universities of Newcastle, Swansea, Plymouth, Edinburgh and Leeds, caution that there is a significant time lag in this process. Using ice flow models, they calculated that it takes between 10,000 and 100,000 years for iron-rich sediments collected in the mountains to reach the coast via glacial transport.

Dr Sian Henley, a marine scientist from the School of GeoSciences at the University of Edinburgh explained: “While the sediments we examine in the mountains today will take a long time to reach the ocean, we know from seafloor surveys that iron-rich sediments have been delivered to the coast for millennia, so the processes we record today give us a glimpse into changes we might expect to see in the future, as glaciers thin and more mountain surfaces are exposed in Antarctica.”

The study suggests that as temperatures continue to rise, several factors will increase iron delivery to the Southern Ocean:

• More mountain peaks will emerge as ice sheets thin
• Increased rock slope failures will deliver more sediment to glaciers
• Enhanced weathering will produce more bioavailable iron compounds
• Icebergs carrying this iron-rich sediment will distribute nutrients across vast ocean areas

The research provides important insights into how Antarctica's extreme environment connects with ocean ecosystems and the global carbon cycle. It also offers a glimpse into how this system may evolve as climate change continues to reshape the continent.

Discover more about research at Northumbria University which examines the future of ice on Earth.

FURTHER INFORMATION:

Visit the Northumbria University Research Portal to find out more about Dr Kate Winter’s work.

Thinning Antarctic glaciers expose high-altitude nunataks delivering more bioavailable iron to the Southern Ocean was published in Nature Communications on Monday 24 November 2025.

 

DOI: 10.1038/s41467-025-65714-y

 

Ends

Dr Kate Winter collecting glacial sediments in Dronning Maud Land. Credit: Jacque Richon, IPF

Credit

Credit: Jacque Richon, IPF

The Princess Elisabeth Antarctic Research Station is conveniently situated next to coastal margin mountains in East Antarctica. Credit: Dr Kate Winter, drone footage

Credit

Credit: Dr Kate Winter, drone footage

Dr Kate Winter in East Antarctica. Credit: Jacque Richon, IPF

Credit

Credit: Jacque Richon, IPF

During her fieldwork, Dr Kate Winter worked alongside renowned polar explorer Alain Hubert, who founded the International Polar Foundation. Credit: Henri Robert, IPF

Credit

Credit: Henri Robert, IPF

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Journal

Nature Communications

DOI

10.1038/s41467-025-65714-y 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

Thinning Antarctic glaciers expose high-altitude nunataks delivering more bioavailable iron to the Southern Ocean

Article Publication Date

24-Nov-2025

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"At the Mountains of Madness" by H. P. Lovecraft

Aug 20, 2009 ... At the Mountains of Madness By H. P. Lovecraft. I. I am forced into speech because men of science have refused to follow my advice without ...

 

Volcanic bubbles help foretell the fate of coral in more acidic seas

By 2100 Australian and global coral reef communities will be slow to recover, less complex, and dominated by fleshy algae, as high carbon dioxide changes ocean chemistry

Australian Institute of Marine Science

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A research vessel over volcanic seeps in PNG

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Credit: © AIMS | Katharina Fabricius

An international study published today in Communications Biology has used unique coral reefs in Papua New Guinea to determine the likely impact of ocean acidification on coral reefs in the face of climate change.

Oceans are becoming more acidic as they absorb carbon dioxide from the atmosphere, and that acid will dissolve coral limestone. But it’s hard to predict what impact this will have on whole ecosystems from studies using aquariums and models.

The research team, led by the Australian Institute of Marine Science (AIMS), studied entire coral reefs, locally enriched with CO2 that is seeping from the sea floor, near some of Papua New Guinea’s remote shallow submarine volcanoes.

Dr. Katharina Fabricius, a coral researcher at AIMS in Townsville and senior author on the paper, says the research has revealed which species can thrive under lifelong exposure to elevated CO2.

“These unique natural laboratories are like a time machine,” said Dr Fabricius.  

“The CO2 seeps have allowed us to study the reefs’ tolerance limits and make predictions. How will coral reefs cope if emissions are in line with the Paris Agreement level emissions? How will they respond to higher CO2 emissions scenarios?”

In 2000 Dr Fabricius came across bubbles of gas emerging through coral reefs while surveying species in Milne Bay, about 500 km east of Port Moresby. In 2009, as ocean acidification emerged as an issue, she thought back to that experience, had samples of the gas analysed and discovered it was nearly pure CO2.

The scene was set for the creation of a unique living laboratory and a decade-long research program to study how tropical marine ecosystems may adapt and how organisms acclimatise after generations of exposure to high CO2. 

Dr Sam Noonan, also from AIMS and first author on the paper, said: “These Papua New Guinea reefs are telling us that with every bit of increase in CO2, we will see fewer corals and more fleshy algae. Importantly, we also found far fewer baby corals, which means reefs won’t be able to grow and recover quickly. That has implications for all the species that depend on them, including humans. Many coastal communities depend on fish that start their lives using coral reefs for shelter and food.”

Oceans are slightly alkaline with a pH of 8.0, but their acidity has already increased by 30%. As CO2 emissions rise, the ocean pH is predicted to decline further down to a pH of 7.8 by the year 2100.

“By studying organisms at 37 sites along a 500-metre gradient of CO2 exposure, we were able to see what happens as CO2 increases. There was no sudden collapse or tipping point, instead, as the CO2 increased, we saw fleshy algae became dominant, replacing and smothering coral and calciferous algae,” Dr Fabricius said.

The reefs are hard to reach, requiring a flight into Papua New Guinea, a second to Milne Bay Province, then six hours in a boat.

“The coral reefs in Milne Bay are amazing, and the local people so welcoming. It was a real privilege to work at their reefs with these volcanic CO2 seeps, which are globally unique,” Dr Fabricius continued.

“Ocean acidification is a massive global problem, which has been understudied and underreported to date. This research is a first of its kind, presenting unique field data and allowing us to assess how whole communities change in the real world.

“We have observed coral reefs starting to change in response to CO2 gradients in the Great Barrier Reef. The Papua New Guinea reefs tell us what will happen next.

“The more CO2 we emit into the atmosphere, the greater the changes will be to coral reefs and the coastal communities which depend on them. This is on top of the impact of global warming and sea level rise.”

The research was conducted with colleagues from The University of Western Australia and Saudi Arabia.

Only bolder corals are found in areas of severe ocean acidification, (pH < 7.7, as predicted when atmospheric CO2 concentrations reach 1000 ppm). Coral reefs cease to exist at such conditions.

Credit

© AIMS | Katharina Fabricius

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Journal

Communications Biology

DOI

10.1038/s42003-025-08889-w 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Progressive changes in coral reef communities with increasing ocean acidification

Article Publication Date

24-Nov-2025