Clues from last ice age 'show how oceans may respond to global warming'

Rob Waugh
·Contributor
Mon, January 22, 2024 

Could the oceans make climate change even worse? (Getty Images)


Ancient deposits on the ocean floor could offer a clue as to how the seas will respond to global warming, scientists believe.

The deposits could also show whether oceans will release greenhouse gases from carbon stored within deep waters.

Researchers in the US analysed ocean oxygen level and its connections with carbon dioxide (CO2) in the Earth's atmosphere during the last ice age, which ended more than 11,000 years ago. They said their findings could offer an insight into how the oceans will respond as the world warms.


Oceans adjust atmospheric CO2 as ice ages transition to warmer climates by releasing carbon – and the researchers warned that carbon release from the deep sea may rise as the climate warms.

"The research reveals the important role of the Southern Ocean in controlling the global ocean oxygen reservoir and carbon storage," said Yi Wang, lead researcher and an assistant professor of earth and environmental sciences at Tulane University School of Science and Engineering in New Orleans. "This will have implications for understanding how the ocean, especially the Southern Ocean, will dynamically affect the atmospheric CO2 in the future."
How did they do it?

The team analysed sea floor sediments collected from the Arabian Sea to reconstruct average global ocean oxygen levels thousands of years ago. They precisely measured isotopes of the metal thallium trapped in the sediments, which indicate how much oxygen was dissolved in the global ocean at the time the sediments formed.

"Study of these metal isotopes on glacial-interglacial transitions has never been looked at before, and these measurements allowed us to essentially recreate the past," said Wang, who specialises in marine biogeochemistry and paleoceanography.

The thallium isotope ratios showed the global ocean lost oxygen overall during the last ice age compared to the current warmer interglacial period.

The study revealed a thousand-year global ocean deoxygenation during abrupt warming in the Northern Hemisphere. The ocean gained more oxygen when abrupt cooling occurred during the transition from the last ice age to today.
What could this mean for climate change?

The oceans release carbon during warmer periods, the researchers said, and it could mean that the Southern Ocean releases more carbon as the world warms.

The researchers attributed the observed ocean oxygen changes to Southern Ocean processes.

The Antarctic or Southern Ocean plays a large role, according to researchers. (Getty Images)

Sune Nielsen, associate scientist at Woods Hole Oceanographic Institution (WHOI) in Massachusetts and co-author of the research, said: "This study is the first to present an average picture of how the oxygen content of the global oceans evolved as Earth transitioned from the last glacial period into the warmer climate of the last 10,000 years.

"These new data are a really big deal because they show that the Southern Ocean plays a critical role in modulating atmospheric CO2. Given that high latitude regions are those most affected by anthropogenic climate change, it is troubling that these also have an outsize impact on atmospheric CO2 in the first place."
Recommended reading

MIT researchers have discovered a remarkable new way to clean up air pollution — by starting with our oceans

Brett Aresco
Mon, January 22, 2024


Carbon capture — commonly thought of as the use of technology to remove carbon dioxide from the air — is a hotly debated topic.

Though the U.S. Department of Energy committed $131 million to various carbon capture projects, opponents claim that focus on carbon capture distracts from other, more effective strategies for combating our warming planet.

Now, an MIT research team may have found a way to make everybody happy: by removing carbon dioxide from the world’s oceans.

In a paper published in the journal Energy & Environmental Science, six MIT engineers have detailed a comprehensive plan for cleansing seawater of carbon dioxide.

The process utilizes two asymmetrical electrochemical cells consisting of silver and bismuth electrodes. The first cell releases protons into the water that converts to carbon dioxide that is then collected by a vacuum. The second cell then returns the seawater to a more basic state before releasing it back into the ocean, free from carbon dioxide.

The researchers say the process has “a relatively low energy consumption” and “high electron efficiency.” It’s also expected to cost less than comparable air-based carbon capture technologies. After capture, the isolated carbon dioxide could be stored under the seafloor or used on land to make fuels, chemicals, or even products.

Removing carbon dioxide from the world’s oceans is more important than ever, as they absorb 50 times more carbon than the atmosphere and 20 times more than all the world’s plants and soil combined.

According to the International Atomic Energy Agency, 26% of the carbon dioxide produced by human activity is absorbed by the ocean, and high carbon dioxide concentration has caused widespread ocean acidification. The more acidic oceans become, the harder it is for coral and other species to build their shells and exoskeletons, leading to disrupted ecosystems and less marine life.

The researchers behind the new carbon capture technology note that carbon dioxide in seawater is more than 100 times more concentrated than it is in the air but that a focus on water-based carbon capture has been lacking.

“The total amount of CO2 emissions partitioning into the oceans rivals that retained by the atmosphere,” the researchers write, “and thus effective means for its removal could augment the other negative emissions technologies to reduce the environmental burden imposed by this greenhouse gas.”

The technology proposed by the new research, which is expected to be demonstration-ready in 2025, has the potential to change the face of carbon capture.

Currently, the nonprofit Food & Water Watch says the idea of carbon capture amounts to “pie-in-the-sky greenwashing technologies” that will “only prolong the fossil fuel industry.”

But the deployment of large-scale, energy-efficient, ocean-based carbon capture could turn be a powerful tool for creating a healthier planet.