Unearthing the ‘Great Cut’ – Mississippi mud reveals the secrets of the ancient expansion of Antarctica

Colorful sunset in Antarctica

Mud cores from Mississippi have revealed clues about the formation of major ice sheets in Antarctica and an important cooling event, the Grand Coupeur. The research indicates that falling sea levels exposed organic carbon in coastal sediments, delaying the cooling of the climate by 300,000 years, as this carbon was released in the form of carbon dioxide into the atmosphere.

Evidence relating to the development of massive ice sheets in Antarctica has been revealed in mud samples taken from Mississippi, highlighting a major climate cooling event often referred to as Grand Coupeur or “great cut”.

A recent study in Nature CommunicationsResearchers from the University of Birmingham examined material from excavated cores near Jackson, Mississippi, USA.

The material in the core layers indicates that there has been a significant transfer of carbon from plant debris in coastal environments to the atmosphere, driven by a drop in sea level of about 40 meters with the formation of the Antarctic ice caps.

Whereas the initial formation of those ice caps, and the onset of the cooler modern climate over the past 34 million years, was due to long-term burial, or sequestration of carbon in sediments; The team found that falling sea levels halted the cooling of the climate for 300,000 years.

Rising seas expose coastal areas and their soft sediments to severe erosion by rain and rivers. The organic carbon, such as plant matter, that was once associated with these sediments and environments – think of today’s tropical mangrove swamps – was then exposed to oxygen in the air and made available for bacteria to feed on and convert back into carbon dioxide that can be extracted. released to the atmosphere.

Dr Tom Dunkley Jones of University of Birmingham He is the lead author of the paper and said:

“We’ve unearthed information from Mississippi mud to answer a key question about how the Antarctic ice expanded so dramatically to the continental scale.

“The Eocene-Oligocene transition is probably the largest climate cooling event on the planet and has had a major impact on Earth’s history. As sea levels fell during this transition, we can observe how a temporary suppression of atmospheric cooling occurred with the release of large amounts of carbon dioxide Carbon sequestration in coastal regions around the Mississippi River Basin.

“This solves a puzzle about the transition timeline and suggests that the beginnings of this event and the accumulation of the Antarctic ice sheets began around 300,000 years ago. Once the organic carbon brakes were applied, the transition was freed to continue its transition to the cooler state it has been in for the last 34 million years. past.

The research team studied samples of marine mud covering a depth of about 137 metres, and compared them to other major records of this event, particularly from the central Pacific Ocean. The team was able to use the data from the new samples to fill in gaps in the geological record, show how sediments deposited in the area have changed over time, and provide more accurate timings for the sea level drop that indicates the formation of ice sheets. .

Dr Kirsty Edgar, from the University of Birmingham, said:

“Our paper gives us valuable new insight into how Earth’s climate can undergo dramatic shifts and how this is often strongly linked to the biosphere and the carbon cycle.

“Understanding these past events gives us a clearer picture of the beauty and complexity of Earth’s climate and environment.”

Reference: “Multiple anecdotal evidence for sea-level drop at the beginning of the Eocene-to-Oligocene transition” by Marcelo A. De Lira Motta, Tom Dunkley-Jones, Norsovia Solomon, Kirsty M. Edgar, Tatsuhiko Yamaguchi, Melanie J. Laing, Marcus Adloff, Sarah E. Green, Richard Norris, Bridget Warren, Grace Duffy, Jennifer Farrant, Masafumi Murayama, Jonathan Hall and James Bindel August 8, 2023, Available here. Nature Communications.
doi: 10.1038/s41467-023-39806-6

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