Scientists have discovered giant mud waves buried deep below the Atlantic Ocean around 250 miles off the coast of Guinea-Bissau, a country in west Africa.
Made of mud and sand, these massive underwater sediment waves lie around 3,280 feet below the seabed, researchers reported in a new study.
They were formed in the “Equatorial Atlantic Gateway”— the seaway that resulted from South America and Africa splitting apart, which created the Atlantic Ocean.
The findings of the study, published in the journal Global and Planetary Change, suggest that the Atlantic Ocean may have formed millions of years earlier than previously thought, igniting a period of climate change.
Using seismic data and cores from wells drilled as part of the Deep Sea Drilling Project in 1975, the researchers found five layers of sediment that they used to reconstruct the tectonic processes that divided the ancient continent of Gondwana in the Mesozoic era, when dinosaurs dominated the Earth.
“This direct sedimentary evidence shows the establishment of a marine connection started at around 117 million years ago, significantly earlier than previous estimates, and coinciding with the onset of global climate cooling,” the researchers wrote.
“These findings show the dynamic interplay between gateway opening, ocean circulation and climate change during the middle Cretaceous [period], highlighting the pivotal role of ocean gateways in Earth’s climate system,” the researchers added.
One striking layer of sediment included vast fields of sediment waves and “contourite drifts,” which are mud mounds that form under strong bottom currents, noted Uisdean Nicholson, one of the two geologists from the School of Energy, Geoscience, Infrastructure and Society who discovered the waves.
“Imagine one-kilometer [around 3,280 feet]-long waves, a few hundred meters [around 328 feet] high—a whole field formed in one particular location to the west of the Guinea Plateau, just at the final ‘pinch-point’ of the separating continents of South America and Africa,” Nicholson said in a statement.
These waves were formed from the strong contrast in density between the fresh waters of the open Central Atlantic waters in the north and the salty waters in the south. The dense, salty water spilled out from the newly formed gateway, Nicholson said.
He added: “Think of it like a giant waterfall that formed below the ocean surface.”
The researcher explained: “Just before this time, huge salt deposits were laid down in the South Atlantic. When the gateway opened, fresh water poured into these narrow basins, and the denser, more saline water flowed out to the north, forming these giant waves.”
The study’s findings put a new date on the opening of the Equatorial Atlantic Gateway and its impact on climate regulation. The gateway was previously believed to have opened between 113 and 83 million years ago. However, the discovery of the sediment waves indicated that the opening began earlier: from around 117 million years ago.
Paper co-author and geologist Débora Duarte explained that up until 117 million years ago, the Earth had been cooling for a while, with vast amounts of carbon stored in most likely lakes and other emerging basins of the Equatorial Atlantic.
“But then the climate warmed significantly from 117 to 110 million years ago,” Duarte said in a statement. “And we think that this was likely because of the first connection through this gateway and the inundation of seawater into these emerging basins.”
The efficiency of carbon burial was initially reduced as the gateway opened, which would have had a warming effect. A full Atlantic circulation system was formed as the gateway grew deeper and wider, and the climate entered a period of long-term cooling during the Late Cretaceous era. “This shows that the gateway played a really important role in global climate change during the Mesozoic,” Duarte noted.
“Understanding how past ocean circulation influenced climate is crucial for predicting future changes,” Nicholson said, adding: “Today’s ocean currents play a key role in regulating global temperatures, and disruptions, such as those caused by melting ice caps, could have profound consequences.”
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Reference
Duarte, D., Erba, E., Bottini, C., Wagner, T., Aduomahor, B., Jones, T. D., & Nicholson, U. (2025). Early Cretaceous deep-water bedforms west of the Guinea Plateau revise the opening history of the Equatorial Atlantic Gateway. Global and Planetary Change, 249. https://doi.org/10.1016/j.gloplacha.2025.104777
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