117-million-year-old deep-sea mud waves unlock Atlantic Ocean’s birth story

Also called sediment waves, these are big formations on the ocean floor mainly made of mud and tiny sediment particles.

These waves are up to a kilometer long and hundreds of meters high, located about one kilometer below the seabed.

Their existence tells a powerful story about the birth of the modern Atlantic Ocean.   

Tracing the past

These giant waves formed in what’s known as the Equatorial Atlantic Gateway – the seaway that emerged as South America and Africa tore apart.

The study utilized seismic data and core samples from wells drilled in 1975. This helped them identify five distinct layers of sediment.

These layers act like a geological record.

“One layer was particularly striking: it included vast fields of sediment waves and ‘contourite drifts’ – mud mounds that form under strong bottom currents,” Uisdean Nicholson said. 

“Imagine one-kilometre-long waves, a few hundred metres 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,” the author added. 

Equatorial Atlantic Gateway opened earlier

The giant underwater mud waves formed due to dense, salty water flowing out of the newly created seaway, similar to a massive underwater waterfall. 

This underwater “waterfall” was created by a dramatic density difference.

Large salt deposits existed to the south. When the seaway opened, fresher water from the Central Atlantic flowed in, resulting in a dense, salty current moving outwards, which sculpted these huge underwater waves.

“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,” he explained. 

This discovery suggests the Equatorial Atlantic Gateway opened earlier than previously thought, around 117 million years ago instead of the 113-83 million year range. 

Dr. Débora Duarte highlights this period as significant for major climate shifts in Earth’s history.

“Up until 117 million years ago, the Earth had been cooling for some time, with huge amounts of carbon being stored in the emerging basins, likely lakes, of the Equatorial Atlantic. But then the climate warmed significantly from 117 to 110 million years ago,” Duarte said. 

The initial opening of the gateway, the researchers believe, disrupted the burial of carbon in the emerging basins, leading to a warming effect. 

As the gateway widened, a full Atlantic circulation system developed, eventually contributing to a long-term cooling trend later in the Cretaceous period. 

Nicholson said, “Understanding how past ocean circulation influenced climate is crucial for predicting future changes. 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.”

The findings were published in the journal Global and Planetary Change.