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Heriot-Watt scientists have discovered giant underwater mud waves buried deep below the Atlantic Ocean, 400 kilometers off the coast of Guinea-Bissau in west Africa.

The massive underwater sediment waves, comprising mud and sand, were found about one kilometer below the seabed.

They formed in what was known as the Equatorial Atlantic Gateway: the seaway that formed when South America and Africa split apart, giving birth to the modern Atlantic Ocean.

Dr. Débora Duarte and Dr. Uisdean Nicholson, geologists from the School of Energy, Geoscience, Infrastructure and Society, discovered the waves.

They say their findings, in the journal Global and Planetary Change, suggest that the Atlantic Ocean formed millions of years earlier than previously thought, and possibly ushered in a period of climate change.

A waterfall below the ocean's surface

The researchers used seismic data and cores from wells drilled as part of the Deep Sea Drilling Project (DSDP) in 1975.

They found five layers of sediment that were used to reconstruct the tectonic processes that broke up the ancient continent of Gondwana in the Mesozoic Era when dinosaurs dominated Earth.

Dr. Nicholson said, "One layer was particularly striking: it included vast fields of sediment waves and 'contourite drifts'—mud mounds that form under strong bottom currents.

"Imagine one-kilometer-long waves, a few hundred meters 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.

"They formed because of dense, salty water cascading out of the newly formed gateway. Think of it like a giant waterfall that formed below the ocean surface.

"This happened because of the strong density contrast between the relatively fresh waters of the open Central Atlantic waters to the north and the extremely salty waters to the south. 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."

Continents shifted earlier than thought

The discovery puts a new date on the opening of the Equatorial Atlantic Gateway and its impact on climate regulation at the time.

Dr. Duarte said, "The consensus has been that the gateway opened between 113 and 83 million years ago. The sediment waves show that the opening started earlier, from around 117 million years ago.

"This was a really important time in Earth's history when the climate went through some major changes.

"Up until 117 million years ago, 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."

"And we think that this was likely because of the first connection through this gateway and the inundation of seawater into these emerging basins.

"As the gateway gradually opened, this initially reduced the efficiency of carbon burial, which would have had an important warming effect.

"And eventually, a full Atlantic circulation system emerged as the gateway grew deeper and wider, and the climate began a period of long-term cooling during the Late Cretaceous period."

"This shows that the gateway played a really important role in global climate change during the Mesozoic."

Dr. 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."