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The Atlantic Ocean did not spring into existence in a sudden tectonic snap; its earliest pulse can now be traced through a set of one-kilometer-long mud waves lying more than 3,000 feet below today’s seafloor some 250 miles west of Guinea-Bissau.

New seismic profiles and cores date these colossal ripples to roughly 117 million years old, which shifts the birth certificate of the Equatorial Atlantic Gateway back by at least four million years and forces geologists to rethink how water first threaded between Africa and South America.

Dr. Uisdean Nicholson and Dr. Débora Duarte of Heriot-Watt University’s School of Energy, Geoscience, Infrastructure and Society pieced the story together after combing through decades-old Deep Sea Drilling Project logs and new high-resolution seismic lines.

Atlantic mud waves written in stone

Continental fragments had been drifting apart since the Late Jurassic, yet the last sliver between the landmasses, a submarine corridor south of the present-day Guinea Plateau, stayed welded shut.

Earlier reconstructions placed the full marine connection somewhere between 113 million and 83 million years ago; the new evidence reveals that salt-laden water began spilling northward as early as 11 million years ago, years before dinosaurs like Iguanodon faded from the record.

A sediment wave is a rhythmic ridge built by persistent bottom currents, and the ones mapped here stand several hundred yards high in neat, parallel rows that stretch for more than half a mile each.

Farther upslope sit bulbous contourite drifts, mounds of fine mud stacked by slower but equally steady flows that took over once the seaway widened and currents lost their punch.

“These are one-kilometre-long waves, a few hundred metres high,” said Dr. Nicholson, who compared their scale to the overland dunes of the Namib Desert.

Because each layer in the wave field contains shells and microfossils pinned to a precise time window, the team could bracket the first surge of dense outflow with unusual confidence.

Salty underground siphon

Before sea water entered, isolated basins south of the gateway had been evaporating under a tropical sun, concentrating brine until it became much denser than the fresher Central Atlantic water to the north.

When the tectonic sill finally cracked, the brine slipped downslope like a submarine cataract, scouring the seabed and sculpting the massive waves that now serve as a timestamp for the opening event.

“The sediment waves show that the opening started earlier, from around 117 million years ago,” said Dr. Duarte, underscoring that the outflow was strong enough to rework sediment yet focused enough to leave a coherent bedform train.

Laboratory models suggest such density-driven cascades can reach speeds exceeding three feet per second, enough to loft sand and carve yard-high relief even a mile beneath the surface.

Signals of a warming world

Carbon-rich mud had been settling undisturbed in the restricted basins, locking away greenhouse gases and helping the planet cool through the Early Cretaceous.

As seawater intruded, that carbon burial factory sputtered, and global temperatures climbed markedly between 117 million and 110 million years ago, an interval recorded in marine carbonate oxygen-isotope curves and linked in climate models to changing gateway geometry.

Once the channel deepened further, full two-way flow kicked in, overturning water masses across equatorial latitudes and setting the stage for the long, slow cooling phase that followed in the Late Cretaceous.

Ocean-seaway studies from entirely different eras show a recurring pattern: tweak a gateway and climate systems pivot, a relationship explored for younger passages such as the Miocene Mediterranean corridors.

Why 117 million years matters

Climate models often rely on boundary conditions tied to plate reconstructions; missing the start of deep-water exchange by even a few million years can skew simulated temperature gradients and biosphere feedbacks.

The new date tightens those constraints and helps explain why certain mid-Cretaceous warming spikes coincide with geochemical signs of reduced organic-carbon burial rather than volcanic outbursts alone.

Field data also offer a calibration point for salinity-driven overflow physics, which modern scientists use to anticipate future behavior of dense plumes coming off melting ice shelves.

By showing how a narrow slot once amplified flow power, the study highlights the risk that present-day straits, such as the Greenland-Iceland gap, could magnify changes in North Atlantic circulation if density contrasts intensify.

Atlantic Ocean waves and currents

Today’s Atlantic Meridional Overturning Circulation (AMOC) depends on a delicate balance of salt and temperature, and its slowdown is one of the major wild cards in climate projections.

Understanding past density-driven waterfalls helps researchers judge whether fresh water from ice melt will merely reroute currents or switch them off for centuries, as some paleoclimate analogs hint.

Coring campaigns now aim to tie the Equatorial Atlantic Gateway record to contemporaneous sections in Brazil and Angola, seeking complementary wave fields that would show how overflow evolved along the entire rift.

Isotope geochemistry teams are likewise re-examining mid-Cretaceous carbon-cycle models to quantify how much the early leakage altered atmospheric carbon dioxide.

Nicholson and Duarte plan to feed their seismic grids into high-resolution flow simulations that treat each wave crest as a flow sensor from deep time.

If the models can reproduce the observed bedform geometry, the same equations could sharpen forecasts for modern channels responding to anthropogenic change.

The study is published in Global and Planetary Change.

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