Was water in the deep Red Sea more vigorously circulating earlier in the Plio-Pleistocene?

What is it about?

The deep Red Sea today is hot and saline, and mostly quiescent. Consequently, modern sediments (desert dust and the shells of plankton) mostly drape the sediments that were deposited previously, like snow in wind-less conditions. But was the deep Red Sea quiescent millions of years ago? Seismic reflection data have reveal mounds formed on the seabed, formed by currents. Those currents were formed by water in the Gulf of Suez and other shallow areas being made dense by evaporation (which concentrates their dissolved salt) (Figure 1). Or, as the sea was much shallower at that time, eddies in the water surface, which are created today by winds crossing the Red Sea, were able to move sediment particles deeper in the sea, creating these mounds. The sediments overlie thick Miocene rock salt deposits. Rock salt is highly mobile, so the sedimentary layers above have been distorted (think of adding bags of sand onto a water bed). We compensated for that by vertically adjusting individual seismic traces ("flattening") to a prominent reflection that occurs on the top of the salt ("S"). The result revealed a number of low-relief mounds or dipping mounds, such as one off the coast of Egypt in Figure 2. Other mounds were found off the coasts of Saudi Arabia and Sudan.

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Photo by NEOM on Unsplash

Photo by NEOM on Unsplash

Why is it important?

The climate of East Africa is important for understanding the conditions under which early humans evolved. Hominin fossils as old as 1.8 m.y. have been found in a cave in Dmanisi, Georgia, so we might wish to know how the Red Sea obstructed their migrations into Asia. Various evidence, including the rapid water circulation, suggests that the Red Sea at Bab el Mandeb was a more formidible obstruction then, so hominins most likely migrated through Sinai as others have suggested. Signatures of the saline waters leaving the Red Sea can be found in the intermediate waters of the Indian Ocean. This too was likely different earlier in the Plio-Pleistocene, though exactly how different will depend on which of our scenarios best explains the sediment mounds and other factors.

Perspectives