The Mid-Atlantic Ridge near the equator is offset by huge faults, called fracture zones, that are thousands of kilometers wide and tens of kilometers deep. A strong deep current flows along and through these fracture zones, almost straight across the South Atlantic. The combination of currents and fracture zones may act as a physical barrier blocking the transport of vent fauna between the North and South Atlantic Oceans—a subsea equivalent of a Berlin Wall. (Illustration by E. Paul Oberlander, Woods Hole Oceanographic Institution)[back]
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