The oceans are not as equal as you may think. Scientists estimate that the Atlantic Ocean even widens by several inches every year. At the same time, the Pacific is shrinking.
This glacially slow shift of oceans is due to the continuous movement of the Earth’s tectonic plates as the plates under the Americas are separating from those underneath Europe and Africa.
The deep, geophysical forces underlying this epic phenomenon are far from fully understood, but researchers may have just made a significant contribution to what’s happening.
In a new study, scientists suggest that mid-ocean ridges – mountainous formations that form along the seafloor between tectonic plates – may be more involved in the transfer of material between the upper and lower mantle beneath the Earth’s crust than we previously thought.
The 39 seismometer locations. (University of Southampton)
“Sinking plates and rising plumes are widely accepted as sites of transmission, while mid-ocean ridges typically do not play a role,” a team led by seismologist Matthew Agius from the University of Southampton in the UK explains in a new paper.
“However, tight restrictions of it in situ ledge measurements have proven challenging. “
To fill the gaps in our knowledge, the researchers deployed a fleet of 39 seismometers along the bottom of the Atlantic Ocean to record seismic motion beneath the Mid-Atlantic Ridge – the marginal boundary that tectonically separates America from Europe and Africa.
Seismic measurements included in the experiment monitored material flow in the mantle transition zone that lies between the upper mantle and the lower mantle, allowing the team to image material transfer at depths as high as 660 kilometers (410 miles) below the surface.
The results suggest that upwelling of chemical material is not limited to shallow depths in the Mid-Atlantic Ridge, but may appear in the deepest reaches of the mantle transition zone, suggesting that material is rising up from the lower mantle.
“The observations imply material transfer from the lower to the upper mantle – continuous or intermittent – that is linked to the Mid-Atlantic Ridge,” the researchers explain.
“Given the length and lifespan of the mid-ocean ridge system, this implies that whole mantle convection is more common than previously thought.”
Deploy one of the seismometers. (University of Southampton)
While it was already known that mid-ocean ridges contributed to the phenomenon of seafloor spreading, the new findings show that the total processes involved extend much deeper into the Earth than previously measured, and can still occur in parts of the seafloor those not characterized by overt areas of plate subduction.
“[The work] refutes long-held assumptions that mid-ocean ridges could play a passive role in plate tectonics, ‘said senior researcher and geophysicist Mike Kendall of the University of Oxford.
“It suggests that in places like the Mid-Atlantic Ocean, ridge forces play an important role in driving newly formed plates apart.”
The findings are reported in Nature.