Slower spreading rates could lead to a reduction in greenhouse gas emissions from volcanoes. And so researchers want to know the finer points of this.

Scientists have in a new study analyzed the so-called ‘oceanic distribution’ over the past 19 million years. It leads to a surprising discovery. Because the analysis shows that the oceanic spreading is much slower these days. But why?

Oceanic Spread

Driven by plate tectonics, new oceanic crust is constantly forming along fissures thousands of miles long on the seafloor. In a sense, you could say that the Earth’s surface is growing here. But our planet is not getting bigger, because the growth is compensated by subduction taking place elsewhere. Hereby the old crust is pulled down. Warm material rises from the Earth’s mantle in the form of magma, which fills the space created in the crust. This magma then causes volcanism at the plate boundary, forming a new crust of solidified magma. Once at the surface, the crust cools and is pushed away from the fissure where more new crust can form. And this cycle we call oceanic dispersion.

Speed

The rate of oceanic dispersion determines many global processes, including sea level and the carbon cycle. When the oceanic dispersion accelerates, it can lead to more volcanism, which in turn releases more greenhouse gases. Slowing oceanic dispersion could actually lead to a reduction in greenhouse gas emissions from volcanoes. In short, deciphering the spreading rates helps map long-term changes in the atmosphere.

Study

In the new study, the team studied 18 different oceanic ridges where oceanic spreading occurs. Specifically, the researchers focused on ridges in the eastern Pacific Ocean. The researchers measured the age of the seafloor to calculate how much ocean crust each ridge has formed over the past 19 million years.

Slower

The results show that each spine evolved a little differently; some grew longer while others shrunk. But surprisingly, there was one common denominator: Oceanic spreading is much slower on almost all ridges these days. In fact, the researchers make the surprising discovery that average oceanic distribution has slowed down by as much as 40 percent over the past 19 million years.

Why?

The pressing question, of course, is why the oceanic spread is slowing down. However, this is not so easy to figure out, partly due to the slow and steady self-destruction of the seabed (in the aforementioned subduction zones). “We know more about the surfaces of some other planets than we do about our own seafloor,” said researcher Colleen Dalton. “One of the challenges is the lack of storage. The seabed is being destroyed, so we don’t have all the information.”

Subduction Zones

The researchers do have a theory. For example, they suspect that we should look for the answer in the subduction zones. For example, if the Andes grows on the western edge of the South American continent, the mountains press on the crust. “Think of it as increased friction between two colliding tectonic plates,” Dalton explains. “A slowdown in convergence there could eventually cause a slowdown in dispersal on nearby ridges.”

Combination

Dalton points out, however, that this extra friction need not be the sole cause of the slowdown. Larger scale processes, such as changes in mantle convection, can also play a role. “In all likelihood, it’s a combination of both,” she concludes.

So why slow down oceanic dispersion? For the time being, researchers still owe us the answer. In further research, Dalton hopes to uncover the mystery to collect absolute, localized scattering rates. This allows her to better determine the cause of the delay.