Scientists at the Woods Hole Oceanographic Institution (WHOI) have observed the Earth’s crust forming in an entirely unexpected way — and one that could affect the world’s climate.
Molten magma is constantly welling up along undersea ridges at the boundaries of tectonic plates. The process is critical to the planet’s metabolism, including the cycle of underwater life and the balance of carbon in the ocean and atmosphere.
But at the Guaymas basin in the Gulf of California, this is taking place in an unusual way – injecting swaths of magma called sills as far as 50 kilometers away from the plate boundary, on each side of the ridge — nearly ten times farther from such an active ocean ridge than had been observed before.
“There is something different about this ridge,” says geologist S Adam Soule. “Somehow it allows the magma to keep spreading.”
Unlike conventional ocean crust production, where magma bubbles up through volcano-like openings in a narrow – five-kilometer-or-so – zone at the plate boundary, these magmatic sills never quite make it to the ocean floor, stopping instead in the thick layers of organic-rich sediment that fill the basin.
The process releases significant amounts of carbon from sediments. By raising the temperature of the surrounding sediments, the sills produce up to ten times more CO2 and methane gas than a similar volume of volcanic rocks spewed through a vent onto the seafloor.
The researchers aren’t sure just how much of these greenhouse gases remain in the sediment and the water, how much they affect the biological communities, and how much CO2 and methane escapes into the atmosphere.
Soule suspects the Gulf of California is far from the only place on the planet where this phenomenon is occurring. He says there are “lots of places”, including the Red Sea, with similar characteristics.
“Sills derived from intrusive volcanism in sedimentary basins have been linked to huge natural methane fluxes in the past,” writes David Goldberg of the Lamont Doherty Earth Observatory writes in Nature Geoscience.
“Further research concerning the biological uptake from seafloor vents is also needed. But what we know now is that sills such as those observed below the Gulf of California, which naturally vent fluids to the ocean, seem to be carbon sources as they cool.”