Source of vast, mysterious underwater methane reservoir finally discovered

21 Aug 2019

The manipulator arm of the remotely operated vehicle, Jason, samples a stream of fluid from a hydrothermal vent. Image: Chris German/WHOI/NSF/ NASA/ROV Jason 2012/ WHOI

Researchers have been trying to pinpoint an enormous reservoir of methane located beneath the planet’s oceans, and now they have an origin story.

Scientists working for the Woods Hole Oceanographic Institution (WHOI) have published findings that reveal evidence for the formation of a massive reservoir of abiotic methane. Unlike typical sources of methane produced by organic matter, this methane is formed purely from chemical reactions.

For some time now, researchers have tracked large quantities of this type of methane being emitted from deep-sea vents but, until now, its source had remained a complete mystery. With this discovery, it indicates that it could also be found on planets and moons that are no longer home to liquid water.

This latest research showed that pockets of methane existed in 160 rock samples obtained from across the world’s oceans. Frieder Klein, lead author of the study, said the researchers were “totally surprised” to discover estimates that put the methane reservoir as being more than the amount in Earth’s atmosphere before industrialisation.

Analysing these rocks using Raman spectroscopy – a laser-based microscope that allows them to identify fluids and minerals in a thin slice of rock – the researchers found nearly every sample contained a number of minerals and gases. These form when seawater moving through the deep oceanic crust is trapped in magma-hot olivine. As the mineral cools, the water trapped inside undergoes a chemical reaction – a process called serpentinisation that forms hydrogen and methane.

This is an important discovery because in otherwise inhospitable environments, just two ingredients – water and olivine – can form methane.

“Identifying an abiotic source of deep-sea methane has been a problem that we’ve been wrestling with for many years,” said Jeffrey Seewald, one of the study’s authors.

“Here’s a source of chemical energy that’s being created by geology.”

The news comes after the confirmation of a super-deep reservoir of rock that produced a number of incredibly rare diamonds. This reservoir would be a look back in time at the early formation of our planet as it would be devoid of asteroid impacts and violent geological activity.

Colm Gorey was a senior journalist with Silicon Republic