Nature: Seismic signs of escaping methane under the sea

A changing Gulf Stream is warming deep waters along the eastern United States and destabilizing greenhouse gases trapped in sediments.

Sand is not the only thing on the move in the waters off the eastern United States — a shift in the Gulf Stream is melting methane hydrate in sediments that could release methane gas.
(Image: D. Harvey/Natl. Geographic/Getty Images)

Nature magazine covered the research of SMU marine geologist Matthew Hornbach, who led the study that has uncovered a powerful new way to use data from the geological record to discover non-anthropogenic climate changes underway.

The study suggests warmer temperatures are destabilizing up to 2.5 gigatonnes of methane hydrate along the continental slope of the eastern United States.

From the study, the authors write:
“Here, using seismic data combined with thermal models, we show that recent changes in intermediate-depth ocean temperature associated with the Gulf Stream are rapidly destabilizing methane hydrate along a broad swathe of the North American margin. The area of active hydrate destabilization covers at least 10,000 square kilometres of the United States eastern margin, and occurs in a region prone to kilometre-scale slope failures. Previous hypothetical studies, postulated that an increase of five degrees Celsius in intermediate-depth ocean temperatures could release enough methane to explain extreme global warming events like the Palaeocene–Eocene thermal maximum (PETM) and trigger widespread ocean acidification. Our analysis suggests that changes in Gulf Stream flow or temperature within the past 5,000 years or so are warming the western North Atlantic margin by up to eight degrees Celsius and are now triggering the destabilization of 2.5 gigatonnes of methane hydrate (about 0.2 per cent of that required to cause the PETM).”

Co-author on the study is SMU geophysics doctoral student Benjamin Phrampus.

Read the full article.

EXCERPT:

By Virginia Gewin
Nature

Somewhere off the eastern coast of North Carolina, a frozen mixture of water and methane gas tucked in seabed sediments is starting to break down. Researchers blame a shifting Gulf Stream — the swift Atlantic Ocean current that flows north from the Gulf of Mexico — which is now delivering warmer waters to areas that had previously only experienced colder temperatures.

“We know methane hydrates exist here and, if warming continues, it can potentially lead to less stable sediments in this region,” says Matthew Hornbach, a marine geologist at the Southern Methodist University in Dallas, Texas, who led the study that is published online today in Nature1. The results suggest that the warmer temperatures are destabilizing up to 2.5 gigatonnes of methane hydrate along the continental slope of the eastern United States. This region is prone to underwater landslides, which could release the methane, a powerful greenhouse gas.

Whether that methane would make it to the atmosphere and worsen global warming is unclear, but scientists think that it is unlikely. “We don’t need to worry about any huge blow of methane into the atmosphere,” says Carolyn Ruppel, a geophysicist at the US Geological Survey in Woods Hole, Massachusetts. Rather, she says, Hornbach and his co-author Benjamin Phrampus, also of the Southern Methodist University, have uncovered a powerful new way to use data from the geological record to catch non-anthropogenic climate changes that are already happening.

Read the full article.

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