Methane gas is escaping from the seabed sediments somewhere off the coast of North Carolina. Researchers think that a shifting Gulf Stream, the Atlantic Ocean current that flows north from the Gulf of Mexico, is to blame since it is delivering warmer waters to areas that had previously only received colder waters.
The scientists published their findings in the journal Nature. The methane hydrates could lead to less stable sediments in the region if the warming continues, states Matthew Hornbach, a marine geologist at the Southern Methodist University in Dallas, Texas, and lead author of the study. These warmer temperatures could destabilize up to 2.5 gigatonnes of methane hydrate along the continental slope of the eastern USA. This region is already prone to underwater landslides, which could release the methane.
It’s still unclear whether the methane would make it into the atmosphere and possibly worsen global warming, but scientists think that this is an unlikely event. This study has uncovered a powerful new way to use data from the geological record to catch non-anthropogenic climate changes that are already happening, states Carolyn Ruppel, a geophysicist at the US Geological Survey in Woods Hole, Massachusetts.
The scientists combined models of subsurface temperature dynamics with seismic images to directly detect the depth at which the methane hydrate is no longer stable and shifts from a frozen solid to free gas. The hydrate’s formation is dependent on temperature and the position of the bottom of this frozen zone can be used to estimate subsurface temperature dynamics.
The observed interaction between the frozen solid and the free gas was much deeper than previously expected. The team ruled out factors that could have explained these observations, like sea-level changes, increased sedimentation rates or decreased heat flow through sediments. The only thing that could cause this discrepancy was the water was cooler than in the past.
The heat flow was modeled through the methane hydrate sediments in relation to time, and it was estimated that it would take around 5,000 years of warmer water for all of the methane to sublimate and become gaseous. The scientists don’t know where we stand in relation to the 5,000-year time frame, but the best approximation suggests that we are 800 to 1,000 years in, states Benjamin Phrampus, Southern Methodist University, and co-author.
This study will help spur on more research into whether destabilized hydrates could make the continental slopes more unstable. Dramatic degassing events require changes in pressure. The Arctic is currently undergoing rapid warming and the dramatic loss of sea ice could be where the most dramatic oceanographic changes occur.