“…authigenic carbonates observed imply that emissions have continued for more than 1,000 years at some seeps.”
From the BBC – 24 August 2014 ‘Widespread methane leakage’ from ocean floor off US coast
Researchers say they have found more than 500 bubbling methane vents on the seafloor off the US east coast.
The unexpected discovery indicates there are large volumes of the gas contained in a type of sludgy ice called methane hydrate.
There are concerns that these new seeps could be making a hitherto unnoticed contribution to global warming.
The scientists say there could be about 30,000 of these hidden methane vents worldwide.
Previous surveys along the Atlantic seaboard have shown only three seep areas beyond the edge of the US continental shelf.
Here is the sonar image:
There are concerns that these new seeps could be making a hitherto unnoticed contribution to global warming……..
The scientists say that the warming of ocean temperatures might be causing these hydrates to send bubbles of gas drifting through the water column….
“But it is important to say we simply don’t have any evidence in this paper to suggest that any carbon coming from these seeps is entering the atmosphere.”
h/t to reader “Jimbo” in Tips and Notes
Widespread methane leakage from the sea floor on the northern US Atlantic margin
- Sharke et al. Nature Geoscience (2014) doi:10.1038/ngeo2232
Methane emissions from the sea floor affect methane inputs into the atmosphere1, ocean acidification and de-oxygenation2, 3, the distribution of chemosynthetic communities and energy resources. Global methane flux from seabed cold seeps has only been estimated for continental shelves4, at 8 to 65 Tg CH4 yr−1, yet other parts of marine continental margins are also emitting methane. The US Atlantic margin has not been considered an area of widespread seepage, with only three methane seeps recognized seaward of the shelf break. However, massive upper-slope seepage related to gas hydrate degradation has been predicted for the southern part of this margin5, even though this process has previously only been recognized in the Arctic2, 6, 7. Here we use multibeam water-column backscatter data that cover 94,000 km2 of sea floor to identify about 570 gas plumes at water depths between 50 and 1,700 m between Cape Hatteras and Georges Bank on the northern US Atlantic passive margin. About 440 seeps originate at water depths that bracket the updip limit for methane hydrate stability. Contemporary upper-slope seepage there may be triggered by ongoing warming of intermediate waters, but authigenic carbonates observed imply that emissions have continued for more than 1,000 years at some seeps. Extrapolating the upper-slope seep density on this margin to the global passive margin system, we suggest that tens of thousands of seeps could be discoverable.