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. The findings came as a bit of a surprise. "It is the first time we have seen this level of seepage outside the Arctic that is not associated with features like oil or gas reservoirs or active tectonic margins," said Prof Adam Skarke from Mississippi State University, who led the study.
The scientists have observed streams of bubbles but they have not yet sampled the gas within them. However, they believe there is an abundance of circumstantial evidence pointing to methane.
Most of the seeping vents were located around 500m down, which is just the right temperature and pressure to create a sludgy confection of ice and gas called methane hydrate, or clathrate.
The scientists say that the warming of ocean temperatures might be causing these hydrates to send bubbles of gas drifting through the water column.
Prof. Skarke and his colleagues estimate that worldwide, there may be around 30,000 of the type of seeps they have discovered.
They acknowledge that this is a rough calculation but they believe that it could be significant.
While the vents may not be posing an immediate global warming threat, the sheer number means that our calculations on the potential sources of greenhouse gases may need revising. The scientists also found abundant life around many of these seeps, but not perhaps as we know it.
The creatures they describe are termed chemosynthetic, meaning they derive energy from chemical reactions and not from the Sun as do photosynthetic organisms.