More than 500 bubbling methane vents have been discovered on the seafloor off the U.S. east coast, according to BBC News.

The discovery indicates there are large volumes of the gas contained in a type of sludgy ice called methane hydrate. There is a concern that these new seeps could be making a hitherto unnoticed contribution to global warming.

Scientists believe there could be around 30,000 of these methane vents all over the world.

Previous studies along the Atlantic seaboard showed only three areas beyond the edge of the U.S. continental shelf, according to BBC News.

The team behind the discovery studied what is called the continental margin, or the location of the ocean floor that stands between the coast and the deep ocean.

In the area between Massachusetts and North Carolina they discovered 570 seeps at varying depths between 50m and 1,700m, according to BBC News.

The finding obviously came as a big surprise to the researchers.

"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, according to BBC News.

The researchers have observed streams of bubbles but they haven't sampled the gas within them yet.

They do believe however that there is an abundance of circumstantial evidence pointing to methane.

Most of the seeping vents were found around 500m down, which is the right temperature and pressure to create sludgy confection of ice and gas called methane hydrate, or clathrate, according to BBC News.

The scientists believe that the warming of ocean temperatures might be causing these hydrates to send bubbles of gas drifting through the water column. They don't seem to be reaching the surface however.

"The methane is dissolving into the ocean at depths of hundreds of metres and being oxidised to CO2," said Prof Skarke, according to BBC News. "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."

Estimates suggest that these undersea sediments are one of the largest reservoirs on Earth, and likely contains around 10 times more carbon than the atmosphere.

There could be around 30,000 of these type of seeps they discovered worldwide, according to Skarke, though this is just a rough calculation.

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