People walk along Santa Monica Beach. (File photo)
People walk along Santa Monica Beach. (File photo)

DOWNTOWN — How is Santa Monica’s popular ocean similar to a stockyard full of cattle?

Weekend visitors to the city by the sea found out on Sunday when a large, smelly release of methane gas erupted from the ocean floor, causing many to hold their noses as they reached for their cell phones to alert the local fire department.

The Santa Monica Fire Department responded to concerns with a public Facebook post, explaining that the event was natural, if unpleasant.

“This methane is not toxic, and dissipates quickly,” the post concluded.

The South Coast Air Quality Management District sent out an investigator, although the agency did not receive any complaints directly.

“We look for potential industrial sources such as an oil refinery, or gas distribution plant, but didn’t find anything,” said Sam Atwood, spokesperson for the AQMD.

Although no one has looked into the Sunday event too deeply, there are some theories, said Dana Roeber Murray, marine and coastal scientist with local nonprofit Heal the Bay.

The gas could have come from organic material like dead creatures and plants decaying on the ocean floor. If enough material accumulated there, the gas could have enough pressure to force it through to the surface, Murray said.

Another option could be underwater oil reservoirs.

“It doesn’t always indicate an oil spill, just sometimes a natural bubbling up from the sea floor,” Murray said.

According to an article from the Bamfield Marine Sciences Centre, methane can also come from “mud volcanoes” that release fluids and gases into the surrounding waters of the deep ocean, which can have methane content as high as 99 percent.

Methane gas seeps are relatively common in other places, although people are not accustomed to them here, Murray said.

“I’ve been diving up the coast of Santa Barbara, and you can smell it there pretty frequently,” she said.

Methane is a greenhouse gas, and can stay in the atmosphere for as many as 10 years.

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