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C. Scientists Discover a Major Source of an Ozone-depleting Gas

Narrator: This is Science Today. It's been discovered that salt marshes are a major source of methyl bromide, a natural and industrially produced gas. Robert Rhew, a researcher at the Scripps Institution of Oceanography, says scientists knew more than half of the methyl bromide in the atmosphere came from the oceans, fumigation and vegetation burning - but there was still a significant balance that was unaccounted for.

Rhew: So this big missing source - we went out to look for it and one of the places we looked for was salt marshes because salt marshes are areas of high, primary productivity. And it turns out that salt marsh vegetation - or something intimately associated with the vegetation - it's producing methyl bromide and methyl chloride like gangbusters.

Narrator: Because these compounds deplete the ozone, controls to regulate its production have been developed. But Rhew stresses salt marshes are not bad for the environment. In fact, they play a vital ecological role. The key is balance.

Rhew: We're getting closer to understanding the global budget of these compounds, which will in the end affect our decisions on how to regulate it internationally.

Narrator: For Science Today, I'm Larissa Branin. .