I posted on this years ago, but the post below about submerged dead zones prompted me to reprise this.

A few years back, my friend Bill Tait was sailing his 40′ ketch Sinisterre home from the St Pete-Cancun race, when suddenly the sea around him erupted into a bubbly effervescence, like champagne. The water which had a moderate sea running at the time, became glassy and smooth and bubbles could be seen coming from below.

For a while, they feared there would be so much foam the yacht would lose buoyancy and sink into it and be swallowed up without a trace. The condition lasted for some minutes, long enough for the boat to sail several miles, and then Sinisterre suddenly emerged from the strange flat water and into an ordinary sea.

Tait took a fix and determined the vessel was over the edge of the continental shelf, in about a hundred fathoms of water. He is a graduate geographer, so he emailed some of his professors at USF about the incident, and later showed me the correspondence.

The best theory they came up with was that a shelf of porous limestone saturated with methane in solution had collapsed on the continental slope, and an underwater avalanche exposed some strata, releasing the gas. As the gassy water roiled toward the surface, the pressure drop forced the methane out of solution, like removing the cork in a bottle of champagne.

One of the profs quipped that it was obvious no one aboard was smoking!