Passed gas from bacteria is what we smell at seashore

To my Midwest-bred nose, the smell of the ocean hints of mystery, travel, adventure and romance. When I go to the beach, I take a deep breath and think, ah, love that salt air.

But that’s not salt I’m smelling.

When tiny marine animals graze on tiny marine plants (the base of the marine food web), some plant cells spill their guts in the water. Naturally occurring plant-eating bacteria view the spillage as a feast and chow down. As the bacteria digest these meals, they, well, pass gas.

The gas is a sulfur-based molecule called dimethyl sulfide, or DMS, and when we’re near the ocean, that’s what we smell.

Seabirds smell it, too. Some species, such as storm petrels, fly toward high concentrations of DMS because this is where the action is. It’s a good place to forage.

Research suggests that some seabirds also use the gas to navigate. Because underwater seamounts and shelf breaks influence currents, and those influence plant growth, variations in DMS density may be like maps for the birds. Navigating by nose may be a way seabirds find their tiny, remote island breeding sites.

The marine world has other distinct smells.

Low tides often give off a strong odor because rocks, reefs, sand and sediment trap dead and decaying fish and invertebrates.

At Molokai’s Papo­haku Beach recently, I spotted a fat sea hare rolling over the reef flat. It landed on the sand, and seeing the animal move, I picked it up to return to the ocean. Bad idea. The wiggle I saw in the creature came from escaping gas that filled its dead body.

Even after several saltwater rinses and sand scrubs, my hand smelled so bad I had to rub wildflowers on it to finish my beach walk.

Of course, anything dead long enough stinks, but dead fish and invertebrates have an aroma all their own due to an abundant, odorless chemical in their cells that they need to live in salt water. (Freshwater fish have it, too, but nearly not as much.) After a fish dies, air, bacteria and the animal’s own enzymes change the chemical to two others called amines. It’s the mixing of the two amines that give off that unmistakable fish smell.

Because amines are alkaline based, an acid-based substance neutralizes the smell. Behold the union of lemons and fish.

Some people tolerate the smell of fish better than others. One study showed that people who grew up near the ocean eating fish were far less repulsed by fish odor than those raised inland with little fish in their diet.

The latter would be me. Since fish was a rare meal in my Wisconsin childhood, I don’t crave it now and don’t like the odor of fish markets. My Seattle-raised husband, on the other hand, gets frequent salmon cravings and has an exceptional tolerance for fish smell. What I perceive as something stinking up the kitchen, he perceives as a mouthwatering meal.

Craig’s fondness of fish amines is nothing, though, compared with our little mutt, Lucy, who adores ocean smells. Her goal is to find a dead fish, roll in it and then scent her many sleeping spots in the house with her grand perfume.

Ah, love that passed-gas, dead-fish air.

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Reach Susan Scott at www.susanscott.net.