What Gives the Ocean Its Wonderful Smell? A Vile Chemical

Ah! It's summertime, and those of us who happen to be "ocean people" just can't get enough of the wonderful smell of Mother Ocean. It doesn't much matter which ocean you're near. The "ocean smell" is universal. 

When chemists hear the word "smell," we also think "chemical" because 1) we're deeply disturbed individuals; 2) scents result from a specific chemical or mixture of chemicals, and we wanna know what it is.

The pleasant smell of soil, when it first starts to rain, is due to geosmin, a simple organic molecule that people can detect at extremely low concentrations. The ghastly vomit-like smell of ginkgo berries is caused by butyric acid, giving vomit its lovely bouquet. And the beloved smell of the ocean is due to...dimethyl sulfide, one of the most disgusting odors ever to haunt chemistry labs. Or your underwear. Dimethyl sulfide (DMS) is one of the fart gases, among other things. 

The chemical structures of geosmin, butyric acid, and dimethyl sulfide (from left to right).

Whenever I write about a nasty chemical, I always look for a quote from Derek Lowe, whose In the Pipeline blog is the place to go for up-to-date information on chemistry, the pharmaceutical universe, health issues, and also humor. (His "Things I Won't Work With" articles are hilarious and very widely read.) The following quote isn't about DMS itself but something that formed when he mixed it with an organosilane and inadvertently made something even worse) but it's pure gold: 

When these [chemicals] two came together, they produced something that seemed to have come from a robot with gastrointestinal issues. I was not prepared for this synergistic symphony of scent, and nearly dropped the flask.

Derek Lowe in Chemistry World

But one of his readers chose to accentuate the positive (dimethyl sulfide itself):

"You'll have no problem finding a seat on the bus if you are working with dimethyl sulfide."

"Elinker" in Science Blogs

There are plenty of chemicals with pleasant scents at low concentrations but jump ugly on you at higher concentrations. One of them is called skatole – the principal odor of feces. Tiny amounts of skatole are used in perfume, but if you open a bottle of the stuff and stick your nose in there (not recommended), it's "Howdy Doody Time." (Some idiot who, by an astounding coincidence, happens to work at ACSH tried this once. But not twice.)

Democrat Point, Fire Island National Seashore, NY

Where Does Dimethyl Sulfide Come From?

Given that DMS is what gives the ocean its scent, it is not at all surprising that it comes from marine algae. DMS is a metabolic breakdown product of  3-dimethylsulphoniopropionate, an osmolyte, which algae biosynthesize in order to maintain a constant volume of water in the cell (1). When it breaks down, dimethyl sulfide is released in huge quantities. 

By Air and By Sea

DMS is the largest source of sulfur in the atmosphere. Scientists from the Leibniz Institute for Tropospheric Research have been estimated that marine algae produce 10 to 35 million metric tons of atmospheric sulfur, mostly DMS, which is thought to connect the ecosystems of the sea and air. DMS plays a part in the formation of clouds that block solar radiation from hitting the earth; sort of an anti-greenhouse gas. 

Which brings us back to the beach. You now possess the knowledge to deflect blame should you toot one out in the company of others. Blame the ocean. But if anyone pins it on you anyhow, just say that you're doing your part in controlling global warming, and all should be good. 

NOTE:

(1)  3-Dimethylsulphoniopropionate has multiple functions in protecting algae. See Evolution of Dimethylsulfoniopropionate Metabolism in Marine Phytoplankton and Bacteria