Gabrielle Nevitt remembers the first time she noticed the smell. It was sometime in the early 1980s and she was an undergraduate, heading out to sea on a research trip.
“Hey, can you smell it?” a fisherman said to her. “It smells like a productive area for fishing.”
She didn’t know what he meant at the time, but the odor has been a familiar part of her life for the last few decades. It’s hard to describe, but it’s unmistakably marine: Nevitt calls it “like oysters” or “kinda seaweed-y.” It’s the scent of dimethyl sulfide, or DMS—a gas that’s been described as a keystone molecule, because it influences everything from the presence of birds to the formation of clouds.
DMS is produced when microscopic animals graze upon the algae that grows near the ocean surface. Since it doesn’t dissolve easily in water, it eventually makes its way into the overlying air. That’s why passing sailors can smell it. Some of the gas rises into the atmosphere, where it seeds the creation of clouds. And other DMS molecules drift through the skies until they find their way into the noses of birds.
Tube-nosed birds—the albatrosses, petrels, and shearwaters—soar across the open oceans, relying on their keen sense of smell to find food. For them, DMS is intensely alluring. This attraction makes sense. DMS gives away the presence of clouds of plankton, and so acts as a loud dinner bell, telling the birds where meals can be found. Nevitt proved this in 1995 by sailing through the southern Atlantic and releasing oil slicks that were scented with either DMS or cod liver oil. Seabirds like white-chinned petrels, prions, and storm petrels flocked to the former over the latter.