The fresh, salty smell of beach air is actually the smell of rotting seaweed.

(@UberFacts) March 20, 2015

The unmistakable smell of a fresh sea breeze is as synonymous with the British summer as melting ice creams, seagulls pinching chips and walking home with sand in your shoes. But its secret is a molecule and the bacteria that create it.

The mystery molecule is called dimethyl sulfide (DMS) and is derived from dimethylsulfoniopropionate (DMSP), a compound produced in huge quantities by phytoplankton – tiny single-celled marine animals – in all of the world’s oceans. Approximately one billion tonnes of DMSP is produced by the world’s phytoplankton each year.

DMS is found in other biological pathways and is said to give some foods a savoury taste. It’s scent is also so strong that most people can detect it at about 0.02 parts per million. It’s even sometimes inserted into gases so that we can smell when there is a leak.

Andy Johnston, a professor of biology at the University of East Anglia studies DMS, and identified the biological pathway from DMSP by culturing bacteria genes from mud found on a beach.

“I knew we’d isolated the right genes,” he told The Telegraph in 2009, “because the incubator smelled like a beach. When the concentration rose too high, it smelled like rotting cabbage.”

Bacteria feed on the phytoplankton, turning DMSP into DMS. The presence of phytoplankton indicates there will be more marine life nearby, as they are a food source for small fish. As a result the smell of DMS attracts seagulls and other animals that might want to feed on the fish.


The biological pathways is slightly different between the world’s oceans: “I can see that genes for one mechanism of creating DMS are abundant in the Galapagos Islands but not in other areas,” adds Johnston. “But the genes for a different mechanism are widespread in the Sargasso and the Pacific.”

So while it is the gas released by feeding bacteria that we’re smelling when we head to the beach, it’s really phytoplankton that we have to thank.

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