Why Does the Ocean Smell?

The Source of the Ocean's Smell May Surprise You

Smell is one of the most powerful ways to connect ourselves with memories, both good and bad. I was born as one of those "super-smellers." I can smell anything, even very faint, ranging from the scent of a friend that has passed in the hall to the smell of cigarette smoke wafting from the window of the car in front of me, driving at 40 mph. This gift can be both a blessing and a curse. I'm sure you can all think of smells that comfort you and drive you nuts. One thing is for certain, you don't have to be a super-smeller to enjoy the smell of the ocean.

I've always wondered what made that oceany smell. I live on the Chesapeake Bay, and at first I thought at first that it must be something related to marshes (or dead fish), but then I realized that the smell is the same on the shore of the ocean as it is here, with some subtle undertones and variations. Now I'm not one of those that wants to over-analyze the world so much that the magic is taken away; but, I do find magic in knowing what causes things, and being able to understand them. Knowing their cause doesn't make them any less wonderful. For me this is true for ocean smell.

The smell we're talking about is mostly sulfur, or sulfides. At first you might think it's simply seaweed decaying and making that sulfery stink. That's certainly part of it, but it's a bit more complex. Yes, seaweed can produce hydrogen sulfide when it dies and starts to decay, so can marsh plants; but ocean smell comes from much higher concentrations of plants in the water, namely phytoplankton (fi-toe-plank-ton). Phytoplankton are  super important tiny plants floating around in the water that are photosynthesizing or making food from sunlight. They are the base of the food web of the oceans, much like plants here on land. The crazy thing is, they're almost even more important.

Let's start with what they look like. Phytoplankton are microscopic producers. This simply means they are wee tiny plants that have green, red, blue, or brown pigments to help them make food from the sun. They have to float near the surface of bodies of water so that they can get sunlight. If they float too high in the water column they fry, and if they float too low, they die. There's a sweet spot for them that they want to be in. There are many shapes and sizes of phytoplankton. My favorite phytoplankton are called diatoms and they look like miniature stained glass windows.

To deal with sunlight, and living in water, phytoplankton have developed a chemical called dimethylsulfoniopropinate (die-meth-L-sul-phon-E-o-pro-pin-ate) or DMSP for short. This stuff is basically an all around antifreeze sunscreen for the plankton (remember they live anywhere from the waters of the Arctic to the tropics). It's also thought that DMS is used in something called osmoregulation (oz-moe-regulation), which is a fancy word for balancing the amount of freshwater in their cells with the saltwater they are floating in. If they didn't have this protection they could shrivel like a grape in the sun, or blow up like a raisin soaking in a bowl of water (try it, you know you want to).

When plankton die they are digested by bacteria. When the bacteria eat the phytoplankton they essentially convert the DMSP to something called DMS or dimethylsulfide (die-meth-L-sul-fide). Do you notice the name is shorter than dimethylsulfoniopropinate? This is because what the bacteria are doing is breaking apart, or cleaving, a methyl group off of the DMSP, splitting it up if you will. So why does this matter?

When the bacteria split the methyl group they release sulfur into the air in the form of hydrogen sulfide. This is what gives the ocean, and other marine bodies, their smell. The conversion of DMSP to DMS, and the release of sulfur, is part of something called the sulfur cycle (scientists love their cycles, you name it, there's a cycle for it, anything from the water cycle to the rock cycle). Now when sulfur is released into the atmosphere by the phytoplankton, that sulfur oxidizes (add an oxygen group) to form sulfur dioxide. Stick with me here....this is the complex sciency bit. These tiny sulfur dioxide aerosols start floating around in the atmosphere and sticking together. Eventually enough stick together to form particulates (called nucli) that are about the size of a spec of dust. When they get this size they are large enough for water vapor to stick to them. When water vapor accumulates then clouds form, which is part of the cloud cycle.

Phew...that was a lot of information, so let's review: plankton die, plankton get eaten by bacteria, the bacteria release sulfur into the atmosphere, the sulfur oxidizes and then starts forming very tiny clumps. These clumps then form water droplets and clouds. Make sense? Essentially ocean smell not only smells good, but it also helps to form clouds.

There's lots more neat science around this, and some scientists even think that maybe we could seed the oceans with fertilizer to make more clouds and help cool the planet or slow climate change.  Regardless, we have tiny phytoplankton floating around in the oceans (by the gigaton), that die and decompose, to thank for the smell of the oceans that is so distinct.