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Once you’ve smelled the ocean, you can’t un-smell it.
That sort of sharp, sometimes eggy odor is just that distinctive.
And it also plays a big role in ecology and maybe even in the climate!
Because sure, there’s salt and that whiff of dead fish, but the key ingredient
in this smell is something you probably wouldn’t expect: exploding plankton.
Collectively, the tiny plant-like organisms floating in the
sunlit layer of the ocean are called phytoplankton.
And they, as well as certain bacteria,
make a chemical compound called DMSP.
Among other reasons, phytoplankton make DMSP
to help protect themselves from too much UV radiation,
balance the water content in their cells, and even deter predators.
But sometimes, no amount of this compound
will prevent them from being a tasty snack.
And that’s where the fun begins.
When something like a hungry predator comes along
and breaks open a phytoplankton cell,
the DMSP is released from the cell into the water.
And there, it becomes an important food source to microbes.
As the microbes graze on the DSMP, they ultimately break it down into
smaller molecules such as dimethyl sulfide, or DMS.
The “sulfide” part means it contains the element sulfur,
and that’s what gives the ocean its unmistakable odor.
It’s a bunch of microbes breaking down their food!
Now, in some places, this sea smell can be really pungent,
leaning towards the rotten eggs end of the spectrum—
while in other locations, you might barely catch a whiff.
The difference depends on how many phytoplankton live in the area.
Specifically, it takes a group of actively-growing phytoplankton,
called a bloom, to ultimately make a strong odor.
The larger the bloom, the more DMSP there is for microbes to break down,
and the stronger the sulfur smell.
And it’s not just humans that notice it.
Animals from seabirds to seals to whale sharks
will follow the scent to track down their next meal.
That’s because their prey, such as fish and zooplankton,
can often be found chowing down on the phytoplankton that make up a bloom.
But there’s actually another story here, too — because DMS in particular
also plays another, more surprising role on Earth: helping to form clouds.
DMS is the largest source of biologically-produced sulfur on our planet, and,
since it’s a gas, it quickly makes its way into the atmosphere.
On the way there, it goes through chemical reactions
to become a variety of sulfur compounds.
Then, these compounds act as condensation nuclei in the atmosphere,
which means they’re something water vapor can collect on to form a cloud.
And clouds can have a surprisingly large effect on the climate!
Like, fluffy white clouds reflect sunlight back to space,
which helps keep the planet cool.
At the same time, through the process of photosynthesis,
phytoplankton are also removing carbon dioxide from the atmosphere.
So, in a way, these tiny creatures are some of the Earth’s
most important climate regulators.
And the process is self-reinforcing: absorbing more CO2 means more energy
for bigger phytoplankton blooms, which then produce more DMS —
and more clouds — as a result.
Unfortunately, like other important climate processes,
things are starting to get a little out of balance.
As the oceans absorb more of the carbon dioxide we’re emitting,
they’re becoming increasingly acidic.
And that’s not good for phytoplankton growth or the production of DMS.
So, ultimately, scientists have a lot left to learn about the complex interplay
between the ocean, life, and our atmosphere, and how it will change in the future.
One thing is for certain, though: the smell of the sea is unforgettable.
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