Hey, ocean, what’s with all the salt?
Hi everyone, Julian here for DNews at YouTube Space LA. Recently we got a question from
NENE71984 asking why the oceans were salty, and everyone in the office kind of looked
at each other and went, “Yeah, why?”
I’m going to assume she’s not asking why the ocean is all sassy and bitter, but instead
is asking why there’s salt in the oceans but not in our lakes and streams. Except some
lakes like the Great Salt Lake, I know, people in Utah and internet trolls. Jeez, I always
have to be technically correct with you guys, the best kind of correct.
First off the salt in the oceans is 90% the same chemical makeup as your table salt, good
old NaCl. Sodium Chloride isn’t the only kind of salt there is, there are many varieties
because a salt is just a compound held together by an ionic bond. What happens is an atom
steals an electron from another and becomes negatively charged or an anion. Then it’s
attracted to the positive cation and the two atoms bond. So a lot of different chemicals
can come together and make salts, and because of this the ocean salt is also made of a little
magnesium, calcium, potassium, and a polyatomic anion made of sulfur and 4 oxygens called
But how does the salt get there? From the rocks on land, actually. According to the
US Geological Survey, dissolved CO2 in rainwater makes it slightly acidic, eroding rocks when
it falls. That’s not the only trick water has up its sleeve. And H2O molecule is polar,
the oxygen atom hogs the electrons so it’s more negatively charged on one side and more
positively charged by the hydrogen atoms. When salts are in water, they break apart
because the only thing holding them in their crystalline shape was that ionic attraction.
Once the rain lands, it flows downhill, carrying the dissolved minerals and ions to streams
and lakes and rivers and eventually the oceans.
The USGS also points out salt comes from inside the ocean too. Volcanoes and hydrothermal
vents heat water so it can dissolve some of the basalt on the ocean floor, adding salt
to the mix.
But why does the ocean stay salty? Because salt has been accumulating there faster than
it leaves. Some organisms use the salt or the basalt on the ocean floor takes some back,
but the exchange rate isn’t even. There’s also the factor of evaporation. When water
evaporates, the molecules spread farther apart and the magnetic pull from the vapor isn’t
enough to bring the ions with them. As a result, the salt stays behind and it rains fresh water.
So long as the water doesn’t get stuck inland a la the Great Salt lake, salinity levels
will stay below .05%, compared to the 3.5% average salinity of