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Why Is The Ocean Salty?

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

sulfate.

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

the oceans.