All that salt water that makes up our ocean doesn’t actually contain any salt,
which seems ridiculous, but it’s true...and the reason why is crucial to how our planet works.
Welcome to MinuteEarth. Salts are chemical compounds made
of positively- and negatively-charged particles called “ions” like sodium and chloride, which make
up the salt crystals we’re most familiar with. But salts generally can’t exist in water - at least
not for long. That’s because water molecules have a negatively-charged end and a positively-charged
end, making them work like tiny magnets that tear the salt’s positive and negative ions apart;
that’s what’s happening when you dissolve a bit of table salt in a cup of water. Even though we’d
call what’s in the cup “saltwater,” there’s no salt in it - just ions. And the concentration
of those ions is what we’re really talking about when we measure the “salinity” of water.
If you added lots more salt to your cup, you’d reach a point where there
would be so many ions that they’d bump into each other and re-crystallize faster than
the water molecules could tear them apart, causing actual salt crystals to start piling
up. That recrystallization occasionally occurs in nature, like in the Dead Sea,
where ions are constantly being washed into the ever-evaporating lake with nowhere to go.
But in the ocean, even though ions are constantly being added – from volcanic activity above and
below the ocean, river discharge, and dissolving seabed sediments – there’s not only way more
water around to dilute those ions; ions are also constantly getting removed. Some end up on land,
some are taken up by sea life to do stuff like build shells, and lots get absorbed by
hydrothermal vents and incorporated into Earth’s crust. As a result, the overall concentration
of ions in the ocean - its “salinity” - has remained pretty constant over time.
And those ions help keep our oceans humming along. As seawater at the poles freezes into ice,
ions get left behind in the water, increasing its density. That water sinks below less ion-rich,
less-dense water, which in turn pulls in warm seawater all the way from the equator
to take its place. This exchange moves nutrients and oxygen all around the world
and helps warm the poles and cool the equator. But as the planet warms and the polar ice caps melt,
the ion concentration in the water at the poles has started to drop.
So far, the change has been small, but continued changes in ion concentration
could stop the ocean’s water exchange altogether; marine life as we know it would cease to exist,
the poles and equator would become uninhabitable, and hurricanes would feed off all that
equatorial heat, morphing into super-storms. If we want to avoid this apocalyptic scenario,
perhaps we should take our planet’s safety with a grain of salt and keep an eye on its ions.
And to slow down the warming of the planet, we should also keep an eye on our carbon emissions,
which you can do with our sponsor, Wren. With a little information about your habits and
lifestyle, Wren calculates your current carbon footprint and makes all sorts of suggestions
about how to reduce it. Wren also allows you to offset the carbon that you do release by making
a monthly contribution towards projects like this one, which turns wildfire-burned trees
into natural crop fertilizer. And for each of the first 100 of you who sign up using the
link in the description, Wren will plant 10 extra trees per person. Thanks, Wren!