ABC Listen Hello, my name is Nige, and today on Imagine This, we're building sandcastles.
I like any old sand.
Yeah, me too.
Digging's fun.
Yeah, collecting shells.
That looks nice, pretty shells.
Yeah, i'm gonna add a moat, maybe a drawbridge, drawbridge oh, that's ambitious.
I can give it a crack, though.
This is thirsty work, and look at all that water.
I'm just gonna grab a quick drink From the ocean.
Yeah.
Can't hurt, right?
No.
Because it will make you seasick.
It tastes like seaweed and salt with water.
Yummy.
No.
It tastes like salt, but too salty.
Ah, but I eat salt with my food.
Yes.
Why can't I drink salt with my water?
It's liquid salt.
And some salt is bad for your body?
A little bit's fine.
And how'd the salt get there in the first place?
That's what George and Remy have been wondering.
Hi, my name is George.
I'm five years old.
My name's Rumi and I'm five years old.
And my question is, why is the sea salty?
Why is the ocean salty?
I use salt when I cook.
Maybe there's a big chef somewhere sprinkling salt in the water when we're all not looking.
Yeah.
Maybe you need to buy all the salt in the shop, open the package and throw it in the ocean.
No.
Maybe.
No.
We should talk to Dr. Katerina Fabricius.
Katarina is a coral reef expert.
So grab your goggles.
I reckon we'll find her at the Great Barrier Reef.
Cool.
We're on a rowboat.
Row, row, row your boat gently through the reef.
If you see an octopus.
Don't forget to scream.
This is paradise.
The water's so clear and blue.
I can see turtles down there.
I found a fish.
I can see a jellyfish right there.
Hang on.
What's that black shape in the water?
It's moving towards us.
It's a shark.
It's a seal.
Hi everyone.
The scientists.
You?
It's you Katerina.
You're in a scuba suit.
That's a big tank on your back.
So then she doesn't get any sea water in her mouth?
Yeah.
Is that how you breathe?
Yes.
These tanks are full of air so I can spend a long time underwater looking at the coral reef.
Can you see salt down there?
Salt?
Yeah, we want to know why the sea is salty.
Does the salt come from the coral?
No, the salt in the ocean doesn't come from the coral.
But I can help you find the answer.
Before we go down underwater though, it may be more fun to start right here on the surface.
But nothing's happening.
Oh, in the ocean something is always happening.
Let's imagine we are tiny drops of seawater floating on the surface of the ocean.
Yeah!
Let's go!
Whoa, it's crowded.
Oh yeah!
Every drop of seawater is teeming with life.
It's just so small you need a microscope to see it.
Lots of edibles and some seaweed.
Tiny little sand bits maybe.
Particles.
They're all swimming around.
Yeah.
Ocean habitats aren't just coral reefs or kelp forests.
Every single drop of water is home to billions of creatures.
So where's all the salt?
The salt's not a matter for us.
It's in here.
We just can't see it.
Even when we are microscopic.
That's because salt dissolves in water.
You only see salt when it's like big salt, like it's covered in our food.
Yeah.
Because it's really tiny.
Because it's a bit safer.
Because it gets...
It disappears.
It gets so swished and it can go invisible.
It dissolved!
That's right.
To be able to see the salt, we need to take the water out.
That's not possible.
There needs to be a giant... sponge and then we'll soak up the whole ocean.
The ocean's too big.
It's too much water.
Yeah, that sounds like a lot of work.
Lie back little droplets and see what happens.
This is lovely.
So relaxing.
It feels nice.
Every drop of water is made of billions and trillions of water molecules.
The sun's shining.
I feel warm and weightless.
Hang on.
I really am weightless.
Am I flying?
We're going up into the sky.
We're evaporating.
Evaporating?
When the sun shines on the ocean, the water on the surface gets warmed up and the heat gives those tiny water molecules the energy to change.
Do feel kind of energised.
How does the water change?
Some of the water molecules start to move away from each other as they change from a liquid into a gas.
Like this!
Not that kind of gas!
It's called water vapour.
Just like the steam coming out of a boiling kettle, the warmer molecules of water have energy to move.
Evaporation means tiny bits of water are breaking free from the surface and moving up into the air.
Are we salty water vapor? since we've evaporated from the ocean?
I don't taste salty.
I don't taste salty.
No, salt is heavier than water.
It's too heavy to evaporate and float up into the sky.
So salt gets left behind in the ocean and just the fresh water vapor rises out of it.
So where are we headed?
The clouds.
The clouds are so beautiful up here.
They look nice and fluffy.
They feel like fairy floss.
I think they are made of fairy floss.
But white fairy floss, you know, they're made out of air water, tiny little raindrops.
Clouds are made of water vapor, but it's so cold in the sky the molecules lose all that energy they get from the sun heating them up and they start to move back together.
Let's hide them together and stay warm.
So one single molecule of water is really really, really tiny.
But if more and more and more molecules get together, they get bigger until they change from the gassy water vapour back into drops of liquid water.
Uh-oh.
We've done this part before.
The water molecules stick together to become raindrops.
Once they're too heavy to stay in the sky, They fall as rain.
While it's moving through the air, fresh water picks up a tiny bit of carbon dioxide.
What's carbon dioxide?
We breathe in oxygen into our bodies and breathe out carbon dioxide.
Yeah, exactly.
Carbon dioxide exists in small amounts in the air.
Is the carbon dioxide salty?
No, but it does make rainwater a little bit acidic.
Huh?
Acid rain?
Only a teeny tiny little bit.
We're falling in a river!
We're landing in a creek!
Oh, a frog in a tadpole.
Hi, froggy.
Remember how I said the rain was a little bit acidic?
Yes.
It means the water can dissolve some of the stuff that is inside rocks, like salt.
But this water isn't salty.
It's still fresh.
It's not salty like seaweed. because it's on the move.
Fresh water collects on land, in creeks and in rivers, and then it flows downward towards the sea, carrying all those little bits of salt from the rocks as it goes.
It's called erosion.
Yeah, exactly.
Water can even seep underground and collect salt from rocks there too.
Now, the amount of salt that would dissolve into the water from one river is not enough to make the water salty.
But, water on Earth is incredibly old.
It's been going from the ocean to the clouds, to the rivers and underground and back again through this water cycle for billions of years.
We're back in the ocean.
Now we're salty!
We're salty water.
All the salt can go everywhere, all around in the sea.
Yeah.
So when fresh water washes over rocks, it picks up a tiny bit of salt.
And that gets carried in streams and rivers all the way to the ocean.
Because all the little bits of salt are moving to the ocean.
But when the seawater evaporates to make more rain, the salt gets left behind, making seawater salty.
Yeah, that's it.
The sea is salty because of what?
Hey, rocks really do rock!
Salt is always being added to the ocean and only the fresh water is ever taken out.
It's been happening for such a long time that now There's about six teaspoons of salt in every litre of seawater.
No wonder it tastes bad.
That's a lot of salt.
Is it the same salt that we eat on our food?
Yes, we do eat sea salt.
Now we're going on dinner!
In Australia, most of the table salt we eat comes from evaporating seawater.
How?
In just the same way.
The sun heats up the water, the freshwater floats up into the sky and the salt is left behind.
Then people come, collect it and box it up to send it to the supermarket.
If the salt water is bad for us to drink, is it okay for all the fish in the coral?
Corals can handle the salt.
The fish and other sea animals too.
Their bodies are different to ours.
Most sea animals actually need the salt.
They would die in fresh water.
The changes I see in the coral reefs are from what humans are adding to the water cycle, not the salt.
We need to look after Mother Nature by keeping it clean.
I took some plastic out of the ocean yesterday.
Lovely.
Whatever goes into the freshwater on the land, through our rivers and streams, through our farmlands and even down our kitchen sinks, all of it eventually makes it down to the ocean, And it can stay there for a long time.
Wow.
So fresh water and salt water are connected.
Through the water cycle.
Yeah, exactly.
Thanks for taking us into the sea and the sky, Katarina.
Anytime.
Thank you.
Bye.
Bye.
So, George and Remy, when water flows over rocks, little bits of salt dissolve from the rock and mix into the water.
That's called weathering.
The salt is carried through streams and rivers all the way to the ocean.
It's called erosion.
Where it stays. because it's too heavy to become rain again.
It can't evaporate.
This is part of the water cycle.
For billions of years, water has been moving from the oceans to the clouds, raining into rivers, moving underground and washing back into the sea, slowly carrying more and more salt into the ocean and making our seas salty.
Imagine This is an ABC Kids Listen podcast.
For more podcasts to play, music to move and stories and soundtracks for sleep.
Download the ABC Kids Listen app free from your app store.
