- [Caitlin] Under the ice in Antarctica, there is a world that few people ever see.

- [Paul] It's just one of the most beautiful things in the world.

- [Rob] It's really hard to describe.

- [Steven] Every time I come down here, every year I always find something I haven't seen before.

- [Paul] It's just a place teeming with life.

(gentle music) - [Rob] I promise you, like, I don't go in the water without going "Holy crap, I get to do this!"

- [Arlo] How do I help?

Today I'm helping Rob Robbins and Steve Rupp.

They are some of the most hardcore people we've ever met, because they dive underneath the Antarctic ice.

- It is spectacular.

There's no diving like it anywhere else.

There's been a lot more astronauts than there have been divers.

We can think of about 395 people have dove in Antarctica, and there's been almost 600 Astronauts.

- Where's mine?

- Oh it's that pink one there.

- [Arlo] When scientists aren't trained, or are too busy to venture below the ice, they rely on Steve and Rob.

- [Arlo] So that's your emergency oxygen?

- Yeah, and it's kinda at the safety stop level.

- Groups come down, and we do their diving for them.

- And our job is sampling, leaving instruments, collecting stuff that they've left over the years.

- Now the hard part!

- The floors keep getting lower.

(upbeat music) - [Arlo] Under the ice, there's this whole world of bizarre organisms that have fascinated scientists for decades.

Ribbon worms, ancient sponges, giant jellyfish.

These are just some of the creatures that make this place feel like it's straight out of a sci-fi movie.

- [Caitlin] It's a baby, a baby Antarctic sea star.

I've come to the McMurdo Aquarium.

So many alien-like creatures in here.

To figure out why scientists are so interested in life under the ice.

- So this one is actually pretty small, it's about like 30, 40 pounds.

- [Caitlin] That does not look small to me, what is it?

- [Chi-Hing] It is called the Antarctic toothfish.

- [Caitlin] Gosh, and you guys catch these for research?

- [Chi-Hing] We catch these for research.

- Look at this guy.

This guy is huge.

Hey come back here!

- [Chi-Hing] Come back!

- [Caitlin] This water is so cold that I feel like my hand's going to fall off.

- It is freezingly cold, yes.

- Really, really cold!

- [Caitlin] And this makes me wonder.

- [Zachary] Did you touch it?

- [Caitlin] I touched it.

- [Zachary] I can't see, you gotta do it again.

- [Caitlin] I can't do it again!

How can these fish possibly survive?

Turns out, that's part of what Paul Cziko is studying.

Because fish really should be frozen in this water.

- So this is 28 degree Fahrenheit water, it's right at its freezing point.

- [Caitlin] And to understand why?

- Some of the coldest water on the planet.

- I gotta stick my hand in this water again.

- The goal here is to see how long you can keep wiggling your fingers.

- Can this, like, permanently hurt me?

- No, 'cause you're a warm blooded animal.

- [Caitlin] The salt in the ocean water causes it to freeze at 28 degrees Fahrenheit.

Four degrees below the freezing point of fresh water.

- [Paul] Are you wiggling?

You're not wiggling.

- [Caitlin] I am wiggling!

- [Paul] You're opening and closing!

(laughs loudly) - [Caitlin] This hurts.

- You're at 33 seconds!

- It hurts so much!

But it shows that I am a warm blooded animal.

My body fights to keep me the same temperature.

That's why I could stick my hand in this water for some time and Paul.

- Can I do a minute?

- [Caitlin] Well, for a bit more time.

- I think I can do a minute.

- [Caitlin] But fish are different.

Most are cold blooded, so they become the temperature of their surroundings and that's the problem.

- So any fish that you throw in here should be frozen solid.

Right, if they touch ice they should just freeze and die.

- [Caitlin] Instantly?

- Yes pretty much instantly, within a few seconds.

- [Caitlin] Why so fast?

- Because they're below their freezing point.

Ice wants to grow.

So if you touch them with ice, a normal fish, it would freeze solid instantly right?

- [Caitlin] I didn't get it.

Why should touching ice cause the fish to freeze instantly?

And then why don't they?

- These tubes are, they're about at 24 degrees Fahrenheit.

- [Caitlin] To show me what's going on, Paul sets up a demo.

- So let me go get a tiny bit of snow from outside.

- [Caitlin] When he drops a bit of snow into the test tube of water, the entire thing freezes in seconds.

This happens because the water is supercooled.

- So liquids exist below their freezing point without freezing.

And you can take a bottle of pure water that you buy at the store and put it in your freezer.

It'll get down to, I don't know, 10 degrees Fahrenheit or so, but it'll be liquid until you touch it with a piece of ice.

- [Caitlin] For the ice molecules to arrange into a crystal structure, they need a nucleation site.

A place where the crystallization is triggered.

In the first demo, a small piece of ice was that trigger.

But here's where it gets interesting.

- So these fishes are from the environment.

They have ice in their body.

Just naturally, naturally occurring ice that exists in the environment, that has somehow gotten into their body.

- [Caitlin] So when Paul takes a tissue sample from one of the Antarctic fish, it also freezes instantly!

- [Paul] Did that fish have ice in it?

- [Caitlin] Yes!

- [Paul] Yes, and how do you know?

- [Caitlin] The whole test tube froze, immediately.

- [Paul] The whole test tube froze.

So the ice crystal in the fish seeded this tube, and it grew ice.

- [Caitlin] But if all these fish are cold blooded, have ice in their bodies, and are swimming in water below their freezing point, why aren't they frozen?

What's going on?

- [Arlo] To find out, we head out on a specimen collecting expedition.

Or, in other words.

- This should be a nice relaxing fishing trip right?

(laughs) - You couldn't even say that with a straight face!

(upbeat music) - [Arlo] Paul's actually one of the scientists who can do his own diving, but sometimes... - Fishing here is so easy.

(laughs) - [Arlo] The low tech solution is best!

- From the surface we often drill 10 inch holes, through eight to 15 feet of ice.

Drop a line in with a little hook.

We often use these little Snoopy poles that you you buy at Wal-Mart or whatever.

- Woo, 80 feet is way longer than I expected.

- The fish here are actually really easy to catch.

- Oh no is it?

- You don't need to hold it higher, just reel faster.

- The fish that we study most here are the notothenioids.

So this is a group of fishes that dominates the coldest regions around Antarctica.

And they all descend from a common ancestor that evolved the solution to the problem of freezing.

(engine revving) - And there's one man who knows this better than anyone, Art Devries.

So I felt a bite, how do I tell if it's still on there?

Around here.

- [Arthur] Drop it to the bottom once.

- [Caitlin] Art is a legend.

You've been doing this for a long time, huh?

- [Arthur] Yeah, I started out in, what was it 1961.

- [Caitlin] Wow, over 50 years.

- Yeah in those days we had to cut the holes with chainsaws.

(chainsaw cutting) - [Caitlin] Art's the one who cracked the case of how these fish survive.

- [Arthur] As you can see, there are lots of ice crystals around.

Lots of ice.

So they've evolved this antifreeze protein which recognizes the ice crystals, binds to it, and prevents it from growing.

- [Caitlin] You heard that right.

Art discovered that these fish have antifreeze!

But, it isn't like the antifreeze in your car.

These fish have a special kind of antifreeze protein.

- Look at it like putting a hairnet.

It encases the ice crystals and prevents them from growing.

- [Caitlin] Under the microscope, you can see the difference between a particle of ice with and without the antifreeze protein.

On the left, ice is growing normally in water.

But on the right, the ice has antifreeze proteins binding to it, arresting its growth.

These same proteins bind to the ice crystals in the fish bodies, and that keeps that ice from growing and freezing the fish.

This allows fish to swim in ocean water that is a couple degrees below their freezing point.

It doesn't sound like much, but it's all they need to stay alive.

- All right, got some dinner!

- [Caitlin] Well, almost all they need.

- Or a science experiment, you know!

- They're full of parasites, I'm not sure you want to eat 'em.

(laughs loudly) - Oh, there we go, ayyy!

- Yayyy!

- [Arlo] We're catching these fish so Paul and Art can study what happens to all those accumulated ice crystals in the fish bodies.

- So they actually accumulate ice crystals in their bodies over their lives.

And these ice crystals are just there.

They don't grow because they're covered with antifreeze proteins.

- Are there any real world applications for these antifreeze proteins?

- You mean besides keeping the fish alive?

- Practical applications!

- One company has been putting fish antifreeze protein in ice cream.

And that keeps it nice and creamy and smooth.

- [Arlo] While, for Caitlin and I, this is clearly the most important outcome from studying these fish.

These antifreeze proteins also play a surprisingly vital role in making Antarctica what it is today.

- There's a lot of other parts of the food chain that depend on these fishes.

The penguins, and the seals, eat notothenioid fishes.

If these fishes hadn't evolved the mechanism to avoid freezing, they wouldn't be here.

- [Caitlin] It's mind-blowing to think that these weird looking fish make life in Antarctica what it is today.

(gentle music) (mumbles) (electronic whooshing)