Original subtitles

Our planet is the greatest living puzzle in the universe.

A collection of worlds within worlds.

Each one a self-contained ecosystem bursting with life.

But how do they work?

The intricate web of relationships

and the influence of natural forces

makes each microworld complex and unique.

So to discover their secrets, we need to explore them one by one.

Untangle their interlocking pieces

and ultimately reveal the vital piece,

the key to life itself,

hidden deep within each of nature's microworlds.

Our most northern microworld sits well within the Arctic Circle.

The Arctic, at the top of our planet,

is covered in a permanent cap of ice.

This close to the North Pole, the sea is nearly always frozen.

Temperatures can be well below minus 50.

In winter, the sun does not rise for three and a half months,

staying just below the horizon

and casting everything in an eerie blue half-light.

Even when the sun does appear above the horizon,

for much of the year, the rays are too weak

to be any use for primary production.

But there is one area of the Arctic Circle that's different -

our microworld of the extreme north,

Svalbard.

It looks barren,

but in Svalbard there are more polar bears than humans.

It is home to the most northerly population

of large herbivores in the world,

and for its latitude, it's unusually rich in life.

So what makes Svalbard so different to the rest of the Arctic?

To understand this, we need to look at what makes this microworld tick.

Unravel the working parts that make this place so special,

both the animals and the environment.

And to do that means understanding how the animals that live here

manage through the seasons.

When looking at the animals in this microworld,

the best place to start is at the very top.

How can a place seemingly locked in ice

support so many of the world's largest land predator,

the polar bear?

The bears hunt out on the thick sea ice.

But if the weather gets too bad to hunt,

which it can here for weeks, the bears have the ability

to curl up and slip into a sort of mini-hibernation and ride it out

without doing too much damage to their energy reserves.

This trick can be the difference between life and death.

And the reason they patrol the sea ice is the type of food they eat.

Their favourite food is the ringed seal.

The ringed seal can live out on the ice all year round,

using their claws to keep holes open in the ice,

so that if danger appears they have an escape hatch.

To be able to survive in this freezing water,

the seals put on a thick layer of warm, fatty blubber.

And this energy-rich blubber is what the bears are after.

But their problem is getting their paws on it.

The seals give birth to their pups out on the freezing ice.

A risky business with bears about.

Bears use their nose to find food.

They can pick up the scent of a seal buried under a metre of snow

from nearly a kilometre away.

They are the apex predators, the kings of our microworld.

Weighing up to 1,000 kilos, they can run at up to 60 kilometres an hour.

The bears might be king out here

but only 2% of bear hunts are successful.

But with a food source this rich,

a 2% success rate is just enough to survive.

With an estimated population of 6 million ringed seals,

predation is just nature's way of keeping the system in balance.

Predators keep prey populations fit and healthy

and to live here, you really do need to be fit and healthy.

The bears walk such a thin line

that they only eat the blubbery, energy-rich parts of the seal.

Not wasting time on the other parts of the seal that don't give them

the maximum return for their effort, before moving on to find more.

And this means there are plenty of leftovers.

Arctic foxes have learnt that following polar bears pays off.

The foxes clean up the meat that the bears don't bother with.

It seems counter-intuitive

but if you're an arctic fox, out here the best place to be

is right behind one of the world's most dangerous predators.

Without the bears and their picky habits,

the foxes would struggle to survive.

The bears have shown us how they do it at the top,

but what about the bottom of the food chain?

Where are the primary producers?

To find them, we have to follow

another of Svalbard's tough winter residents.

Reindeer.

Our microworld has the most northerly population

of large herbivores in the world

and they're literally scraping to get by.

These reindeer have evolved into a subspecies.

Unlike their mainland cousins, they are able to digest

enough of the tough vegetation they find here in winter to survive.

They also have shorter legs, longer fur,

and most importantly, the ability to put on thick fat reserves.

These adaptations are great for the cold

but mean they are not good runners,

which sounds disastrous with polar bears about,

but actually, the bears very rarely hunt them.

There is vegetation here underneath the ice

but it's hard to get to

and conditions here are too harsh for most plants.

For the reindeer of Svalbard,

starvation is the main cause of death.

To survive here, the reindeer, just like the ringed seals,

have to depend on their fat reserves.

But you can't build up fat reserves with such little food,

so there must be times of plenty.

And that is one of the things that makes Svalbard

so different to other Arctic locations.

Because, for just eight weeks of the year,

something truly fabulous happens in Svalbard.

Summer.

Spring and autumn do happen,

but the sun stays so low in the sky, its rays only skim the surface

and lack the intensity needed to be of any use to the primary producers.

But as summer gets closer, the sun rises higher in the sky,

the temperature increases and the sea ice starts to melt.

It's the signal for millions of sea birds

to fly in from the south to breed.

The short summer means that by the time they have arrived,

found a mate and hatched their eggs, there will only be three weeks left

to rear their young before they have to head south again

before winter once more closes in.

So how do they manage this so quickly?

Well, the answer is that summer here has 24 hours of sunlight a day,

and they use every minute of it.

Both the males and the females

bring food back to their growing chick almost constantly.

The threat of the returning ice is an ever-present deadline.

They have become absolute specialists

in collecting as much food as possible, as quickly as possible.

These guillemots can dive to 130 metres

and hold their breath for up to three minutes in the search of food.

But why, if there is such a tight time limit,

do they come to Svalbard in the first place?

The first things to react to the winter's weakening grip

are tiny organisms called phytoplankton.

They combine the sun's light

and carbon dioxide found in the sea water

to photosynthesize like plants

and they start doing this even under the ice,

forming a greeny-brown crust.

And as more sea ice melts and the sun gets higher in the sky,

the phytoplankton blooms on a monumental scale.

These are the marine equivalent of grass and are the primary producers.

And these feed the next link on the food chain,

millions of crustaceans,

which move around grazing like tiny underwater cows.

They feed the fish, which feed the birds and the seals

and so on right up to the top,

the polar bear.

The melting ice is good news for most,

but not for the bears.

This is the start of the bears' lean times.

Now it is their turn to rely on their fat reserves to survive.

Their Latin name means "sea bear", but without the sea ice to hunt on,

the advantage has turned to the seals fishing out in the open sea.

But all this disappearing snow and melting ice has a positive impact

on almost everything else within our microworld.

As the ground thaws, plants burst into life,

joining in the sprint to cram a full life cycle

into this tiny window of opportunity.

The most prolific meadows are found below the sea bird colonies,

fed by the tonnes of natural fertiliser

in the form of bird droppings.

So even Svalbard's flowering plants

are directly benefiting from the rich seas surrounding this island.

As do the reindeer, that come to these meadows

to feed on the new energy-rich growth fed by the bird colonies.

The reindeer are in the same race as is all life here,

to make the absolute most of summer.

This is their only chance to build the fat reserves

they will depend upon to see them through another winter.

Nothing distracts them.

Although feeding so close to the bird colonies has its dangers.

Arctic skuas, ground nesting birds,

don't take kindly to big clumsy reindeer near their eggs.

Their sharp beaks can cause real damage.

The problem is the reindeer are not really built to run.

They are so specialised to cold weather

that even the shortest run leaves them hot and bothered.

The areas around the bird colonies are also a focus for the foxes

which are also snatching this once a year chance

to raise a family.

And with eight hungry mouths to feed, it's a relentless job.

But winter will come around so fast,

that even with both the male and female working flat out,

it's likely only two cubs will survive to become adults.

Although there might be a lot of food

in our arctic microworld right now,

it's apparent that in this boom and bust ecosystem

these animals are not rolling in the good times,

they are gambling on the short summer to provide.

So how do the animals here cope with pressure like this?

Well, they are forced to take risks,

and as the days once more get shorter,

the hungry bears start to take some big risks.

Without the ice, they have no way of getting to the seals.

It is hard to imagine a polar bear meeting its match on land,

but at times, desperation drives the bears

to take on some unusual opponents.

Walruses can be three times as heavy as an adult polar bear.

Their tusks can weigh up to 10 lbs and measure a metre long

and with one and a half tonnes of mammal behind them,

they also make formidable weapons.

Apex predators, like the polar bears need to be on top form to hunt.

They need to use their energy wisely,

balancing the risk they take against the reward they stand to gain

from a successful hunt.

The polar bear might be king of our microworld

but even he lives his life on the edge at times.

And on this occasion, the gamble has not paid off.

All the animals have to balance the potential benefit

against the possible loss.

In general, the rewards outweigh the risk,

but there's a fine line that separates success from failure.

And if you've only got three weeks to rear your young,

winter coming a week early would spell disaster.

So the birds here are balancing right on the edge.

So why do they take the risk?

Well, its because Svalbard is unique

and for this short period, there's a lot of food guaranteed.

But they have to get out of here

before the ice returns in a matter of days.

And this means pushing your child off a 300-metre cliff

before it can fly.

The adults follow them calling all the way.

But it's a long way down

when they've never tried their wings before.

Getting to the water is only the first challenge.

With winter now approaching fast, they've got to leave.

The trouble is that where they want to go to is 1200 miles away

and the only way to get there is to swim.

Some don't even make it as far as the sea.

Soft bodies and feathers mean they can literally bounce

without sustaining serious injury.

But they do have to finish the last bit on foot.

And some land a long way from the sea.

And in a microworld on a deadline, not everyone can win when gambling.

When life is so finely tuned,

one creature's loss is another's gain.

For this family of foxes,

this final feast could be the difference

between surviving this year's winter and not.

Even with eight hungry mouths to feed,

the foxes can't eat all the birds they collect so they store them.

These larders full of food

help the foxes hedge their bets against the winter

when there's nothing else to eat.

With such long, light days, you can get a lot done.

So is this length of day

the key to a high level of productivity in our microworld?

Sunlight after all is the origin of all energy on Earth,

converted into food by those that can photosynthesise,

like those phytoplankton off Svalbard's coast.

All the other areas this far North have the same amount of sunlight,

but only the waters around Svalbard can claim to be responsible

for 50% of the Arctic's entire primary production.

So what is going on here that makes this place so special?

We need to know what phytoplankton gets in Svalbard

that it doesn't get anywhere else.

Besides sunlight, the phytoplankton also needs

other substances like nitrates and phosphates to flourish,

and these are hard to find at the sea's surface.

This is because they generally sink to the bottom and stay there.

So how do the primary producers get at it

if it's all trapped at the bottom of the sea?

Incredibly, the answer to this crucial question

comes from the Caribbean

and it holds the secret to what makes Svalbard so different.

A major force in the Atlantic is the Gulf Stream,

a flow of warm water that moves from the south of Florida,

north up the coast of America, crosses the ocean

and helps to keep the UK and northern Europe warm and wet.

Its most northerly arm reaches Svalbard,

warming the waters in our microworld by only a few degrees

but enough to help melt the ice.

This warm current collides with cold water flowing from the Arctic

and together, like a spoon in a giant bowl of soup,

they stir up the bottom causing the nitrates and phosphates

to come to the surface.

And it's this rich upwelling that really kicks off

Svalbard's phytoplankton bloom.

The meeting of these two currents

holds the key to the unique success of this chilly microworld.

The phytoplankton couldn't bloom at all without the sun

and this far north, the sun couldn't reach into waters

without the Gulf Stream melting the ice.

And there wouldn't be enough fuel to feed it all

without the collision and mixing of the currents.

And without this incredible level of primary production

at the bottom of the food chain, none of the animals

would be able to take the gamble of living here at all.

And so productive is this microworld

that it supports the largest land predator on Earth.

The bears gamble so heavily on this environment

that they've become too specialised to live anywhere else.

They rely on the food web below them and the frozen sea to get at it.

But the bears don't just get by here in Svalbard, they thrive,

and that's because the females can build up enough of a fat reserve

to be able to live under the snow for six months of the year,

eating nothing at all,

and the reason they do this becomes obvious in spring.

As if not eating for half the year wasn't enough,

she has also been using her own body to feed her two new cubs as well.

Now they are ready to face the new challenges

that lie in our boom and bust microworld.

Luckily, while they've been buried,

their favourite meal has been working hard on its fat reserves

and some of these will feed the next generation of bears

continuing to keep our microworld in balance from the top down.

So this web of interconnectivity in our most northern microworld

is all dependent on the tiny primary producers

at the bottom of the food chain that can bounce into life

and make the most of the returning sunlight.

But without the specific set of conditions found in Svalbard,

the primary producers simply couldn't work on the scale they do.

And without them, one of the most productive areas in the world

could not exist.

Svalbard shows us on a massive scale

the fundamental principal of how microworlds work.

It is not only the creatures that live in them that make them tick,

it's also the processes that shape our entire Earth.