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Episode One: The Great Melt

In the Arctic summer nearly three million miles of sea ice rapidly begin to melt. For the masters of the ice, the polar bears, the change in habitat threatens their survival but for others – like arctic foxes, beluga whales, the elusive narwhals and immense flocks of birds – this brief summer transforms the Arctic into one of the richest places on Earth.

The Nature's Great Events team captures the greatest seasonal change on the planet in a year when the Great Melt was the largest ever recorded – the sea ice had never retreated so far or so fast. In the summer of 2007 a staggering 400,000 square miles of extra ice disappeared. At this rate, many scientists predict that the Arctic summer could be ice-free in 20 to 50 years' time.

As the temperature rises, the cameras follow a mother polar bear and her cub making their first journey on to the sea ice in search of their favourite prey – ringed seals. It's a serious business for the mother but the cub just wants to play. The melt continues and prey becomes scarce.

In Canada's Hudson Bay the bears gather, waiting for the sea to re-freeze. In a dramatic sequence two 400kg males square up to each other to spar. Some of the waiting bears have gone without food for the whole melt and are half their normal weight, losing up to a kilo a day.

Groups of Arctic whales – the elusive narwhals – are filmed for the first time using aerial cameras as they head north to feeding grounds. The whales' journey is risky as they travel along giant cracks in the ice. If the ice were to close above them they could suffocate and drown.

The beluga whales provide one of the most bizarre summer spectacles as hundreds gather in the river shallows to rub themselves on smooth pebbles. This exfoliating action allows them to moult their year-old skin.

Guillemot chicks take their first heart-stopping flights from their precipitous sea cliff nests to the sea – 300 metres below. With the summer so short, they have to return south before the re-freeze. But the chicks' stubby wings are too underdeveloped to fly. To reach the relative safety of the sea they attempt to glide down, with many missing their target. Their loss is a bonus for the hungry Arctic fox family waiting below.

The producer is Justin Anderson.

Nature's Great Events Diary – Quest for Ice Whales

The most challenging character The Great Melt team set out to film was the elusive narwhal – the strange tusked whale that helped inspire the legend of the unicorn.

Each year thousands of these mysterious animals migrate to the north, navigating cracks in the melting ice that act as highways to rich feeding grounds. Just finding the whales in a wilderness of ice in an area larger than Scotland was a huge challenge which involved two teams – one aerial and one diving under the ice.

Director Joe Stevens and cameraman Tom Fitz headed the dive team, travelling from the remote camp onto the melting ice every day looking for signs of whales. The sea ice is a patchwork of shallow melt water pools and raised areas of ice which made the snowmobile journey particularly hazardous.

In order to survive beneath the sea ice in water of two degrees, the dive team had to fill their wetsuit gloves with near-boiling water. Attached to a rope to guide them back, the divers discovered an eerie world of icy canyons lit by shafts of sunlight. With the sea ice dangerously thin, it was a race against time for the teams.

A tantalising glimpse of a narwhal tail breaking the water and the sound of its clicks, recorded with a special underwater microphone, came too late for the divers so the aerial team took up the challenge.

Lead by producer Justin Anderson and cameraman Simon Werry, the aerial team in a helicopter used the information gathered by the divers to locate the narwhals.

Suddenly a narwhal surfaced in a giant crack in the ice, its long spiral tusk breaking the water, and more narwhal followed. Armed with a specialist camera mount, Simon zoomed in on the action and was able to film a sight that even experienced polar scientists had never witnessed.

The incredible detail captured on HD camera revealed the whales travelling through the huge cracks in the ice, using their heads and tusks to widen holes, creating more space to breathe.

Episode Two: The Great Salmon Run

The return of the Pacific salmon every year to the rivers from which they were born is one of the greatest natural events on the planet. More than 500 million salmon travel up to 20,000 miles to return to the exact patch of gravel in the river from which they were born, to spawn and die.

Nature's Great Events travel to the west coast of Canada and Alaska to capture the salmons' return, along with the predators who eagerly await their plentiful prey.

In a TV first, Nature's Great Events film the emergence of a mother grizzly and her cubs from their dens high in the snowy Alaskan mountains. Using a gyro-stabilised aerial camera system, they are able to follow them down a near vertical slope as they make their way to the coast where the fresh new plant life first appears in the spring.

While waiting for the salmon, which are 2,000 miles away, the bears survive by eating clams, barnacles and even grass!

But they face competition from the coastal wolves, which have been known to kill and eat small bears. The team films a dramatic confrontation between hungry wolves and a lone bear. Although effective predators, the wolves find they have met their match.

Using high speed cameras and specially designed digital underwater kit, the crew are able to record how the salmon swim upstream against powerful torrents.

Filming at 100 times normal speed, they reveal how the salmon are able to leap over waterfalls equivalent to a human jumping over a four storey building.

But despite their monumental struggles, the salmon face a greater challenge up river – dozens of hungry bears. Slow motion shots of the bears reveal their hunting techniques, while the underwater cameras record another TV first to show how they use their ingenuity and some fancy footwork to collect dead salmon from the bottom of deep pools.

After spawning the salmon die, and yet their decaying bodies continue to feed the animals gathered along the rivers, as well as providing nutrients to feed the developing salmon eggs in the river.

Time lapse cameras demonstrate that the dead fish also sustain the forest itself. They release stored nutrients – collected during their life in the sea – to feed the great temperate rainforest of coastal Canada.

The producer is Jeff Turner.

Nature's Great Events Diary – Close Encounters Of A Grizzly Kind

Wildlife cameraman Jeff Turner has spent much of the past 20 years filming grizzly bears in the wilds of Canada and Alaska.

For Nature's Great Events he wanted to observe and film how bears caught salmon underwater in a way that had never been done before.

Before filming began Jeff had a new digital cinema camera adapted to fit inside a specially-built underwater housing. This camera recorded very high quality images directly onto a computer laptop by sending the data down a fibre-optic cable. This would allow Jeff to place the camera in the midst of the fishing bears without disturbing them.

But things never go to plan. The cable proved too irresistible to the bears. One mischievous youngster took a big bite out of it and nearly ended that year's filming!

However, the salmon were not in the shallow water where Jeff had expected them to be. He had to follow the bears to the deep pools where all the fish seemed to be hiding out. He could see the bears were trying to get salmon here but he wasn't sure how they could get them in such deep water – as they just don't like getting their ears wet!

Using the remote underwater camera here continued to be a problem. Because the water was so deep the bears couldn't reach the bottom so some of them took to standing on the camera and knocking it over.

After repeated attempts to keep the camera upright, Jeff needed to try a different approach. He decided to stay in the pool with the fishing bears and follow them around hand-holding the camera on a pole.

In this way he was able to film them collecting dead salmon from the bottom of the pool by using their feet to kick up the dead salmon. The way the bears did this had never been filmed before and provided one of the most memorable sequences in The Great Salmon Run.

In the end it wasn't so much new technology that revealed this interesting behaviour, but Jeff's years of experience and understanding of the grizzly bear that allowed him to get up close and personal.