Frozen Planet's brinicle sequence explained
BBC Natural History Unit producer Kathryn Jeffs reveals the extreme conditions her film-making crew had to endure to capture the bizarre "ice finger of death" - known as a brinicle - under the ice in Antarctica.Research
All shoots begin with research, and inspiration comes from many places… scientific papers, discussions with scientists, images from books or the internet.
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Often it is difficult to pin down the details you need to set up a shoot, especially when locations are remote, and you do not get more remote than below the ice of McMurdo Sound, Antarctica.
We were lucky to be able to draw on the phenomenal experience of the Antarctic dive legends Rob Robbins and Steve Rupp, who helped pin down a focused "wish-list" of stories I hoped to film.
On that list, but with very little expectation of filming them, were some bizarre, beautiful ice formations they called "brinicles".
I had never heard of them and could find no reference to them at all on the internet.
Eventually, I found one scientific paper which described the speedy growth of these strange ice stalactites. Back then I think only a handful of people in the world had even heard of them.Planning the shoot
I needed to turn the ideas into a shot list, so I got together with the underwater filming team, Doug Anderson and Hugh Miller.
Knowing the quality of the filming which we would be expected to deliver on Frozen Planet, the super-steady shots and intimate close-ups, there was a need for real innovation.
We talked about using ratchets and bolts in the ice, and extendable legs to fix the camera and tripod upside-down to the underside of the ice.
It would mean Doug would have to film upside down, but at least he would be able get shots steady enough and close enough to show the tiny, shy ice-fish which cloud around the ice chandeliers.
Knowing the water was perhaps the clearest in the world, we were very excited about being able to film wide vistas below the ice.
In McMurdo Sound, during the end of winter, the water is so clear that it seems the sea floor stretches on forever, dotted with giant sponges, teeming with red starfish and glistening with crystals of ice.
We really wanted to capture that scene. And we also wanted to get intimate portraits of the tiny invertebrates there.
To do this we needed to use a special "probe" lens which allows for close-up shots of tiny animals, but is also wide enough to show where they are. It had, however, never been used with an underwater camera before; we would need to build a special housing for it.
We also knew that life in McMurdo Sound moves very slowly.
The cold temperatures mean that animals have very slow metabolisms and move at a rate that normal cameras would not really show. We would need to take time-lapse cameras under the ice.
Hugh Miller had worked on an underwater time-lapse system in Antarctica before but it had been heavy and the lighting system had not worked as well as it could have.
But he had ideas for a whole new system and had diagrams and designs.On location
After four days of travelling and a final eight-hour journey in a C-17 plane, we finally stepped on to Antarctic ice. With us were 65 bags of kit, amongst which were our newly-built probe lens housing, specially-adapted tripods and various other gadgets and gizmos for filming.
There were also a few crates containing collections of wires, circuit boards, pencil-drawn diagrams and metal cases, as Hugh had not quite completed the build of the time-lapse kit.
Every morning, our day began with loading the gear into a piston bully, essentially a survival pod on tracks, which Doug would drive to the filming location.
As he left, myself and Hugh would dig out our skidoos from under the snow and race over to the site - an hour-long journey.
Out on the ice, dive huts had been placed for us over holes drilled into the ice below, and these tiny boxes became our home for seven weeks.
They protected us from the intense cold and changing conditions, enabling us to spend the entire day out on the ice with the guys able to perform multiple dives.
I had worked up a detailed script and shot-list which I adapted daily, responding to our growing knowledge of the site and allowing us to target particular shots for the sequences I wanted for the film.
This was crucial for making the most of the short amount of time the guys had for each dive, as there was little time for second chances.
We had some big ambitions - especially with regards to the wide shots we wanted to film.
The ice cover meant that natural light was not always strong enough for us to film. We used special underwater lights which Hugh would carry down and hold in place, hovering still in the water, while Doug filmed.
I sometimes think this must have been the one of the most difficult jobs on Frozen Planet.
Hugh had to remain completely still, floating in awkward positions, in the coldest water in the world, holding heavy, metal, underwater lights in place.
Below him, Doug, using the new probe lens, would focus on capturing shots of giant sea spiders and isopods. When they emerged after an hour, they would often be in visible pain from the cold.Under the ice
We were getting some amazing shots of bizarre polar creatures but we were also starting to see how destructive the ice could be. One of the most poignant moments in the film, I think, is the sea urchin getting caught by ice and floating away to frozen oblivion.
Then, after one particular dive, the guys emerged extremely excited. They had filmed some flowing brinicles. Their shots were beautiful but they had had to leave mid-flow as their dive time was up.
A few hours later, when it was safe for them to dive again, they discovered a river of ice had formed on the bottom of the sea floor. Starfish, urchins and sea snails were caught in the ice - and were all dead.
The race was now on for Hugh to get the time-lapse kit finished. There was no spare time, so each night, after filming all day, he would retreat to our laboratory to turn his pencil diagrams into working kit.
Hugh completed the build, but we were nervous.
Would it work in the cold? Would the housings leak? Would the delicate links that Hugh had soldered together survive the brutal journey - dragged in a sledge behind our snowmobiles?
We needed to try it out and had the perfect place. The guys had seen the beginnings of a brinicle plume in a very beautiful spot under the ice. It meant diving through a narrow tunnel of ice which opened out into a wider, natural galley. This was the territory of a large male weddell seal.
It took an entire dive for Doug and Hugh to shuttle all of the kit back into the ice galley.
Three underwater tripods, three underwater lighting stands, three cameras, three lights, two control boxes, and countless cables were placed and held down with lead weights, the entire operation watched closely by the seal.
The next dive allowed Hugh to test the kit and finally start the time-lapse running. We would need to leave it overnight. Meanwhile the brinicle started to grow.
The next day the guys went down to see whether it had worked. They came up despondent. On arriving at the site they had found the camera face down. Our inquisitive seal had knocked it over. But we had a superb time-lapse of tiny sea floor critters scuttling below. The kit was working.
Another brinicle was beginning. With all the kit in place, the crew could set up quickly. Keeping our fingers crossed that the seal would be less interested this time, we left the kit ticking away, hoping for better results.
That evening we returned and the guys dived again. A stunning brinicle, with its river of ice had formed right in front of the cameras, which stood perfectly poised.
But had we got the shot? The drive back that night was excruciating.
Back at base Hugh finally downloaded the material.
At 0100, exhausted from the day, we watched it for the first time, and it was a pretty emotional moment.
We were now seeing the months of planning, design and many long hours of intricate assembly pay off. The brinicle formation was stunning.
We knew we had captured, for the first time ever, the creation of a rather sinister wonder of nature.Staying alive
We took the safety of this shoot very seriously. We were going to be working under metres of thick ice, in the coldest water in the world - we had to get our plans and the kit exactly right.
We thoroughly researched every part of the kit we used - right down to different glove options. I even organised test dives prior to the shoot to ensure everything was familiar to us.
The kit we used was not only picked for safety considerations but was also key for extending the dive times.
Doug and Hugh had many factors working to restrict their time - not least the limited air in their tanks but also, of course, the extremely low temperatures.
Diving at -2C sucks heat away from the body fast, but by using heated vests, chemical heating pads and wrist cuffs, the crew were able to keep warmer for longer.
Part of our dive routine was to pour near-boiling water into Doug and Hugh's gloves minutes before the dive. These vital tricks of the trade meant warmth, and that meant better concentration, a longer time for filming and happier cameramen.The sound of ice
One of the most striking things, when you dive under the ice is just how noisy it is down there. Sounds travels very quickly and over great distances under water, and ice is a fantastic instrument.
As its grows, moves, melts and breaks, it creates an almost impossible repertoire of sounds.
A deeply resonating hum will form a tonal base, while creaks and groans, strange fizzing sounds, crackles and pops seem to give broken rhythm.
Then the siren-song of a weddell seal begins. Eerie and alien-sounding, it is stranger and more beautiful than any effect created for a science fiction film.
The problem though, is that you cannot record sound on time-lapse cameras.
Also, while diving to film underwater, the bubbles from your own kit are very noisy so, unless there is a diver in the picture, we do not record the sounds during filming.
Instead we make our sound recordings after or before the dives by dropping hydrophones down the dive holes into the water.
Tim Owens, sound editor for Frozen Planet, was able to draw on some beautiful recordings that we and renowned sound recordist, Chris Watson made during our time at McMurdo.