Page last updated at 09:20 GMT, Wednesday, 2 April 2008 10:20 UK

Drilling into a climate hotspot

By Martin Redfern
BBC Radio Science

Tents (BBC)
High science: On Mount Haddington for the summer drilling season

Scientists from the British Antarctic Survey have just returned from one of the most ambitious projects of the season: to drill an ice core from the top of a mountain high on the Antarctic Peninsula.

"The Peninsula is the fastest warming place in Antarctica and one of the three fastest-warming in the world," explained team leader Dr Robert Mulvaney.

Map (BBC)

"Over the last 50 years, it has probably warmed about 2.5C, which is spectacular," he told Discovery on the BBC World Service.

From the broad 1,630m summit of Mount Haddington, the highest point on James Ross Island near the northern tip of the Antarctic Peninsula, you get a spectacular view.

Far to the west are high ice cliffs, 1,000m high, leading up to the mountains of the mainland peninsula.

Had you been standing there in 1916, you might have seen the remnants of Ernest Shackleton's party drifting past on sea-ice following the loss of HMS Endurance.

The latest vessel to bear that name, which carried us and the scientists, was able to sail right into the channel that separates James Ross Island from the mainland.

Twenty years ago that channel was permanently blocked by ice.

Different views

Fifty kilometres to the south, there used to be the vast Larsen B ice shelf which broke up spectacularly in 2002 over the space of a few weeks.

Extracting core (BBC)
The core records climate conditions over thousands of years

Now, the Wilkins ice shelf on the other side of the peninsula appears to be disintegrating.

All these changes would seem to be signs of global warming, but are they just a recent phenomenon or part of a natural cycle?

There is controversial evidence from sediment cores drilled from where the Larsen B Ice Shelf used to be that suggest it may have broken up previously.

"Marine sediments tell us that an ice shelf break-up happened around 5,000 years ago as well. This core will tell us for certain if it got warmer then, too," Dr Mulvaney said.

It should also tell him about how the great Antarctic ice sheets began to retreat at the end of the last ice age.

Open water (BBC)
Open water: A sight Shackleton would have liked to have seen

"I have drilled two cores in the region; this one and on Berkner Island, 1,500km to the south," he explained.

"These were both part of the western Antarctic ice sheet in the last ice age, but that retreated rapidly as the ice age came to an end.

"That gives some feeling for how fast the ice sheets can actually retreat. So, it gives clues about how the ice sheet might retreat from other areas if they warm in the future."

To the base

To complete this borehole, helicopters from HMS Endurance had to transport 20 tonnes of supplies and equipment to the mountaintop.

A team of seven scientists lived there in tents for 50 days, working in shifts so that they could continue drilling 16 hours a day.

The main working tent itself had to have a slot in the roof and trench in the floor to accommodate the tall drill, and enable it to swing to the horizontal to extract the ice core.

Ash layer (BBC)
Ash layer: Evidence of past eruptions

At intervals in the ice, there are grey bands of volcanic ash. James Ross Island and some of its neighbours are volcanic, though there is no sign of activity there today.

After some initial bad weather and snow drifting over and even into their tents, the drill team made good progress and, by mid February, had reached a depth of 363m. It was Robert Mulvaney's turn to work the drill.

"I got 20cm into my run (normally you try and drill 1.5m on each run). I got just 22 cm and the drill got stuck. Of course, my colleagues said, you're rubbish at drilling, let me take over," he recalled.

"But we brought the drill back to the surface and we knew straight away that we had got to the bottom. You can't go further than that."

The team managed to drill a small amount of the frozen clay and rock fragments from beneath the ice. This should enable the researchers to date when ice first covered the region.

'Night life'

Completion of core saw a small celebration.

"Next day, two Twin Otter planes took out the ice cores and left empty the ice cave in which we had stored them. So we set it up with Tilly lamps and candles and we sat around on food boxes and partied well into the next night.

"We called it 'The Pit' - the most exclusive nightclub venue in the region," said Dr Mulvaney.

Now, the ice cores are on their way back to the UK for analysis.

Drill (BBC)
When the team pulled out, all its equipment went too

Trapped within the ice are tiny bubbles of ancient air which should reveal atmospheric composition - and in particular carbon dioxide concentrations - well back into the last ice age, possibly 30,000 years ago.

The proportions of different types, or isotopes, of oxygen in the ice should give the team the temperature at the time to an accuracy better than one degree. When the climate is warmer, a greater proportion of the heavier oxygen isotope evaporates from the ocean to leave its signature in the ice.

There are also tiny traces of other chemicals in the ice layers.

The amount of some of them, notably sea salt, should show if there was open sea nearby at the time the layers formed. If there is very little salt, then there were probably extensive ice shelves preventing it getting blown onto the island.

The helicopters from HMS Endurance eventually returned to retrieve the "Antarctic night-clubbers". Everything was shipped out. Nothing but clean white snow drifts across the summit of Mount Haddington.

"When we leave the site, we take everything with us," said Dr Mulvaney.

"We've left nothing in the hole, nothing on the surface. Everything goes out. That's very important to us."

You can listen live to Discovery on the BBC World Service at 1230 GMT on Wednesdays. Follow the link to the website to listen again

The Pit (BBC)
The coolest place in town... if you're an Antarctic driller

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