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Global warming research has led to the Arctic Ocean, where teams of drillers will soon be battling extreme conditions to recover sediment cores from deep below the ice. Paul Wheeler reports.

This summer a team of European researchers and contractors will spend 45 very cold days taking a series of deep seabed cores a few hundred kilometres from the North Pole.

The Arctic Coring Expedition (Acex) involves collaboration between international scientific organisations on a huge scale and is being project managed by the British Geological Survey.

It should help establish whether today's climate conditions are within the natural fluctuation of the last 2.5 million years or whether the world really is warming at an unprecedented rate.

The Arctic Ocean is covered year-round in ice several metres thick that typically moves at a rate of about 100m an hour.

The task of coring in these conditions has fallen to Cornwall-based contractor Seacore, normally known among the civil engineering community for its marine site investigation and offshore foundation engineering activities.

Samples will be taken from sites along the 1,800km long Lomonosov Ridge, extending from north of Greenland towards the coast of Siberia.

The area is interesting partly because it has been geologically stable for at least 50 million years, and should provide a continuous profile of seabed deposition, unaffected by erosion, but also because the flat-topped ridge is in relatively shallow waters, about a kilometre deep.

Scientists hope cores extending up to 480m into the seabed will reveal past climatic conditions at the Arctic, a vital missing piece of evidence in the understanding of historical global climate change and the ability to predict its future.

While there is growing excitement over what scientists will be able to do with the cores, efforts are being focused on making sure this summer's expedition is successful so they have samples to work on.

Seacore's operations revolve around a heavecompensated 200t capacity coring platform, which will be mounted on the Norwegian icebreaker Vidar Viking.

Vidar Viking will take a 10 days to reach the Lomonosov Ridge from Tromso in northern Norway, allowing only 25 days to complete coring of up to five boreholes in water depths of 800m to 1,400m.

The expedition will take place in August and September when temperatures are forecast to be the most favourable. Temperatures should range from a little above freezing to -10infinityC; but may fall as low as -20infinityC.

To cope with these extremes, Seacore is fitting its C200 coring platform with a number of cold temperature modifications.

'At these temperatures the metal becomes brittle and has to be designed and specified to different codes, ' explains Mark Richards, commercial manager of Seacore's exploration division.

The company will also have to prevent its coring and hydraulics systems from freezing and, above all, keep the coring operatives warm.

Seacore will be sending a crew of nine to work the platform - two teams of four and a team leader, who between them will work 50, 12-hour shifts.

Acex's attempt is not without precedent. An expedition in 1996 failed to recover cores and it is hoped lessons learnt from that will enable success this time round.

During the earlier expedition, undertaken from the Swedish research ice-breaker Oden, it was discovered that movements of the ice sheet made it impossible for the coring vessel, operating in isolation, to stay on position.

When the ship was stationary and coring, the ice closed in around it, locking it into the movement of ice sheet. Once the drill string is fixed into the seabed, it is very vulnerable to lateral movement, as this expedition found to its cost.

This time, Acex is sending two support ships to ensure Vidar Viking is not pushed off position. An as yet unchartered ice-breaker will lead the way, cutting a path through the ice sheet for Vidar Viking and trusty Oden, which will be the headquarters for ice management and scientific operations.

Oden will circle Vidar Viking as coring takes place, breaking up the encroaching ice. Dynamic GPS will provide position input to a series of thrusters that will keep Vidar Viking centred above the borehole.

A reconnaissance helicopter will also search out large icebergs and check that none is set for a collision.

Vertical movements from waves and tides are also a risk, which is why Seacore's C200 will be one of the largest and most sophisticated 'heave-compensating' coring platforms ever built. This prevents the drill string snapping as the vessel moves up and down.

Vidar Viking is also being fitted with a 3m ice shield which should prevent small icebergs being deflected below its hull, as these too would shear off the drill string.

Geologically, nobody quite knows what to expect. Seacore will be using specialised sampling and coring tools developed by the British Geological Survey that should give a fighting chance of near-full core recovery, whether in soft sediments or rock.

Seacore is busy commissioning the C200 on the quayside at it Gweek headquarters in Cornwall. While the project is undeniably demanding, the company is unfazed by the task.

Richards says: 'Designing and building specialist bits of kit for one-off applications has been the essence of Seacore's business over the last 20 years; it is just that the challenges have got bigger.'

The drilling crew's journey will not end in the Arctic, because Seacore is about to embark on an incredible 12 months that will see it working from pole to pole via the equator, all in the name of international climate research.

Next stop after the Arctic coring is a USfunded operation in Lake Malawi in equatorial Africa. Here Seacore will mount a C100 drilling frame on a barge to sink four, 500m deep boreholes in 700m of water.

In February 2005 it moves down to the Antarctic for a 53-day programme to core seven boreholes to depths up to 300m in 700m of water.

The team

The Arctic Coring Expedition (Acex) is part of the Integrated Ocean Drilling Program (IODP), which developed out of the Ocean Drilling Programme established in 1985.

IODP includes input from USA and Japan together with Ecord, a consortium of 13 European countries.

Ecord's remit includes obtaining core samples from previously inaccessible parts of the oceans.

Its programme is being realised through the Ecord Science Operator, a consortium co-ordinated by the British Geological Survey, which includes the University of Bremen and the European Petrophysical Consortium with the assistance of the Swedish Polar Research Secretariat and GFZ Potsdam.

SeaCore is Acex's coring contractor.

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