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Getting to the core issues

Cover story Global warming

Seabed cores extracted from the ice-covered Arctic Ocean might reveal the truth about global warming. Paul Wheeler reports.

The extent of global warming is one of the major global scientific and political issues of our time.

The answer may lie in the seafloor sediments below the Arctic, which is why this summer, an international team of researchers and contractors will spend a gruelling 45 days taking a series of deep seabed cores just a few hundred kilometres from the North Pole.

The study should help to establish whether current climate conditions are within the natural fluctuations of the last 2.5M years or whether the globe really is warming at an unprecedented rate.

Samples will be taken from sites along the 1,800km-long Lomonosov ridge, which extends from north of Greenland towards the coast of Siberia.

This area is interesting not least because it has been geologically stable for at least 50M years, so should provide a continuous profile of seabed deposition unaffected by erosion, but also because the flat-topped Lomonosov ridge is in relatively shallow waters, around 1km deep.

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

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.

And while there is growing excitement among the scientists over what they will be able to do with the cores, the effort right now is making sure this summer's expedition is successful and they actually have samples to work upon.

The main technical challenge is that the Arctic Ocean is covered year-round in several metres of ice that typically moves at a rate of around 100m an hour.

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

Key to its operations is a heavecompensated 200t capacity coring platform, which will be mounted on the Norwegian ice-breaker Vidar Viking.

The Vidar Viking will take up to an estimated 10 days to reach the Lomonosov ridge from Tromso in northern Norway, giving just 25 days to complete coring 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 - from just above freezing to -10degreesC, although they may fall as low as -20degreesC.

To cope with these extremes, Seacore is fitting out 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 send a crew of nine to work the platform - two teams of four and a team leader, who between them will work 50, 12hour shifts.

Seacore has taken on the job in the knowledge that ACEX's attempt is not without precedent - an expedition in 1996 failed to recover core.

During the earlier expedition, undertaken using 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 the ice sheet. Once the drill string is fixed into the seabed, it is very vulnerable to lateral movement.

This time round, ACEX is sending two additional support ships. An as yet unchartered icebreaker will lead the way, cutting a path through the ice sheet; Vidar Viking and trusty Oden, which will be the headquarters for ice management and scientific operations, follow.

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

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

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

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

Another problem is that geologically nobody quite knows what to expect. Seacore will use specialised sampling and coring tools developed by the British Geological Survey that should give a fighting chance of nearfull core recovery, whether Seacore encounters soft sediments or rock.

Pole to Pole

Friends of Seacore's drilling crews may soon stop asking: 'Been anyway interesting recently?'

For Seacore is about to embark on an incredible twelve 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 in August and September is a US-funded 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.

Then in February next year it moves down to the Antarctic, mobilising from Chile, for the 53-day Shaldril programme to core seven boreholes to depths up to 300m in 700m of water.

According to Richards these are three extremely challenging jobs and, given lead-in times of many years, it is incredible that they will run almost back to back.

Picture: Swedish Research Polar Secretariat

Who's who

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 (ESO), a consortium coordinated by British Geological Survey and including the University of Bremen and the European Petrophysical Consortium with the assistance of Swedish Polar Research Secretariat and GFZ Potsdam.

SeaCore is ACEX's coring contractor.

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