Tag Archives: Transect 8

End of an Era ……….for the mighty British-Irish Ice sheet and our mammoth fieldwork campaign.

By Chris Clark (with photography by Alex Ingle)

Voyages around a former ice sheet.....

Voyages around a former ice sheet…..

After a decade of dreaming and years of planning our team of 40 data-hungry geoscientists were given the scent and released from their cages (~desks) with the audacious task of blitzing the whole ice sheet to find samples for dating its retreat. This started in November 2012 in a grey drizzle at Seisdon sand and gravel quarry near Stourport and finished 09:30am 1st August 2015 in bright sunshine when we extracted our last sample, a seafloor core, from the Cleaver Bank in the southern North Sea. It really has been an epic two and half years witnessing the Terrestrial Team with sun-cream in the Scilly Isles to shivers in Shetland, and with dressing gowns in Donegal to JCBs in Norfolk. We really did covered the ground from south to north and east to west and snuck in 28 – yes 28 – different islands of Britain and Ireland, including Scilly Rock and Foula. When samples were not easy to spot and grab, we used radar, seismics and some occasional guesses to work out where to dig with shovel or digger or to core the hidden sediments. It is not quite true that no stone was left unturned, but I have been amazed at how close we got to that, thanks to some amazing levels of energy and motivation; it is indeed lucky that our team displayed traits of obsessiveness and kleptomania when it came to sampling. Bloody well done to all.

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So our very last sample (core 179-VC) on BRITICE-CHRONO has now been collected, marking the end of Cruise Two on RRS James Cook. Even though we never got to shout ‘One hundred and …eighty’ it is more than we had planned. We have sailed, steamed, or dieseled 8971.65 kilometres, taking in Skye, Rona, Shetland, and more North Sea banks including (the infamous Dogger) that you could shake a stick at. We have sampled deep (525 m) and very shallow (19 m), and calm and troubled (force 7). Our ship-track might look erratic to some but, as they say in marketing non-speak, it comprises a subtle blend of caution and well-planned targets with a hint of adventure and wild abandon yielding a truly inspiring collection of mud and sand to sate the yearnings of the most inquisitive discerners of ice sheet curios.

The loot under the care of Team Marine (Lou and Margot)

The loot under the care of Team Marine (Lou and Margot)

The haul, now sat in our refrigerated lorry-container and packed in plastic tubes was obtained by lowering our vibro- and piston corers through 18,891.4 metres of seawater and extracting over half a kilometre of sediment (Rich says 542.4 m). As well-known, of course, it is not the length that counts, but the quality. It will be some time however before we know which cores, places and transects yield the best shells and forams for dating, but Margot and Lou have already bagged, sifted and labelled the celebrity shells which we think have the best stories to tell….’well there was this bloomin’ huge great wall of ice that kept crashing down, and would you believe what happened next….’.

Science crew of the RRS James Cook cruise JC123

Science crew of the RRS James Cook cruise JC123

Thanks to Colm and his science team, the Captain and crew and the geological survey coring teams, and the weather, some good planning, crazy hunches and some luck, this scientific cruise has been a great and enjoyable success. We have a mammoth payload that we hope will provide a legacy of new information for decades. It has been a pleasure having Alex, the ever-present black ninja-photographer on-board, – he stalks, clicks and then runs – in his quest to document our highs, lows and silly moments. Hopefully you have already seen much of his work.

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We set out to do 50 years work in five. Taking this cruise with last year’s, which circumnavigated Ireland, along with our >300 person-days of terrestrial fieldwork we have bagged around 15 tonnes of samples for dating and I hope you agree that we have been around a bit. Sorry if we missed your patch, why don’t you have a go? It is an end of an era for our sampling effort. As project leader, I now breathe a large sigh of relief that it is over and has gone so well, phew and phew again. There is a tinge of sadness though, that we all feel as the fun, bonhomie and making of new friends on hard-won field exploits has now ended. No more pie shops or sneaky pints. Team Terrestrial (Rich and his gang) and Colm’s Marine Crew, can now stand-down to great applause. Derek’s Geochron Team have their work cut out to carefully analyse all the samples and then our Transect Leaders (Tom, Dave, Rich, James, Colm, and Sara) will rise to the challenge of making sense of it all and telling us the story that the shell started to blurt out.

Taking things one day at a time

Taking things one day at a time

Chris Clark, signing off on behalf of BRITICE-CHRONO, currently steaming 11 knots, homeward bound, over the Tea Kettle Bank of the southern North Sea. All cores logged and packed and the pinging geophysics finally turned off.

A Perfect Core……..

By Margot Saher, Dave Roberts and Rich Chiverrell (Photography by Alex Ingle)

Darkness. A great mass of ice overhead. The eerie rumbling of a large, uncompromising mass, slowly but steadily on the move. Below a thick layer of stiff red sediment, ground off the red bedrock, crushed and churned into a lumpy, sticky blanket of glacial till.

Dark coasts

Dark coasts

What would later be called Cape Wrath was only miles to the south, but there was no cape yet. Just the grinding of slow and unforgiving ice moving north into the North Atlantic. But the times were changing. The sun gained in strength, atmosphere and ocean started to warm and the gigantic ice mass, later to be known as the British-Irish Ice Sheet, was in decline. As its surface melted, more water reached its bed, and it began to slide helplessly over its own sediments. Slowly it thinned, and retreated in the direction of the Scottish mountains with the ocean lapping relentlessly at its edges.

There seemed to be no hope, but the ice sheet made one last bold dash towards the edge of the continental shelf before it faltered. The recently deglaciated seabed and freshly deposited grey ocean sediments were bulldozed and overrun again by ice on the move, and buried once more in a blanket of red till. Linear ridges (moraines) marked the limit of this temporary re-advance. But it was only a death throw; the re-advance didn’t get far. The ice sheet’s days were numbered. The advance stopped, and turned into irreversible retreat.

A geophysical search for the perfect core.......

A geophysical search for the perfect core…….

Against a backdrop of rumbling, calving icebergs, station JC123-048VC slowly became ice free, as the snout of the ice sheet moved back over the site. A cold, shallow sea took its place; first, still close to the snout of the ice sheet, where streams of meltwater rushing into the waiting sea water lay down a blanket of coarse sand. As the ice retreated further, taking the meltwater streams with it, the sea fell silent. Only fine sediments spat out into suspension by the dying ice sheet made it to our site, slowly covering it in a thick, grey blanket.

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The ice sheet sent a final message as the ice margins retreated south towards the land; a message from an iceberg. As it passed, melting, overhead of station JC123-048VC, pebbles slipped from its icy grip. They plummeted into the depths, impacting into the soft fine clay sea bed. As soon as this excitement started it was over, and the pebbles were slowly covered by more of the same grey clay.

With the great weight of the ice gone, the Earth’s crust rose like an ancient giant from its slumbers, pushing the Scottish continental shelf closer to the sea surface. Over time, the waters shallowed, and the seabed currents became stronger. The last vestiges of the glacial seafloor were scoured by contour currents, which deposited the spoils of an energetic coast on the eroded sediment below. Millennia later coarse sand and shell debris formed a layer of several inches thick. And then on Sunday the 12th July 2015 all changed.

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There was an unfamiliar thud, and then the uncanny sensation of a vibrating tube burrowing into the sediment from above. It cut through the sand in a jiffy, passed the pebbles, and into the soft clays. The tube slid through it like a hot knife through butter. No struggle with the coarse sands lain down by meltwater streams either, only slowing on reaching the stiff, red till. It battled its way into it for a meter and a half. Then the friction became too much. The vibrocorer stopped, and then the whole tube, now full of sediment, was pulled back up to the sea surface, and hoisted back up onto the deck of the RRS James Cook, the ship it had come from. Peace returned once again on to the sea floor, at core site VC123-048VC, a few miles north of Cape Wrath, on the northwestern edge of Scotland; a land mass now devoid of ice sheets and glaciers.

The core came on board and was cut into sections, labelled, scanned, and split. Finally, we, the scientists who had planned the project, planned the cruise, sailed all the way from Southampton to Cape Wrath, and waited for the British Geological Survey (BGS) to deliver the core, first laid eyes on the sediment. The story was there: a stiff basal till deposited beneath the ice sheet; fines marking the first incursion of the sea; further glacial till documenting the ice re-advance, meltwater stream sediments deposited in front of the retreating ice margin; the fine clays deposited when the ice began to recede southwards containing drop-stones from the icebergs, and the marine sand of the modern seafloor. That was what we had come for. And this was the 48th core; none of the previous 47 had told the story of the vanishing British ice quite this clearly.

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Hopefully we’ll be getting more cores like this in the coming three weeks of the cruise. We need this story told in every sector of the British-Irish continental shelf. Only then will we have what we set out for: the complete saga of the Last British-Irish Ice Sheet.

Gripped in the jaws of the Minch

By Richard Chiverrell and Tom Bradwell (photography by Alex Ingle)

1292 km, 51 cores, 177m of sediment, not a bad haul

1292 km, 51 cores, 177m of sediment, not a bad haul


We, the science crew of RRS James Cook Cruise JC123, sailed from Southampton Friday 3rd July bound for the last three transects of the NERC funded Consortium Britice-Chrono, our aim is to work out the timing of the last deglaciation of Britain and Ireland. After a quick stop outside the Solent to test the BGS vibrocore we made hast (10 knots) northwards through the North Sea running geophysical surveys for the North Sea sector (Transect 2) as we went, and in the early hours of Monday 6th July we rounded the northern tip of Scotland on schedule for our speedy (19 knots) tide-assisted passage through Pentland Firth between Orkney and the Scottish Mainland onwards to Transect 8 and the delights of the Minch palaeo-Ice Stream extending north from Skye between the Scottish Mainland and the outer Hebrides towards the edge of the continental shelf and the North Atlantic.

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The Minch seaway ~28-25,000 years ago received ice flow from the major fjords in NW Scotland feeding palaeo-ice stream, which extended north and northwest across the continental shelf. This ice stream dominated the northwestern sector of the British Ice Sheet (BIS). The land- and sea-scape probably developed over multiple glacial episodes, but the sea floor landforms and uppermost geology reflect the most recent deglaciation after 25,000 years ago. The aim of Britice-Chrono is to work out the timescale for this deglaciation, and this has involved fieldwork on land, dating outwash deposits on the Isles of Lewis, Skye and on mainland, and glacially eroded bedrock and boulders across the region. The offshore phase of this research has occupied us, so far, for the last seven days and nights, and involved surveying the sea floor for the morphology and the sediments using acoustic sounding techniques, but critically sampling the sea floor sediments. We have two coring systems on board, a percussive vibrating corer that can sample down to 6 m below the sea bed penetrating the tough materials laid down beneath and in front of former glaciers, and a gravity powered piston corer capable of sampling up to 18m in softer sediments. Our aim is to find shells in these glacial sediments to radiocarbon date and work out the timing of deglaciation.

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The success of the efforts for both our cruises relies on the excellent 24 hour work ethic, diligence and company of the cruise team, science crew, BGS and NOC Piston coring teams and the RRS James Cook captain and crew, all of whom do everything they can to help us. The middle 2-3 days of T8 were particularly nerve-wracking as the BGS crew toiled night and day to fix a particularly truculent problem with the vibrocorer, part of the solution to which lay in finding and removing an electrical break in the 1500 metres of cable that winches the BGS vibrocore to and from the sea bed. Thankfully time was spent obtaining important piston cores in the inner Minch and collecting valuable geophysical data, as the BGS team worked around the clock. As ever in Britice chrono’s experience, the BGS team, had everything needed on board to solve the problem, and cheers greeted the announcement of ready to go, and there followed ‘an in at the deep end’ test of the repair in 500-600 metres of water off the continental shelf fronting the Minch ice stream. Success, with 4.14 metres of glacimarine muds recovered, and on leaving the waters of T8 a further 11 vibrocores were recovered containing the key shell-rich glacimarine and subglacial muds our project requires.
Calm seas, epic sunsets

Calm seas, epic sunsets


Looking back on the Minch experience, it is certainly one of the prettiest (former) ice streams we have worked on during the Britice-Chrono cruises, with land in view and visiting the Inner Hebrides passing the Isles of Skye, Lewis/Harris and Raasay amongst others. The leg has been a considerable success, we have collected 1292.6 km of geophysical data (multi-beam and sub bottom profiler), 51 sediment cores (39 vibrocores, 12 piston cores) and 177.2m in vertical sediment profile; who said the Minch was a small ice stream? Our travels have taken us from Raasay Sound in the south over the edge of the continental shelf at 59° 15’ N, and into near shore waters fronting Cape Wrath and the Summer Isles. The answers to the Britice-Chrono geochronological questions must wait on many months of laboratory analysis, but we leave the Minch with all teething troubles behind us, and a growing bounty of cores in the locker. We are ready for the delights of Shetland…!
A 12m piston core (Tom Bradwell for scale ~ 1.74m)

A 12m piston core (Tom Bradwell for scale ~ 1.74m)

Minching about on a sunny Isle of Lewis

By Rich Chiverrell

Port Skigersta delta

Port Skigersta delta

One of the smaller ice-masses draining the former British-Irish Ice Sheet, the Minch palaeo ice stream drained much of the NW sector of the British–Irish ice sheet (∼15,000 km2) feeding sediments to the large Sula Sgeir fan fronting the continental shelf. But if this is small, standing on the east coast of Lewis (Outer Hebrides) looking across the sunlit, blue seas and skies east to the feeder fjords and mountains of the Summer Isles and Wester Ross helps one visualise how large this former ice sheet really was. Our aim for this ongoing Briticechrono Transect 8 fieldwork was to secure a series of targets for Optically Stimulated Luminescence (OSL) dating from outwash sands from Lewis, one of the outermost land-masses on the western flank of the Minch Ice Stream. This work will support previous sampling efforts targeting boulders on the Scottish Mainland and the Hebrides for cosmogenic nuclide dating. Previous OSL sampling had targeted the inner sector of the Minch on Skye and north of Ullapool. The team (Rich Chiverrell, Matt Burke, OSL Postdocs Rachel Smedley and Alicia Medialdea) set off first thing on Tuesday morning to join Transect Leader (Tom Bradwell) on Lewis. Departing a cloudy Manchester via Glasgow Airport we landed before lunchtime to blue skies, sunshine and searing temperatures at Stornoway Airport.

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Inspired by our surroundings, the weather and the prospect of excellent sediments the four newcomers sped off to meet up with advance team Tom Bradwell, Adrian Hall and Maarten Krabbendam (from the Netherlands) at Port Skigersta in the far north of Lewis. The site an embayment on the western flank of the Minch Ice Stream gave stunning views across the water back to the ice source areas in western Scotland and beautiful turquoise seas. The sediments were very impressive with the sequence a stacked delta sequence with steeply dipping fore-set sands capped by top-set horizontally stratified gravel. Intriguingly the basal delta is buried by laminated bottom-set muds, in turn buried by a second delta fore-set and top-set couplet. The repeating delta suggests changes in water level probably lake level, dammed between the ice stream and bedrock rise into Lewis. We sampled both deltas close to the fore-set – top-set contact. And then for some geological tourism, the raised beach at Galsom guided by Adrian Hall, stunning and confusing sediments, all contributing to produce a plethora of hypotheses. Difficult to address under the banner of Briticechrono, the beach deposits (guess the isotope stage) appear altered by over-ride by ice, locally there is a surface diamicton and the beach pea/rounded gravels are probably thrust or stacked. We have targeted an outwash (ish!) deposit above a glacial diamicton, fingers-crossed for contributing to the debate. Excellent food followed at the Cabarfeidh Hotel our home for the next few days (well some of us!).

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Day 2, still warm, still still (no winds) and the sunshine popped in later! After an epic breakfast (Lewis did us proud) back to the north and just south of the Butt of Lewis the west coast Swainbost Sands offered much promise. The sections were epic more glaciotectonics, tills, shells than you can shake a stick at, and the beach!!!! One of the best beaches I have seen in the British – Irish Isles…. Selecting targets was challenging, much of the outwash deposit was rich with shells, thrust, tectonised and not where it was deposited! How? Well by marginal movements and override by ice and at a substantial scale. Three sample locations were found and in the back, along with crucial in gamma detector comparisons, duplication with different detectors at some of the samples. The sampling completed our targets after ~36 hours on the islands, and so we racked our brains for other targets. After a quick visit ~5/6km south down the west coast of Lewis where we encountered convincing striae in steeply foliated Lewisian gneiss, where the glacial lineation trends cross obliquely the metamorphic structure heading northwest. We also prospected for sites further up-ice around Stornoway; another fine meal at the hotel and some gin-assisted colour-by-numbers approaches to former ice geometry and let’s see what tomorrow brings for our last 3-4 hours on this eye-opening island (hopefully a final sample)….