Tag Archives: Celtic Sea

A room without a view……

By Elke Hanenkamp (MSCL Operator)

Enter my lair

Enter my lair

Six o’clock in the morning on board the RRS James Cook somewhere on the edge of Malin Sea in 1500m of water, and my shift as the MSCL operator starts right now. The dayshift (midday to midnight) is still fast asleep and the nightshift (midnight to midday) scientists are eagerly (or maybe more fatalistically) awaiting my arrival. The beginning of my shift marks the start for them that cores can finally be split and described soon (meaning more work for them), therefore I have been jokingly nicknamed “the harbinger of cores”.

My role during this expedition is to collect physical properties data (density, porosity etc) from the vibro and piston cores before they are split on board. I am operating a Geotek Multi-Sensor Core Logger (MSCL) in a containerised lab (also known as “the container cave”, I am in there all the time holed up with the cores). So the obvious question is – what is happening behind the closed door of the container? After the cores come aboard, they are cut into sections and labelled, and then stored for at least 6 hours inside the container to equilibrate to ambient temperature. Only after this period, the cores will be measured on the MSCL, because some of the sensors are temperature sensitive. It is not possible to prop the door open during the measurements, fluctuations in temperature would influence the data. That’s why I am holed up in the container most of the time, every so often delivering already measured cores to the scientists for splitting or taking newly labelled cores into the container.

The Multi Sensor Core Logger is a quite versatile core measurement system, equipped with four sensors – Gamma Density, P-Wave Velocity, Non-Contact Resistivity and Magnetic Susceptibility. While the core is pushed past the stationary sensors, it is scanned, and data from all four sensors is collected at once when the core pauses at a measurement point (in this case every 2 cm). Sequential core sections are loaded on to the logger, this way a complete core can be logged in a continuous process while the data is displayed graphically in real time on the computer. Typically, with measurements being done every 2 cm, a 1 m section can be logged within 15 min, but overall measurement time for one whole core depends on the amount and length of each individual section the core is cut into earlier. The shortest core section we had so far measured only 21 cm. The amount of cores sections measured each day highly varies, but a couple of days ago, 45 sections were measured on the MSCL within my 12 hour-shift, with a total length of a little bit over 41 m (a new record).

This slideshow requires JavaScript.

The MSCL gives us a non-destructive way of analysing cores before they are split and sampled. The measurements can help to characterise the physical nature of the individual cores, e.g. lithology, density, porosity, and will be used in combination with core descriptions and various geochronological data to better understand the timing of ice sheet recession. The high-resolution dataset from the MSCL should also allow us to make correlations between individual core sites in the Celtic, Irish and Malin Seas fringing the North Atlantic.

A view of the world

A view of the world

Sun setting on the Celtic Sea and B-C Transect 4

By James Scourse

A wonderful place.......

A wonderful place…….

The first of the BRITICE-CHRONO marine transects (transect 4, Celtic Sea) was completed late on Saturday evening. It has been hugely successful – the result of unbelievably excellent weather and sea state, detailed planning and effective delivery by a great team. This has been a controversial and enigmatic part of the British-Irish Ice Sheet for decades with generations of Quaternary geologists attempting to reconstruct glacial events from meagre and sporadic sequences. It was the focus of my PhD back in the early 80’s. A lot of this was spent onshore on the Scillies where the evidence suggested that the Late Devensian maximum advance straddled the northern islands – a conclusion that caused me not inconsiderable grief at the time because large and influential parts of the UK Quaternary community could not accept that the last ice sheet reached this far south. Subsequent work with colleagues using new techniques has supported this original interpretation. I also analysed a series of 12 or so BGS vibrocore samples recovered in the 70’s from the central and southwestern Celtic Sea containing “glacigenic” facies. A northern suite resembling the Scilly Till I interpreted as basal till facies, whereas a southern group – containing spectacular microfossil assemblages – appeared to be glacimarine. On the basis of this available evidence I suggested a mid-shelf grounding line and marine terminus to the Irish Sea Ice Stream. I was unable to explain the origin of some apparently “basal” type diamictons very close to the shelf break; they might possibly be iceberg turbates. More recently I suggested – with additional information from palaeotidal simulations – that the huge Celtic Sea linear ridge bedforms are tidal features reworking the sediments of the terminal ice stream and the Channel River.

Then, starting in the late 2000’s, I became aware that Daniel Praeg from Italy and Steve McCarron from Ireland had become interested in these ridges and were suggesting in conference presentations (e.g. INQUA 2011) that the ridges might actually be subglacial “ giant eskerine” bedforms which, if it were true, would mean that the ice sheet reached right to the shelf break. In Daniel’s model the shelf break diamictons are just that – evidence for shelf edge glaciation. One of the original BGS cores – site 44 – recovered till from the flank of a sand ridge which might suggest that the ridges at least partly pre-dated the glacial event; Daniel, following Pantin & Evans (1984) suggested that the ridges have a carapace of glacigenic sediment and were therefore overridden by ice. But, alternatively, do the glacigenic sediments dive through and under the ridges? A major unanswered question was/is the stratigraphic relationship of the glacigenic sediments to the ridges. There was something faintly ironic in all this: I’d had a lot of grief having argued for an advanced southerly position for the ice sheet, and now here was another team arguing for an even more spectacularly extended southerly limit.

Daniel, with great persistence and motivation, has organised a series of geophysical and coring campaigns with Italian, Irish and BGS colleagues – the last in February-March this year – to attempt to resolve the two models. Spectacularly their last cruise recovered overconsolidated diamicton and normally consolidated glacimarine sediments close to the shelf edge at the southern end of Cockburn Bank (for further details). I won’t steal their thunder because their work is being prepared for publication, but it is fascinating and has injected energy into our researches in this area. Daniel and Steve and colleagues Dayton Dove and my former research student Gill Scott, are now working alongside BRITICE-CHRONO colleagues to help address these questions. Having Daniel as a participant on this James Cook cruise has been a delight and the two hypotheses have been constructively batted to and fro, day and night, with lots of jocular repartee on the nature of things emerging on the sub-bottom profiler; “that’s clearly a buried drumlin”, “no, it’s a proto tidal sand ridge” etc etc.! Were that all scientific controversies were discussed in such a friendly, stimulating and constructive way.

This slideshow requires JavaScript.

So, what have we found? Searching for glacigenic sediments in this area is like looking for a needle in a haystick, so aggressive was the subsequent transgressive episode. Much of the sedimentary evidence has simply been eroded (incorporated into sand ridges??!) or buried. The BGS only found glacigenic sediments in 12 cores of the hundreds that were taken. Well, about a third of all our coring deployments recovered glacial or glacimarine sediments, from sites extending from the shelf edge to the Celtic Deep, a total of 14 vibrocores and 5 piston cores. This success is a testament to painstaking preparation – including a reconnaissance geophysical cruise – led by Katrien Van Landeghem, Sara Benetti, Lou Callard and colleagues – so that our targets were well defined. Excellent onboard sub-bottom data has also been crucial, pored over night and day by Daniel, Katrien, Colm, Richard and myself, and the expertise of the BGS and NOC coring teams. There is no doubt that these samples and their contextual geophysical data will transform our understanding of the LGM in the Celtic Sea, a topic that continues to fascinate, bemuse and, occasionally, infuriate. One of our key targets, site 44, stubbornly refused to yield anything but sand – dubbed the “sands of woe” by Lou Callard – that left Daniel, head in hands, muttering “Oh bloody, bloody, hell”!

What about the two hypotheses…well, I already have some modified interpretations emerging – new working hypotheses if you like – but I’m not going to be pushed on these until we have the data analysed from the cores. Having said that, I think Daniel might be partly right and partly wrong, and that I, too, might have been partly right and partly wrong. Such is science!

Cruise 1: a perspective from the stern…..

By Jenny Gales and other more reluctant bloggers….

The corer has landed

The corer has landed


The BGS team (Davie, Keith, Mike, Alan, Joe and Jenny) have been busy collecting sediment cores using the BGS remotely operated vibrocorer, with 39 successful cores recovered so far, 14 of which were in the last 24 hours.

The BGS vibrocorer weighs in at 5000kg, in the super-heavyweight class, and can be deployed to a water depth of 2000m. The system consists of a 6 m hollow tube of steel, called a barrel, which is driven into the seafloor by a 1 tonne vibrating pot at the top of the barrel. The whole thing is held in a vertical upright position by a three legged metal frame that keeps it from tipping over on the seabed we hope… Our team, all six of us operate a round-the-clock 24 hour operation, in two shifts of three people, (day-watch Davie, Keith and Alan) and (night-watch Mike, Jenny and Joe) given we occasionally need sleep and time off to read and drink tea.

This slideshow requires JavaScript.

Each deployment of the beast starts with the vibrocorer lying horizontal on the back deck of the ship. First, a hard plastic core liner is put into the barrel. Next, a metal core catcher is added to the end of the plastic liner, to stop sediment falling back out when the core is raised back onto the ship. Finally, a core cutter is attached to the end of the barrel, which cuts through the seafloor. The vibrocorer is then raised up into a vertical position by a BGS winch system and the ship’s A-frame. It’s then lowered over the back deck to the seafloor at about 30 meters per minute. When the vibrocorer lands on the seabed, the corer is started from a purpose built container on the back deck which is fitted with a control and acquisition system. The barrel is driven into the seafloor by the weight filled vibrating pot and collects a core of sediment as it goes down. This usually takes between 15 minutes to 1 hour depending on how hard the sediment is or how persistently nagging the science team are. The materials in the south Celtic Sea have been a little challenging, with coarse sands and other materials proving tough to penetrate. Also the much sought after glacial muds have been tricky to find! Once the coring is finished, the vibrocore is easily (for the most part) extracted from the sea bed and raised back onto the deck of the ship and the now sediment filled barrel is removed. The sediment-filled core liner is taken out of the barrel and is carefully labelled and cut into 1 m sections. The sediment core is now ready to pass on to an expectant science party craving muds……

This slideshow requires JavaScript.

Cruise 1: meet our Marine Mammal Observer

By Marian McGrath
dolph
Hello everyone! It’s been one week since we joined the RRS James Cook in Southampton, even though we didn’t actually leave the port till Friday the 18th due to technical problems with the vibro corer. My role on board is as the Marine Mammal Observer (MMO). The role of the MMO is to ensure the safety and protection of marine mammals from man-made noise pollution in the ocean. This can damage or kill cetaceans which have very sensitive hearing. The Marine Mammal Observer (MMO) is required by law to be aboard any vessel which is carrying out seismic surveys within Irish waters. On this vessel, Sub Bottom Profiler seismic equipment and Multibeam echosounder equipment are being used. In unprotected marine areas an MMO is required to carry out a 30 minute pre Multibeam echo sounder and Sub Bottom Profiler watch followed by a 20 minute watch during the soft start. Sound activity cannot commence until the MMO gives clearance after the 30 minute watch. If marine mammals are spotted within 500m range of the equipment during this watch then a further 30 minute watch is undertaken till marine mammals have left the mitigation zone. If no marine mammals were seen within this time then a soft start would commence. Once the ramp up procedure is started there is no need to stop the equipment during night time hours. The Multibeam and Pinger systems remain active during the survey unless we are on a coring station for longer than an hour in which case they are switched off. They are also turned off during the mid-cruise port call in Killybegs.

This slideshow requires JavaScript.

Marine mammal observations are carried out from the bridge. This gives the best view point of both sides and in front of the vessel. The equipment is always started during daylight hours to allow for MMO watches to be carried out prior to soft starts. Observations are undertaken using a reticular binoculars, a range finder and also by the naked eye. Distance to marine mammals is determined using this reticular binoculars and height above sea level. To determine the range one of the divisions present in the binoculars is placed on the horizon. A formula is then used to determine the distance of the mammal from the ship. The formula is: Distance (m) = (height of eye above sea level (m) x 1000/ no. of mils down from horizon). Throughout the duration of the survey, watches are undertaken throughout the day and any sightings are logged in a computer supplied by The Irish Whale and Dolphin Group. This will feed into a database which is constantly updated regarding location and numbers of various species. Throughout the day recordings are taken of precipitation, sea state, visibility, ship speed, water depth, cloud cover, latitude and longitude, wind speed and direction. So far on this survey Common Dolphins have been seen near the shelf edge of the Celtic Sea. First 4 adult dolphins were seen on the 21st July and later the same day 11 adults and one calf were seen.