Glorious Mud.

We have been coring in the Traenadjupet region, and have seen some fabulous examples of a range of processes recorded in the mud. We are hopeful for some great results from these cores, though this will take some time to work up, but in the meantime, here are a few examples of some of the wonderfully colourful and exciting mud cores we have taken recently:

This layer has been described as the Pistachio Green horizon after its distinctive colour. This was the first core we found it in, though it has appeared in several others. The exact chemistry and mineralogy of the layer will be part of the post cruise work, but this is an unusual colour, and will unfortunately fade over time.

This very unusual deposit looks remarkabaly like a butterfly, but is in fact a series of mud boulders that were caught up in a submarine landslide. The mud would have been partially consolidated at the time, and the layers ripped up and rolled into boulders, which we have then cored through.

This picture is a close up of one of these contorted mud boulders, and shows that the sequences of colours is symmetrical across the pale brown horizon. When interpreted as having symmetry, andthe fact that these layers terminate against the side of the core, we can be sure that they are boulders of mud and not an artefact of the coring process, which can sometimes cause disturbance to the layers, as seen below:

The darker mud visible in the centre of the core is running from top to bottom, and there are very few processes that can produce this type of feature. It could be bioturbation, the traces left behind by burrowing fauna that are infilled by sediment, but in our current location in very deep water, this is too large a burrow to be possible. This is unfortunately a product of suction at the base of the core, which can cause mud from the base to be injected upwards into stratigraphically higher layers. This limits the usefulness of the core, but is normally confined to the lower sections.

The unusual black block in the lower core is a boulder of peat that was caught in the flow. It is surrounded by clasts of mud set in a sandy matrix, typical of the type of deposit left by a large submarine landslide. The peat boulder is spongy and soft, and will be useful for us to determine where the flow originated as it should contain macrofossils and pollen.

This wonderful striped section is from a deep basin core, and each of the layers represents a very distal deposit from the submarine landslide. Cores like this one have the deposits separated by a thin section of hemipelagite: "normal" marine sedimentation whcih contains forams and potentially other material that will allow us to date each event. These long basin records are one of the key objectives of the project, areas that capture a long record will allow us to assess how frequently landslides happen, whilst the cores taken on top of the landslides are helping us to understand what makes some landslides tsunamigenic or not.

This final picture shows some very pretty laminations, couplets of sediment that will be part of our research into sedimentation patterns on the margin. They appear only in certain locations and within small sections of core, and are potentially the result of seasonal/cyclic changes in sediment source or the energy of the current.

Millie

The triggers

68.5^oN 8^oE

Notes: Sun has now not set for three days, although the weather has been overcast for the last two days. Graveyard shift currently leads the daytime shift by 17 to 11 cores, not that we are counting. Alessandro is pretty poor at darts. There is a storm coming!!!!

Core Puns:

He who dares.....Cores

The Good, the Bad and the Corer

Cora! Cora! Cora!

The Italian Core

Return of the Corer

Cool Coring

The Beauty and the Corer

101 Cores

Core Story

Harry Potter and the Half Sand Core

The Core

Reservoir Cores

One of the purposes of the 2014 Pelagia Cruise is to collect information relating to the triggering of submarine landslides. Many possible triggers for submarine landslides have been identified. These include earthquakes, rapid sedimentation and gas hydrate dissociation. Working out the specific triggering factor behind individual slides is, however, extremely difficult. Which factor has preconditioned the slope to failure? Which factor has triggered the actual slope failure? Today I was covered in 4000 year old mud by certain members of the night shift (Camilla Watts), what the actual reason for this is unclear [Editorial note: it was well deserved]. Was it the fact that I was inanely putting the word core or corer in film and book titles for two hours? Was it because I thought Harry Potter deserved to be kicked in the shin or because I have never watched or am not likely to watch Game of Thrones? Or was it because I have been talking constantly about ball sports for the last year? Or was it that she randomly got bored and decided it was a good idea?

Although a submarine landslide will not be triggered by a poor pun this example indicates the complexity of the question that we are attempting to answer. Many of the submarine landslides around the Norwegian Basin are closely associated with the numerous trough mouth fans which line the continental slope. These features are produced by ice sheets. Glacial ice is a much more effective erosive agent of sediment and bedrock than rivers and is therefore able to deliver extremely large volumes of sediment to the continental margin very quickly. Rapid sediment loading from ice streams (areas of extremely fast flowing ice) is thought to lead to high pore pressures and instabilities which could lead to failure. Similarly dissociation of gas hydrates, an ice like crystalline structure, into their gaseous constituent parts can also generate high pore pressures which could lead to failure of the sediment. Dissociation of gas hydrates can be caused by a number of factors. These include pressure changes related to changes in sea level and temperature changes caused by ocean warming and cooling. Whilst these factors could trigger a submarine landslide, they could equally precondition the slope to fail.

Where rapid deposition of sediment gas hydrate dissociation has generated a slope preconditioned to fail a further trigger may be needed in order to actually achieve failure. In many cases this trigger is an earthquake. Shaking of the sediment can lead to a loss of structure and subsequent failure. Large magnitude earthquakes are currently relatively rare around the margins of the Norwegian basin. However, as we moved out of the last glacial period earthquake magnitudes in this region increased in response to glacial unloading of the crust as the ice sheets retreated. These earthquakes may therefore have represented a common trigger for many events. Despite the increase in magnitude of earthquakes associated with crustal rebound, not all earthquakes will cause slope failure to occur. Some might even lead to a strengthening of the sediment and reduced likelihood of slope failure.

I hope from this post that it is clear that isolating an individual trigger for large submarine landslides is extremely difficult and presents one of the main questions to be addressed as part of the landslide tsunami project. Only with precise dating of the landslides will we increase the possibility of linking landslides to individual triggering mechanisms, although this may in fact be impossible. Who knows?

Ed Pope

 

A-Level Science and Geography Post

As part of some outreach in June, the cruise team took part in a visit day from a Somerset sixth form college, Richard Huish, who came to the National Oceanography Centre for a series of talks about our on-going research. As part of their visit day, they had a lecture from Dr. James Hunt on the history of landslides from the Canaries, and a visit to the core store (BOSCORF) to see several cores and get an overview of how we interpret landslide deposits. This post is aimed specifically at students during their A-Levels, and hopes to explain the science we are working on within the context of the A-Level syllabus. If you are taking your A-Levels at the moment, please take part in our Q and A on the “Chat to the Team” post; we would love to hear from you!

Part of the A-Level geography syllabus covers tsunamis as a hazard in addition to climatic hazards that affect the UK. Though most case studies focus on the recent earthquake induced events in Indonesia and Japan, though it is worth remembering, that over the Holocene (the most recent geological time period spanning 12000 years ago to present), several landslides have occurred on European continental margins that had the potential to generate tsunamis that would affect the UK. The Arctic Landslide Tsunami Project is playing a key role in working out how much of a hazard submarine landslides pose, and when or if they are likely to occur.  

Shot of dawn from the Pelagia while winching back the CTD (Conductivity, Temperature Depth: measures the characteristics of the water column)

One of the biggest research questions of the Arctic Landslide Tsunami Project, is to assess the link between when these landslides occur, and the climate at the time. This is largely driven by one of the biggest coincidences in timing between two events that occurred approximately 8200 years ago: the Storegga Landslide, and the 8.2 ka BP cooling event.

The 8.2 event was the last of the major climatic shifts to occur, though there have been several others (the Younger Dryas event is a case study within the Climate module, during which time half of the deglacial warming occurred in year (almost 10-12°), at 8.2 ka, a 5.4-11.7° C drop in temperature over Northern Europe occurred in less than 10 years). The 8.2 event is interesting to climatologists as it occurred during a period of relative warmth and stability. During glacial periods, there are numerous records of rapid and large climate shifts known as Dansgaard-Oeschger cycles, which follow a pattern of slow cooling and rapid warming, but few rapid climate shifts are known from the warmer interglacial periods.

Why this matters, is that we are currently in a warm period, not too different to the conditions just before the 8.2 event, and we need to understand not only what triggered the event, but also, the other hazards that were potentially generated by it. The widely accepted theory for the cause of the 8.2 is that an ice dam that had been holding back a large volume of very cold fresh water, generated by the melting of Laurentide Ice sheet (covering North America during the last glacial) suddenly broke, and released this water into the North Atlantic. The North Atlantic is one of the most important components of the global climate system, as the formation of deep water in the Nordic Seas and to the south of Greenland helps drive the northward flow of warm water held within the Gulf Stream that keeps the UK nice and warm.

The second event, the Storegga Landslide, is the largest known and dated submarine landslide in the North Atlantic, and has been placed at 8.15 ka BP. Though this is a hard date to refine, it falls exactly within the coldest period of time recorded in the Greenland Ice records (8.16 ka BP). The landslide generated a tsunami that was 10 m high when it reached Scotland and the Shetland Islands (comparable in height to the two recent tsunamis), and tsunami deposits have been found along the Norwegian coast and as far afield as Greenland. The landslide itself moved enough sediment to cover all of Scotland in a 100 m thick layer, and an event of this size today would cause significant damage to UK industry and infrastructure, and represent a significant risk to the large oil and gas operations in the North Sea (The headwall of the Storegga Slide is very close to one of the largest complexes: the Ormen Lange field, which was subject to a comprehensive assessment of stability and landslide frequency in 2005 before operations began).

Landslide events are recorded as turbidites, distinctly different layers of silt or fine sand in an otherwise muddy (hemipelagite) background, by looking at the nature of the material in the turbidites, its size, chemical composition, how well sorted it is and the structures it shows, we can tell where the landslide came from, how old it is and whether or not it happened in one big slide (likely to generate a tsunami) or in several smaller slides from the same region (less tsunamigenic potential, but still likely to cause a hazard).

The key question for my PhD, is looking at the timings of these two events, in order to determine if there is a relationship between them. Did the cooling cause the landslide, or did the landslide contribute to the cooling? Are landslides caused by rapid changes in the oceans? If so, are we more likely to see one happen with contemporary global warming?

These questions can only be answered by heading to the deepest parts of the Nordic Seas, the Lofoten basin, and to the parts of the ocean floor that sit directly beneath the deep water currents. This current is generated by the sinking of water in the Nordic Seas, where it splits and part heads north along the Voring Plateau margin towards the Barents sea, and part heads south over the Iceland Scotland Ridge, a shallow sill of 800 m water depth where we are hoping to collect a core that records the strength of this current, and any landslide events that occurred over the Holocene.

If you have a question, A-Level student or not, please feel free to join in the live chat next week, and keep an eye on our other social media streams:

Twitter: #ArcticSlides

Pinterest: http://www.pinterest.com/millie0692/arctic-landslide-tsunami-project-pe391-cruise/

Millie

Musings from a boat

Day 2.7

Notes: Spent the last 12 hours asleep. Now acclimatised to the graveyard shift. Watching the sun set and come up is epic but its called the graveyard ship for a reason. Dinner – salmon fillet, mash potato, green beens and magnum ice cream. Hair – poor. Tan – limited to face. Wildlife seen – two whales, dolphin pod, sea birds and Sheltlands. Rowing machine 1 Millie Watts 0 #cruiseproblems.

Thoughts from 60^oN.

Whether we are following quite in the footsteps of the likes of Sir Humprey Gilbert, Robert Peary and James Clark Ross, the landslide tsunami project cruise onboard the R. V. Pelagia nevertheless seems to combine many British traditions. We are following both our tradition of Polar exploration whilst using the most important of British ideals, our ability to muddle through. We have also commandeered a foreign vessel, a very British practice since the 15^th and 16^th Centuries.

Progress has been relatively slow. So far we have spent our time speeding at 10 knots towards the Afen slide. There has a lot of heaving, pitching and rolling; the boat not the scientist trying to sleep who have forgotten their sea sickness medication. The transit past Scotland has been marked by drizzle and rain. We have also found that the motion of the boat adds an extra dimension to our attempts at darts and table football. Using a dial up connection is far more efficient for procrastination than broadband as you have to wait ten minutes for each page to load. Salt which has crystallised on the deck is a distinct problem for GoPro suction cups.

What can we expect in the future. Larger waves. Longer and longer hours of daylight. Small disagreements turning into full blown arguments. Holland vs Germany in the WC final? More erratic blog posts.  

Ed Pope

Pre-Cruise Planning Post

The cruise campaign plans are nearly complete, with meetings tomorrow to finalise coring locations to meet each of the campaign objectives. The map below shows the cores already in BOSCORF (British Ocean Sediment Core Research Facility) in red, key coring locations in green, and potential locations in yellow, though the campaign plan is subject to change with the weather and conditions at each location. These locations have been chosen to target the distal turbidite deposits from the large landslides on the Norwegian margin, many of which still have uncertain dates. The hope is that by heading to the high points within the deepest parts of the basin, we should find a thin turbidite deposit bounded by enough hemi-pelagite ("normal" marine mud) to date these turbidites accurately. One of the challenges this poses, is that deposition in this part of the basin can be as low as 5cm per thousand years, so in addition to looking for material to provide us with radiocarbon dates, we are also hoping to identify several tephra horizons within these cores. 

One of our other key objectives is to obtain several cores that will provide us with a high resolution climatic archive. The Nordic Seas are a key site for deep-water formation, the sinking of cold saline water, which drives the thermohaline circulation system, and as such, high resolution palaeoclimate records from these areas will allow us to refine our understanding of how these very large landslides fit with climate over the Holocene. The largest slide, the Storegga Slide, occurred during the last significant cold period, the 8.2 ka BP event (thousands of years before present), and it is unknown how, or even if, these two events are related to each other. 

The cruise team depart for Texel on the 2nd July, where we will meet the RV Pelagia and the remaining week will be spent gathering equipment, refining the coring plan and ensuring we have all the required background information we need. This includes swath bathymetry data from previous cruises to the region, courtesy of Julian Dowdeswell and Haflidi Haflidason, and TOBI data for the Traenadjupet Slide Scar from Julian. 

If you are interested in how these sediment cores are gathered, please see this short video detailing piston coring: 

Chat to the Team!

We are hoping to take some questions whilst we are at sea, so if you would like to ask us anything about the cruise, what we are doing whilst we are sea, life at sea or the research that will take place when we get back, send us a question using the CoverItLive app below. This will be dependent on the weather and the internet connection, but to send us a question, submit it at any time, you do not need to create an account, and we will answer it when the internet allows! Your question won't appear until we publish it, so please be patient, but we are looking forward to hearing from you!

Live Blog Arctic Landslide Tsunami Project