Arctic methane seepage: since the end of the last glacial period to the present day – a talk to the public at the University of the Third Age (U3A), Flavel Art Center, Dartmouth

My name is Frances Cooke, I am a PhD student and I live in Tromsø. I work within a project called SEAMSTRESS which is affiliated with the CAGE institute at the Arctic University of Norway. CAGE is a centre of excellence for Arctic Gas Hydrate, Environment and Climate. SEAMSTRESS is funded by the Tromsø Research Foundation and the Research Council of Norway. Scientific outreach is an integral part of my work as a PhD student at the university of Tromsø. I am passionate about making science accessible to the public through public engagements like this talk today, so it is a pleasure to be here to give you an insight into what I do living in the Arctic.

Our main goal in CAGE is to study methane release from gas hydrates beneath the Arctic Ocean to understand the potential impacts on marine environments and global climate systems, while SEAMSTRESS investigates the processes controlling methane release at Arctic continental margins. I will show you in this talk how we go about achieving those goals.

First, where does methane come from? In the ocean (broadly speaking) methane comes from two sources. It is either: 1) biologically formed (biotic) – from the decomposition and subsequent burial of organic material, either in the top 10s of metres (biogenic) or 1000s of metres (thermogenic) below the surface. At greater depth we refer to the breakdown of organic matter as ‘thermogenic’ – as the process is thermally driven (temperatures are higher at greater depth) and sourced from hydrocarbons; or 2) formed by geologic processes (abiotic) through magmatic processes.

Gas is buoyant and always wants to move upwards towards the seafloor any way it can, it eventually reaches the surface of the seafloor, where it will escape into the seawater. That is, if it is not consumed by methane eating bacteria or converted back into gas hydrate – to name a few of the processes.

What is gas hydrate anyway? First we need to understand a bit about the gas hydrate stability zone – where does the gas hydrate exist? We can recover gas hydrate samples by core sampling. If we are lucky the core barrel penetrates into mud containing gas hydrate – and this is within the gas hydrate stability zone. It is generally (in my study area) in the upper 200m beneath the seafloor and around 400m above the seafloor into the water column (however in some parts of the world gas hydrate stability zones can be 500 to 600m – this is dependent on geothermal gradients – i.e. how hot sediments are with depth beneath the surface). In this setting temperatures are between 4 and 18 degrees Celsius. You may find it unusual that methane is frozen between these relatively high temperatures, but it can exist in this state because it is under pressure.

Once gas hydrate is recovered – this is what it looks like. Everyone who has recovered methane from a core sample has a go setting it alight. It is extremely satisfying to watch the ice burning slowly away in your hand.

Huge quantities of methane are stored worldwide as gas hydrate over continents in permafrost and over continental margins, and some deep sea areas in marine settings.

I will now take you on a journey, first starting in the Arctic, in Russia – Siberia, and Arctic Canada – Baffin island; then moving across to the Barents sea where I will talk about the early work CAGE undertook in the Barents sea. Then I will move out of the Arctic into the North Sea – a little closer to home (i.e. U.K) – where I will introduce the Tsunami that happened in the stone ages and its surprising connection to methane seepage. I will finish the talk by introducing a little about my PhD, my study area is located in a deep water setting – 1200m in the Fram Strait – between Svalbard and Greenland.

Time in geology is a bit like distance in astronomy – the numbers are so vast that it is difficult to make sense of them.

You are probably wondering what this is? It is just a stack of paper in the geology museum in Tromsø. It is made up of 22,700 sheets of A4 paper depicting the lifespan of the Earth. The final sheet of paper represents modern human existence.

In this talk we will also be focusing on a time period depicted by this last sheet of paper –the last 20,000 years, which geologically speaking is very recent times!

So what happened in the last 20,000 years? At 20,000 years we were coming to the end of the last ice age. During this time the ice was at its greatest extent, afterwards the ice started to melt and retreat. Then modern humans came into existence during a period called the Holocene period.

The Barents Sea methane release – that I will come to – started 12000 years ago and the North Sea submarine slide that caused a Tsunami event, happened around 8,200 years ago.

But first I will talk a little about what is happening today:

You’ve probably all heard about the permafrost melting in Siberia. Huge amounts of methane are expected to be released from permafrost this century because of warming.

Here is a photo of a village called Churapcha. This used to be an old airport runway but now the land looks more like bubble wrap. It is now a useless swampy field and it could eventually become a lake.

What you don’t see are these wedges of ice that form beneath the ground. They make up the permafrost. Each year the crack gets larger and over time the ice wedges become thicker. The black is an active layer that freezes and melts each year, but what is happening today, is that the white parts are also melting, releasing methane gas and causing the ground to subside in this bubble wrap pattern.

Now we move to Baffin Island – in Arctic Canada:

Here on this aerial photo subsidence has already taken place and the subsided land had since filled with water and the holes have become permafrost thaw ponds. The permafrost areas are vast.

The image to the right looks quite similar, but instead of looking down on the lad we are looking down on the seafloor – in the Barents Sea. Sonar data has been used to collect this information. The colour scale is water depth with blue the deepest and red shallow. There are clearly many craters here, some larger than a kilometer in size.

Now we focus entirely on the Barents Sea:

During the ice age the crater area was covered by a thick 2km ice sheet. When the ice sheets melted away, huge blow out craters formed. There was a sudden release (much like a lid being taken off a pressure cooker). The gas that had been trapped beneath the ice suddenly had somewhere to go, and it is still being release today (see flares on the figure).

What is interesting about this study is that we can use the melting of the Barents Sea ice sheet as an analogue for what may happen if the Greenland and west Antarctic ice sheets melt significantly in the future. We know that there are significant amounts of hydrocarbon gasses generated and stored beneath the ice there.

Now I am going to show you a reconstruction of the last ice age. This animated ice map was created by Henry Patton. He is an ice sheet modeler. The interactive graph in the top left shows the decline in ice volume in blue accompanied by an increase in sea level in green (from 20,000 years ago until 8000 years ago).

The animated map shows the Barents Sea ice disappearing 12,000 years ago, and it also shows the last of the ice disappearing from Norway around 8000 years ago.

This leads us nicely onto the next part – where I will speak about the North Sea Tsunami. It may have wiped out the last remaining part of Doggerland (which was Dogger Island) and the people living there!

Now onwards on our journey out of the Arctic and into the North Sea.

In 2006 I read a special report in the Independent newspaper with the title: ‘Tsunami horror hits Britain.’ This was not long after the Boxing day tsunami so it really made me want to read further and find out what this was all about.

The purpose of the article was to catastrophise what would happen in the year 2060 if nothing was done to prevent climate change, but in reality the article is slightly misleading. The methane bubble was not to blame for the catastrophic seabed slide, it was an effect rather than a cause. The cause of the Storegga slide and tsunami – or the trigger (however it is still debated) was an earthquake.

In the last 2.7 million years there have been cycles of cooling every 100,000 years, during these times ice ages took place.

The first cycle shows a deglacial period when there was a high amount of sediment loading (blue) – the blue sediments are deposited very rapidly and as a result are unstable (they haven’t had time to compact). The sediments are weak and act as a sliding plane. The second part of the cycle shows the ice sheet at its maximum extent, weighing down the continental margin. When the ice melts (stage 3) there is no longer a weight on the continental margin, and the land starts to rebound. This is when the earthquakes happen. So the slide was most likely triggered by a strong earthquake in the area and the unstable sediments on the slope then disappeared with the slide 8200 years ago.

So what about today? It is unlikely that another tsunami will happen at the Storegga slide area. Why? Because a new ice age with infilling of glacial sediments on to of marine clays in the slide scar would be needed to create a new unstable situation.

This illustration nicely summarises what happens once the earthquake has destabilized the sediment.  The debris flow slips on the sliding plane (refer to blue sediments in previous slide) – made up of glacial marine muds. Within this layer are gas hydrates that are released, further triggering disability and sediment slip.

Now to the final part of the journey – we move back to the Arctic, into a deep water setting, 1200m beneath the ocean in the Fram Strait. Here I will  introduce my PhD project.

The title of my PhD project is ‘Near surface (upper 300m) characterization of faults and fluid flow systems (i.e. the plumbing system beneath) at Vestnesa Ridge – east Fram Strait.’ My main research question is: ‘Why is gas seeping on the west of the ridge but not on the east?’ My aim: is to ‘Identify fluid (gas) flow features and structures that show sediment displacement across the ridge.’ My method/data used is: Seismic data (We use seismic data which is a sort of remote sensing that acquires images of subsurface features using technology that sends out a signal and records the signal that has echoed back. If you think of a baby scan, this is a similar technique.) My preliminary conclusion: ‘There is a spatial variation in the rate of sediment deposition across the ridge which may impact the density of small fluid flow escape features.’

How do we know what the plumbing system looks like beneath the seafloor? Here we have a seismic line across the sediment drift (Vestnesa Ridge). Beneath this structure, gas has accumulated and it seepage from one half of the structure (the east) – the ‘active’ area. Craters at the surface (aka pockmarks) give us clues about what is happening beneath the seafloor. Displacements (vertical black lines) in the seismic data beneath the coloured seafloor topology map (aka bathymetry) connect the free gas (arrows point to gas accumulation) to the surface of the seafloor.

I am investigating two different mechanisms controlling the gas seepage in the active and inactive part of the ridge. The ‘inactivity’ in the west refers to a drop in high methane seepage activity in the last few thousand years. A different process controls the release of methane in the west to the continued (last 2.7 Million years) high flux activity in the east. The process is referred to as low flux, and is much less studied. My current project focus is to investigate low flux seepage activity at the west of Vestnesa Ridge.

On the left (final slide) is my actual data within an illustration and to the right a conceptual model. Using seismic data I am documenting sediment deformation events that are confined to specific layers where pressure build up preferentially occurs. Gas may not be able to travel upwards because of different layer properties that act as seals. Gas may either travel horizontally in the trapped layers or form gas ‘turbation’ structures. Gas builds up in local pockets, mounds form and cracks form above the mounds. When the mound eventually collapses a crater is formed at the surface and the gas that is trapped locally escapes.

In the west the craters are preserved in clay sediments that are more likely to open under much less pressure. They are buried over time and we can observe them 100s of metres beneath the seafloor, as well as on the seafloor today. This tells us that the same processes have been occurring for millions of years.

We also know that the region is active with earthquakes because of the proximity to the mid-Atlantic ridge. Earthquakes can also facilitate movement of gas and gas escape in sediments that are extremely sensitive to even the smallest pressure perturbations. We can also factor in sediment deformation on account of post glacial adjustment. As a result of all these processes, sediment deformation is highly varied, and distributions of fractures are extremely intricate. The details are sometimes masked by disturbances/noise in the data, however the disturbances often provide clues to fluid movement.

To conclude: Gas hydrate is a frozen, naturally occurring and highly concentrated form of methane. Significant quantities of methane are stored worldwide as gas hydrate over continents in permafrost and over continental margins, in marine sediments where water depth exceeds 300m. The Arctic is a particularly sensitive region to methane release, widespread disappearance of Arctic near-surface permafrost is projected to occur this century because of warming.

Could decomposition of gas hydrates through increase in ocean temperature trigger abrupt climate change? This is debatable, but unlikely, particularly in deep water settings, given the depth of the gas hydrate stability zones. Bottom water temperature variations affect gas hydrates shallower than 1.6m below the seafloor – this is not deep at all! We should be most concerned about the melting of the permafrost and shallow water settings.

Will there be another North Sea tsunami? I consider this unlikely at the Storegga Slide area, at least within our lifetime. The Storegga type event takes place every ca. 100,000 years and is controlled by glacial cycles. However, we can only reanalyse when the next major event happens. Earthquakes can easily generate tsunamis, but you also need large quantities of sediments for a major event to happen.

The entanglement

I started my research career with a major entanglement of a wire into the propeller of R/V Professor Logachev in 2006 and I hope my career will not end as well with an entanglement.

My PhD project started with the participation in a research campaign at the mid-Norwegian margin co-organized by British, French and Russian teams. The aim was to conduct an ocean bottom seismic (OBS) experiment where 30 OBSs needed to be driven down to 730 m with a wire. One of the instruments drifted so much that the wire reached the propeller. That was the end of that instrument. The experiment was surprisingly a success.

We planned an offshore dilatometer experiment on R/V Kronprins Haakon in October 2021. The aim of the experiment was to measure, in-situ, the horizontal stress in the upper 20 m of sediment along the continental and oceanic margin west of Svalbard. What for? To see whether it is true that only vertical stress affects the upper part of the sediment packages deposited along continental margins. The main SEAMSTRESS hypothesis is that the motion of the plates at the mid-ocean ridge axes leads to compression of the entire crust against Svalbard, resulting in cracking of the upper sediment. This may cause shallower earthquakes, favor the release of large amounts of methane and promote submarine land sliding.

I was so exited. We managed to get a tender finished on time to hire the company that would provide the instrumentation for the measurements. I had the ship time, the funding and the instrumentation. It was supposed to be a great, unconventional, high risk high gain cruise. And then things happened…

To make the measurements we had a Cone Penetration Test (CPT) machine on board together with 2 expert engineers and the manager of the company that provided the service. The CPT is a heavy machine but the Captain of the ship had enthusiastically confirmed that the ship had strong winches to deal with such heavy machines: the trawling winches. The company never came back with hesitations or feedback about the type of winches that the captain suggested. To me all sounded like good news. What I didn’t know at that time is that I actually was not being wisely advised neither by the ship crew, experts with wires and winches, nor by the company, experts in deployment of their CPT. Before reaching the bottom at the first site of investigation (890 m), the wires got entangled and the experiment got to an end. Yes, as violent as it sounds. After months of work to get in place such an expensive and ambitious, beyond state of the art offshore experiment, it took only a couple of hours to culminate it with zero data.

The crew tried a few maneuvers but they did not manage to deal with the entangled wires so they cut and the instrument stayed at the bottom until 6 months later, Easter 2022, when we came back with the heroic ROV team to recover it.

I can tell the story now that I feel relieved because the company got back his machine. I would’ve not been able of telling the story before the 14th of April (day when the CPT was back on deck) because I was trapped inside a cloud of stress and anxiety. The company was asking for a random compensation on the lost of the machine. They claimed that the ship was responsible for the deployment, while the ship claimed that the company did not master their instrumentation properly. The responsibility stayed in a limbo and conveniently ended-up on the university (the project administrator). I tell it and I almost cannot believe it: the scientist hires instrumentation and expert operators of such instrumentation and hires the ship and its expert crew. None of the experts advised on the suitability of wires. The wrong wires are used. The experiment fails. The research project pays millions for “0” data and for the lack of professional advice by the experts.

A bit of a crazy thing, isn’t it? If you ask me, the decision on where the responsibility relies should have been taken on a trial. Instead, the project pays the mess and life keeps going without major dramas…

Life is life. At least I know more about wires, winches and legal processes.

Snap shot ROV video: The CPT at the bottom hosting two comfortable cods. The heroes in this story are UiB-Ægir and his pilots.

Text and photo Andreia Plaza-Faverola

In-situ horizontal pressure measurements at seepage sites west of Svalbard

Why gas emissions from the seafloor have stopped thousands of years ago in some areas, while it persists exclusively on the eastern part of the Vestnesa sedimentary ridge? This is the question that drives our scientific objectives in the last research campaign planed under the SEAMSTRESS project.

The answer to this question is likely related to the type of sediment and the disposition of the sediment to fracture. To investigate this further we need to measure sediment properties such as in-situ pore fluid pressures, horizontal stress, shear strength. Conducting these measurements is not so easy because it requires expensive and technically challenging instrumentation. The SEAMSTRESS project assumes the challenge of conducting the geotechnical experiments that are lacking to understand the pressure behavior at deep marine seafloor seepage systems in our favorite Arctic laboratory: The Vestnesa Ridge. These challenging experiments are the core of SEMSTRESS which main objective is to advance knowledge on the pressure (stress) field that controls seafloor methane emissions.

In a collaboration with MSH – Marine Sampling Holland and the Marchetti laboratory we are planning to deploy the Medusa dilatometer designed by the Marchetti Lab to measure in-situ the pressure of the Earth at ease and therefore the horizontal stress. To deploy this instrument offshore there is need for a seafloor (sort of) rig. Our colleagues from MSH joined us onboard with their Geomil’s Manta 200 rig, an instrument designed for conducting cone penetration tests in the soil. Geomil started developing this type of instrumentation in the 30s to help the Netherland overcome a struggle with railway failures due to soft sediment.

Manta is a big machine, heavier than anything that has been deployed so far from R/V Kronprins Haakon. The machine also has a power supply requirement that differs from what the ship can provide. Our mission therefor starts with a few days in the fjord working hard to overcome all the technical challenges to get the machine ready for deployment before sailing offshore.

Photo: The Geomil’s Manta-200 rig for Cone Penetration Test (CPT)  onboard R/V Kronprins Haakon. The MSH team together with the ship crew prepare the winches and solvent challenges with the power supply.

Text and photo: Andreia Plaza-Faverola

Fog, winds, waves and WHALES – our jokers

There is not only the weather variable when we work with geophysics off the Svalbard Archipelago…Fog, winds, waves and whales were our jokers in this expedition.

To recover the ocean bottom seismometers (OBSs) from the ocean floor we need to have good visibility and no waves. The waves are in turn dependent on win (to some extent). When we finally got a window with slow winds and no waves, we got the fog to set inn for long hours. When all the rest was suitable for recovery we got the whales to dance and captivate us.

It has been a great learning experience with lots of training on how to observe, hear and sense our surrounding when we are out in the wild open ocean.

The pictures below give a taste of captivating moments we had during our work with the OBSs this time. Now we are heading slowly home. I look forward to my boys and to share with them some nice stories about the Sea.

 (Photo: Vera Schlindwein) – A party of Finnhval (Finwhales) and Knølhval (horn whale) started, we stopped all the acoustics, contemplated and left…

 

(Photo: Frances Cooke) – Just the fog, the calm sea, the nothing.

The unpredictability factor during a cruise

We have been waiting for an ideal weather window to recover the OBSs. Once released from an iron frame that keeps it at the bottom, the OBS starts rising through the water column at about 1 m/s. When it makes it to the surface it is good to have visibility and no waves, so it is easy to see it. We dare to get one under relatively strong winds and it was a bit of a stress to find it – the wind creates superficial waves where the OBS can hide. The crew found it from the bridge using the binoculars. There was a significant drift and we saw it several hundreds of meters north from the ship. It felt like a big relief when Jan came out to tell they had it on site. They fished it fairly easy and the data looks great.

Our first OBS on deck – it is called a “Lobster”. This is one of 5 OBSs we have at the Department of Geosciences at UiT. The little flying-saucer hanging from a flag pole is the seismometer that records both compressional and shear waves propagating through the oceanfloor. A hydrophone (that only records waves that propagate through water) is placed over the bouy, next to the devise that releases it from the iron weight. 

We decided to keep waiting for the wind to ease down. We started then with the seismic lines. We collected 4 lines and we were ready to continue with the recovery of OBSs when the Captain informed me that we needed to sail to Longyearbyen because our machinery guy injured his hand. A helicopter picked him up and that was quit an impressive operation. Helmer Hanssen doesn’t have a heliport so the helicopter stays in the air while a rescuer descends with a rope to get the injured person from the front deck of the ship – incredibly professional and impressive operation. Feeling respectful of those with that metier…

A roundtrip to Longyearbyen and back after having a replacement “makinist” on-board will take us around 22 hours. Now we are leaving the pretty mountains of Svalbard in the background under a wiggly sky. Tonight we expect to continue with seismics and tomorrow early get on track with the recovery of the OBSs.

But who knows what will happen, there is always that factor that makes our research cruises in the Arctic, unpredictable…

The Mountains of Marineholmane stays in the background with a funny sky

 

Text and photos Andreia Plaza-Faverola

Ocean Bottom Seismic Cruise on R/V Helmer Hanssen – Blog by Frances Cooke

Day 1 – A smooth start

We departed Tromsø on the Helmer Hanssen before our first, of likely many, onboard fish lunches. We were glad of the sea breeze after the unusual Arctic summer heat during the past few days. The seas are calm which is always a relief knowing that your journey north is going to be a smooth one and we found the server machine room the perfect place to cool down! We are in transit returning to Vestnesa Ridge – West Svalbard to recover earthquake data from previously deployed ocean-bottom seismic instruments (OBS). OBS are instruments that contain seismometers and hydrophones that sit on the seafloor, listening and recording vibrations from shallow earthquakes.

Last view of the land: Vannøya (photo: Frances)

Onboard we have two of our colleagues from the Alfred Wegener Institute (Vera and Mechita), three from the Seamstress project (Andreia, Frances and Przemek) and two technical engineers (Stormer and Truls). We are busy setting up the GPS required for the active OBS experiment that will take place at the west of Vestnesa ridge. We have Sunil (in-house expert) present through video call while we are near shore! The setup ensures that we have precision in the timing and positioning of each shot fired during the active experiment.

Stormer and Andreia attach GPS antenna to railing (photo: Frances)

Last year during cruise CAGE20_5 we recovered 7 OBS as part of the Seamstress passive seismic experiment. This experiment took place between July 2019 and August 2020. The OBS instruments in the passive experiment record signals generated by earthquakes or other natural sound waves such as whale calls, instead of being actively generated by airguns. During the same cruise, we deployed 10 more OBS to begin a new experiment at the northern termination of the Knipovich mid-ocean ridge. We are now on our way back to recover them.

Whale Tail – photo opportunity while the sea is still calm!  (photo: Frances)

 

Day 2 – Preparing the instrumentation

Temperatures have dropped and the skies are grey. The bathymetry (map of the seafloor) shows a typical Barents Sea display of iceberg plough marks cut deeply into the seafloor as we cross over the ‘Polar Sonen’ – a blue line displayed on the ship’s navigational map extending from Russia through to Iceland. We are still 1 day and 14 hours away from our OBS recovery site, but we have some tests to do along the way.

Barents Sea real time bathymetry swath with iceberg scours (yellow) (photo: Frances)

Preparation: OBS releasers

We are preparing our OBS releasers for testing at ~1250m water depth, away from the shallow Barents Sea continental shelf. It is important to test the instruments at the same water depth as the OBS site to ensure a comparable pressure. The releasers are the most important part of the OBS to test. If they do not function correctly, the OBS will fail to return to the surface. They are called back using an acoustic device that sends a command through the water to the instrument instructing its release. We will lower the cage with all six releasers (2 from UiT and 5 from AWI) and we will talk to them and wait to see if they talk back. Bergen University were lucky this year to recover their ‘lost’ OBS picked up during the AKMA CAGE cruise in May using a remotely operated vehicle.

Top left: all releasers ready to be deployed (in view Kathi, Kunigunde and Kordula). Emma, Diana, Christine and Wojtek – the easily identifiable instrumentation from the Alfred Wegener Institute. (Photos: Frances)

OBS naming

Five of the releasers have names: Kunigunde, Kathi, Kordula, Kaya and Kim. Vera and Machita inform us that all the parts that make up the OBS (hydrophones, frames, beacon, releaser etc.) have names. The names made for the releasers start with a letter K or L. In the labs at AWI, they have in total ~1000 pieces of equipment to manage, including auxillary parts such as laptops, deck units, and cables. They have 80 OBS equipment groups. Each OBS group is comprised of 10 parts. The serial numbers are so similar that naming the equipment makes it much easier to identify them. I ask how they manage to find names for 800+ OBS parts, and they reply that the names are both male and female, and both German and foreign.  The names are also old fashioned such as Kunigunde. Watching the Denmark-England game last night was possibly as intense as the half hour wait time during the recovery of the OBS – at least for some. Others discussed the names of the players:  Boleslaw – an old-fashioned Polish name. A good reserve name for a Beacon.

Top: The deployment of the releasers cage, bottom: Przymek, Vera and Mechita watching the winch wire go out, waiting for the cage to drop down to 1250m before communication with the releasers begins. (photos: Frances)

While Vera, Mechita and Przymek were preparing the OBS releasers, Truls and Stormer were preparing UiT’s two ‘Digi-birds.’ This is equipment used to control the depth of the cable in the water for seismic operations. The birds are mounted externally on a marine seismic streamer cable. They have acoustic devices that measure actual depth of the cable during operation, through an onboard sensor located in the wing module. Periodic adjustments are made to the angle of the birds wings (or “fins”) to drive the bird (and streamer) back towards the target depth.

Top: Truls and Stormer fix the wings to the birds; bottom: Truls and Stormer attach one of the birds to the streamer cable on deck (Photos: Frances).

 

Day 3 – Adapting to the weather

We are now three days into the cruise and we have to wait another 5 hours, after another fish lunch, until we get to the northern termination of Knipovich ridge. The new weather forecast predicts a wave height of under 2m for our arrival and the winds will drop from Sunday evening. If the wave height is larger than 2m, or if the visibility is poor because of fog, we would have to leave the OBS recovery work for another day.

Truls and Stormer preparing the mini GI airguns for deployment (left), the injector air release increasing internal pressure of the bubble created by the generator (right schematic)

 

While we are waiting to arrive on site, Truls and Stormer prepare the mini GI guns. Final preparations prior to deployment include blowing out the air hose (as the air has to be clean before attaching to the guns), checking the solenoid valves and listening for a click when energizing the firing line, and attaching the gun GPS to the gun float.

An airgun releases a high pressure bubble of air in the water to generate an acoustic pressure wave. The pressure variation in the water as a function of time, caused by the high pressure bubble, is called the airgun signature. Next time you boil a kettle, consider the sounds you can hear of bubbles collapsing. This is what to picture when imagining guns firing under water. Not small explosives, that were used much earlier in marine seismic surveys.

The seismic gun set up requires two mini GI (generator-injector) guns (as pictured). Each mini GI gun is made of two independent airguns that sit within the same casing. The ‘generator’, produces the primary pulse, and the ‘injector’ controls the oscillation of the bubble produced by the generator. The volume of air released by the injector increases the internal pressure of the bubble, and prevents its violent collapse, reducing subsequent oscillations. The bubble oscillations are pressure variations that occur, as the bubble expands and collapses on its way to the surface. These bubble oscillations transmit pressure disturbances outwards into the water. The volume of air released by the injector can act to reshape, reduce or completely remove the bubble oscillations that characterize the airgun signature.

We will begin our shift work at midnight tonight. The plan is to recover one or two OBS, before commencing the seismic work in the early hours of the morning.

Day 4

While the night shift took some rest, we successfully recovered one OBS (no. 10) at the northern termination of Knipovich ridge (NKR). The original plan was to recover two OBS but the visibility was too poor. The breaking waves made the search for the OBS a difficult task!

Clock Drift

‘DIRC’ Clocks in the OBS are temperature sensitive. When the clocks are recovered they need to be synchronized right away before they warm. They are synchronized at the beginning (pre-deployment) and at the end (on recovery). It is known that during the experiment the clocks drift linearly. This clock error is applied automatically which addresses the linear drift problem. However, there is also non linear drift which is a much more time consuming fix (requiring several weeks of processing). Vera tells me that the new manufactured (AWI) seismometers were fitted with clocks that have worse drift than the old seismometer clocks. They are less power consuming but the processing as a result is more time consuming!

The seismic deployment began at midnight, and we were ready to start our first 2D seismic line by 01:30 AM. During the night shift we will complete at least 2 survey lines that will take approximately 3 hours each to shoot (line distances: ~25 km). The sea feels a little rough (2m swell), but by tomorrow evening the wind will drop.

 

Bathymetry map displaying NKR survey area with seismic lines and OBS pick up locations (orange), the red cross marks the retrieved OBS no. 10 (recovered late in the evening on day 3)

We completed four seismic lines, finishing the last line just after 18:00. We had to stop work and recover the seismic instrumentation after an incident onboard required a helicopter rescue. We had planned to start OBS recovery at midnight during the calm weather, but now we will head to Longyearbyen and wait for a replacement crewmember to join us.

A very impressive and quick helicopter rescue operation (photo: Frances)

Day 5

We arrived into Longyearbyen 05:50 on what was a very pleasant morning. We tied up to the wharf in view of the seed vault and joining us were three adult common eider ducks (ærfugl) and their 21 ducklings, together with two adult barnacle geese (Hvitkinngås in Norwegian – ‘white cheek goose’). I had initially thought that the eider ducks were pink-footed geese, until Stormer corrected me. He told me a story about an ærfugl he found on the aft of the Kronprins Håkon. On a cold, stormy November day while on the way to Greenland, Stormer moved a stack of pallets to prepare for coring, and there standing before him was a duck. The duck was standing so still, the first thought that came to mind was “who brings a wooden duck onboard?” He took a step forward to take a closer look, to find that the duck was in fact a real duck. An ærfugl. The crew kept her warm and fed, and released her back into the wild in Tromsø.

 

Two barnacle geese, three common eider ducks and their 21 ducklings (photo: Frances)

It was a quick turnaround, and we left Longyearbyen at 15:00 after our new crewmember joined the ship. The plan is to deploy the seismic at 03:00 on our return back to site, however plans can quickly change and the order of activities is dependent on the weather forecast. We left behind bright skies in Longyearbyen, with a striking display of cirrus and cirrocumulus clouds. After eating match worthy food – chili and nachos, and watching the intense euros finals game, we wait three more hours and hope that the waves will calm for the seismic deployment.

 

Prins Karls Forland in the distance with magnificent cloud formations – originally named Prince Charles’ Foreland after King James’ son in 1612 (photo: Frances).

Day 6

Back to site

We arrived back to site at 02:30 and the weather was less than ideal for seismic. We are limited with what we can do in poor weather, but waiting doing nothing is not a favourable option. We deployed the seismic in a slightly uncomfortable but a ‘safe to deploy’ sea state (winds 12-13 m/s). We started the deployment of the equipment at 04:00 then transited to the start of the survey line starting at 05:30. The line was complete at 08:30 just after our fantastic breakfast of pancake topped with berry jam and maple syrup.

The day shift (Vera, Mechita and Przemek) were up earlier than usual at 06:00, as the plan was to start the recovery of the OBS, but as it was too windy they had to wait until later on in the day. We decided the next best thing was to start a small multibeam survey. We plan to use the multibeam map to compare with the same data acquired in previous years, to see if there is any slump movement recorded in the sediments (pictured). We completed three lines of multibeam before cutting the fourth line short to recover OBS #5, and #6 once we had entered a calmer sea state.

Map of the bathymetry (seafloor topography) in the rainbow coloured depth scale, acquired during the small multibeam survey. Orange filled circles are the locations of OBS #5 and #6.

Recovering OBS #5

I hear Vera on the radio at 20:45 “OBS is rising. It’s at 730 metres” so I go up to the bridge to get ready with Truls and Hans (the Captain) to look for the OBS. Outside on the bridge deck are Andreia, Przemek and Mechita ready and waiting for the OBS to come to the surface. Attached to the side of the OBS is a flashing light and radio beacon that sends out a signal in one of four different frequencies, assigned to each OBS. The radio picks up the signal and makes a beeping sound when the OBS is close and Przemek and Mechita are then able to find the direction of the signal in relation to where they are standing on the ship. As the signal can only be picked up close to the ship, relying on sight is sometimes more reliable, so the more eyes on watch the better!

Andreia and Przemek holding the radio, looking and listening for the OBS once Vera has confirmed that it has reached the surface.

Mechita holding her own radio during the search for the OBS.

Bird commonly sighted, flying around the ship – best photo! (photo: Przemek)

Przemek looking the part! (photo: Frances)

Day 7

If it’s not a strong wind preventing the recovery of the OBS it’s poor visibility. We stopped the recovery of the OBS late in the night due to fog, and deployed the seismic in the early hours, ready to go at 01:30. We repeated a seismic line that was shot in bad weather from the day before. This time the line started with fairly low winds (9m/s) and then the wind picked back up midway through. When the line was completed, we had to recover the seismic to transit to the start of the next line. It is a lot of work taking the seismic equipment in and out, but we are unable to transit between lines at a good speed with the equipment in the water. Time is everything when working at sea.

We (the night shift) were let off bringing the seismic back in for the second time in the night. The day shift took over and completed the second seismic line of the day (Line 5). We managed to recover two OBS before lunch, and another at 16:00. All the OBS recoveries went smoothly, and we were joined by a pod of dolphins at 17:40 during OBS # 3 and large number of puffins, in flight circling around the ship. They are the fastest flying birds I have ever seen at sea. They don’t appear to conserve any energy while flying. They look like they are going somewhere in a hurry, and it is almost impossible (using my compact camera) to get a good picture of them.

It took a little longer than usual to spot OBS # 3. Conditions never seem to be completely perfect for the job! This time the glare on the water made spotting the OBS difficult. Przemek was the only one wearing sunglasses, and was able to strain his eyes to spot the OBS some 300-400 metres away from the ship. What made it even more difficult to spot was that the flag was lying flat against the water, instead of upright.

Between OBS sites 3 and 9 we transited for an hour. This was a good opportunity to eat the freshly prepared doughnuts left in the mess. What a treat!

We successfully recovered OBS # 9, and there were hopes to recover the last OBS left on the sea floor, but the fog returned. The day shift OBS team, were exhausted after such a successful day of OBS recoveries and went straight to bed.

 

Andreia watches out for the (not so obvious) OBS near the ship.

The view of the OBS drifting by, moments before catching it, using a hook thrown out to the line to pull it in.

Mechita and Andreia assist with the winch operation as the OBS lifts out of the water.

Day 8

The fog cleared during the night while the OBS team were in bed, and the sun shone briefly. We continued the multibeam survey, started two days ago, all through the night, until breakfast. We had an English breakfast this morning, eggs and bacon, but no beans. The final OBS was recovered mid-morning and OBS preparation for the active seismic experiment has started.

If it’s not the strong wind or the fog preventing OBS work – it’s the sea ice! We planned a seismic experiment before the start of the cruise, in the west of Vestnesa ridge. Here we will most likely encounter sea ice. We discover today that our proposed location for the OBS sits within the open drift ice. It would be foolish to take the risk and deploy the OBS, while the charts show drift ice nearby. I am told that deploying the OBS in sea ice is no problem, but when the OBS surfaces it could get stuck beneath the ice.

The  Norwegian Meteorological Institute (www.cryo.met.no) provides ice charts and satellite images daily that we can use to monitor the whereabouts and movement of sea ice. The satellite imagery is not affected by cloud cover and can acquire data during the day or night and under all weather conditions.

An ice chart overlaid onto the bathymetry (seafloor map) provides location of drift ice in the Fram Strait. The active seismic planned experiment in the west of Vestnesa ridge is within open ice drift.

The latest satellite image used for mapping of the sea ice (cryo.met.no). The sentinel-1 mission includes a C-band Synthetic Aperture Radar (SAR) sensor that has a resolution down to 5m. Red arrow points to west Vestnesa ridge.

The winds were high in the afternoon, so we continued with multibeam mapping, extending away from our first survey area towards the northwest. Once the ship met the sea ice we decided to abort the multibeam survey, change course and head three hours east to prepare ourselves for the active OBS deployment in an ice free conditions.

For the transit there were fresh wienebrød (Norwegian custard centered pastries). De var gode!

Birds pictured on the sea ice, during the last multibeam survey line, heading northwest, towards the western part of Vestnesa ridge (photo: Frances)

Day 9

We arrived to our new active seismic survey location yesterday late afternoon and started with chirp survey lines closely spaced over a previously interpreted mud diapir and buried glacial meltwater flow. The chirp is also seismic data and classed as ‘single channel.’ It uses a hydrophone array mounted on the hull of the ship, and the transmitted sound is just a ‘ping’ or ‘chirp,’ as opposed to ‘multi-channel’ hydrophones along a seismic streamer, that require a small ‘bang’ from the guns. The frequency is much higher; therefore, with this system we are able to image even finer (decimeter scale) sediment layering near the surface. The chirp typically penetrates ~40 m into the sediment in this area, however the chirp system on this ship penetrates just < 20 m, so we are missing some data deeper down.

This morning 5 OBS were deployed for the active experiment. Two belong to UiT and have a short period frequency range for detecting shallow earthquakes and the remaining three are broadband OBS from AWI that also have long period signals that range deeper.  The OBS team had a rocky start deploying the instruments, with the first OBS bashing into the side of the ship, and needed some repairs.

After completing the chirp survey lines and deploying the OBS, we put out the seismic today at 12.15. We will shoot all 12 crosslines and some ‘inlines’ first, then we will move onto the circlular lines. The acquisition survey design is typically in this way for OBS active experiments, with the feature of interest in the centre of the array. The placement of the OBS is also dependent on the topography of the seafloor. We try to avoid landing them on dipping surfaces and away from depressions. We have begun with the crosslines (NE-SW), and by tomorrow we should have come to the end of the in lines (NW-SE).  The wind has finally dropped and the sea is calm – for now!

3D surface in miliseconds two-way time, using a rainbow colour scale, extracted from 3D seismic volume data, shows a buried glacial feature. The purple line is one of the chirp survey lines that passes south of the feature. The profile of chirp line 3 shows the buried glacial debris.

Day 10

We continued shooting seismic for the active survey experiment. Some inlines were dropped, to make up time so that we would be ready by 16:00 to start the circular lines. The weather conditions remain perfect for seismic, the sea is calm and there is a moderate breeze.

One thing is certain while working at sea; you can never be too confident that things will go to plan! We had planned to recover the OBS tomorrow morning after completion of the seismic lines, however a large number of whales showed up within 500m of the ship. As there were so many whales showing up so close to the vessel, we shut down all our acoustic systems, including the seismic guns. On the bridge they saw plenty of finwhales and Knølhval (horn whale) breaching the surface. The ‘Havforskningsinstitutet’ (Institue for marine research) specify that the Greenland whale and Narwals are species that require the most protection.

The mini GI air guns we use for the seismic are 15 and 30 cu.in. The guns are significantly smaller than conventional seismic guns used in industry. Higher powered guns are used to send signals much deeper into the subsurface. We are only interested in high detail in the near surface sediments (top ~300m).

While on the bridge deck looking out in awe, we spoke about how long we should wait before starting the seismic back up. This depends on the water depth. Whales spend up to 45 minutes beneath the surface in deep (+1000m) water, so we could be waiting an hour before knowing whether the whales are still close by. I worked on a seismic vessel where we had a marine mammal observer onboard. However, she would not observe the whales. Instead, with her own hydrophone, would spend the whole shift with headphones on, listening for whale calls. Relaxing shift?

As time is precious, we decided to move away from the active seismic survey site and move south to Svyatogor ridge to complete some seismic lines for our colleagues not on the cruise – in whale free areas.

Whales as far as the eye can see. (photo: Vera Schlindwein)

 

Day 11

We completed two seismic lines, at Svyatogor ridge in the night and there were no whales in sight. The wind speed was low for the first line and had gradually picked up by the start of the second line. We then recovered the guns and streamer just before breakfast, before heading back to our NKR active seismic site. During the first half of the day, the winds reached up to 18 m/s, which was far too much to redeploy the seismic at NKR, so we waited. There was no whale watching.

When the winds had dropped down to 11m/s, we decided to deploy the seismic and finally finish what we had started two days ago! We are nervously waiting for calm weather windows to appear so that we can get back the OBS. The OBS each have a programmed automatic release time, which is 16:00 tomorrow.

The wind dropped to a gentle breeze, and we swiftly recovered three out of the five OBS. The remaining two OBS from UiT are more difficult to see, and the fog had started to set in. We decided to leave them until the morning.

We shot our final seismic line after taking the break to recover the OBS, and after dinner, planned a water column survey over the NKR active seismic study area. Microbial mats discovered on the seafloor, during a previous cruise, suggest release of methane gas and we might expect bubbles escaping from beneath the water bottom.

Fog and stillness (photo: Frances)

Above: EM302 multibeam water column swath (30 kHz), and below: EK60 echosounder (18 kHz)

The water column survey completed in the early hours of the following morning did not show any acoustic flares in the water column, but we saw plankton scrolling across the screen in the single beam echo sounder (fish finder), and bright spots appearing mostly above 500 metres in the multibeam swath. I suspect that we imaged more fish bladders than gas bubbles!

 

Day 12

This morning we successfully recovered the last two OBS. It was a relief to have them all back onboard! Shortly afterwards, we left Knipovich ridge and started our two day journey back to Tromsø. On the way, we will stop at a study site called Bellsund, we presume named after Bellsund fjord, situated on the west coast of Svalbard. The site is actually much further south from Bellsund. It is opposite the Hornsund fjord. Here we will shoot two final seismic lines for our Italian colleagues.

After half an hour in the fresh sea air, watching the birds flying around the ship, I spotted a feeding frenzy. From a distance, it looks like the water is bubbling. Dolphins surface, one after the other, and dive back down into the water. The birds hover above, waiting for the scraps. After their feed, the dolphins could not resist coming towards the ship to play in the waves beneath the bow.

Dolphins playing beneath the bow of the ship (photo: Frances)

 

 

A new cruise season starts – what will the Ocean Bottom Seismometers (OBS) we left last year tell us?

Planning a cruise this year has obviously not been easy – why should have it? We are all across the planet leaving a difficult time.

But here we are, we got onboard for a 15 days research cruise with the main objective of recovering the OBSs that we deployed last year (se previous posts). We are a compact scientific crew this year: Przemek, Frances, Vera, Mechita and Andreia, with support from our engineers Truls and Stormer (nothing to complain about the gender balance). For the first time in many years I am coming to an OBS/seismic cruise without Stefan and Sunil and the possibility of not managing to get a code or a program running makes me anxious J

We left Tromsø in calm waters with a suffocating temperature of nearly 30 C. Now we are back to Arctic temperatures…We have used the transit to set and test software and equipment. Tomorrow we will be on site by 18:00 to pick up the first (southernmost) OBS from 10 we have in the water at the northern termination of the Knipovich Ridge.

Just a few minutes ago they called us from the bridge to see a bunch of Finn whales and dolphins playing together very close from the ship. The perfect spectacle to continue the transit.

 

Photo: Sailing from Tromsø Onboard R/V Helmer Hanssen in a calm sea at 30 C

Text and photo: Andreia Plaza-Faverola

Rituals after our Arctic expeditions

It has become a habit when we finish an expedition in Longyearbyen to celebrate the hard work with a dinner all together in one of the few restaurants in town, Kroa. A day before reaching the harbor Sunil had already booked our table. This year we were the right number of people and got the Round Table, just like King Arthur’s table. Several hours before our closing dinner we were already in town having some drinks together. We continued with the dinner and finished with a round of emblematic bars in Longyearbyen.

Photo: The group with the feet on the ByKai

I write about this because it caused me a big (good) impression to see a lot of life in the bars and streets of Longyearbyen despite all the unusual rules that we have to follow to continue with our “normal” lives. Longyearbyen is a strange place; the city and the people here are full of energy.

We had a cozy night together and some of us came across the ship crew and could share a bit with them outside work. Rituals mark and create time, they define beginnings and ends in our social cycles, they strengthen social relationships.

Now ready to go back home.

Photo: we finish a cruise and a season. The sun tells us “good bye and see you in a while”…

 

 

Text and photos: Andreia Plaza-Faverola

Into the fjord

For the last 2 days we have been waiting for the arrival of the “bad weather” to stop our activities and to go into the fjord…

Here we are now, enjoying the calm waters at the shadow of “Fuglefjell” in one of the Kongsfjorden branches.

We managed to recover the last 2 piezometers and completed more than 20 heat flow stations right before the arrival of strong winds and big waves. I feel relieved. We have had intense days full of data and full of emotions. Now we just wait here, we play basketball; we get lost into philosophical discussions and sophisticated speculations about the results.

Photo: enjoying the calm BEFORE the storm

 

Text and photo Andreia Plaza-Faverola