Mapping the Galicia Rift off Spain
We are collecting seismic data in the northeast Atlantic Ocean west of Spain to image faults under the seafloor that were involved in continental rifting and breakup and the initial opening of the Atlantic Ocean ~125 million years ago. This rift is notable because very little volcanism appears to have accompanied rifting, as observed in many other rifts worldwide. Instead, continental breakup here appears to have been sufficiently slow and cold that the rocks from the Earth’s mantle were exposed at the seafloor after the crust broke. Previous seismic imaging studies have revealed a continuous sub-horizontal structure that lies at the base of a series of fault blocks beneath the seafloor (called the “S reflector”), and there is significant controversy here and for similar features elsewhere on the role of this feature in accommodating extension and exposing mantle at the seafloor. This program involves collecting and analyzing a suite of geophysical data to image this structure, the overlying fault blocks, the exposed mantle and the sediments in 3D to reconstruct the evolution of the rift. We will collect 3D seismic reflection data to image faults and sediments during a 45-day cruise aboard the R/V Marcus G. Langseth, and three cruises on the F.S. Poseidon to deploy and recover ocean bottom seismometers that will be used to determine the velocity that sound travels through different layers of the earth, which yields information on their compositions.
The Langseth Galicia 3D seismic cruise is winding down. By tomorrow we will be back at the dock in Vigo. Like most seagoing science, we will miss the ship experience, we will miss the new colleagues we have met, we will look forward to getting back on shore, and for many of us the awesome multi-year task of processing, interpreting, and publishing the boatload of data we have acquired.
|This is an example of the data we have collected. Right is to the East and left is to the West. This is a cross section of the Earth about 65 km long. The blue is water. The water depth here is about 5 km. The red and gray colors are a cross section of the rocks below the water. The flat layers are sedimentary rocks. The lumpy bumps (that is a technical term!) consist of blocks of continental crust and of the mantle.|
We thank the Langseth’s Captain and crew for making this possible! These are men and women who live on the sea, and who share their ocean world with us for a month or two. Every now and then, when you can walk 100 meters in a straight line, ask yourself, “Where is the Langseth now, and who is steering the ship, or keeping the engines running, or keeping the deck ship-shape, or providing good food, or every other important task on the ship?” Under your breath say thank you for the experience you had on Langseth.
We thank Robert and his technical team. They worked tirelessly to assemble the 24 km of hydrophone streamer that hears the reflections from the Earth, the 40 or so airguns that make the booms, and all the rigging it takes to tow them spread out behind the ship over 600 meters wide and 7000 meters long. That was just the start. Then they operated the electronic equipment that received the seismic data and recorded it for the scientists. Without them we could not do the science we love.Thank you to the Science Party. We had a total of 20 scientists, including undergraduate students, graduate students, post-docs, researchers, and professors. On Leg 1 we had 14 scientists and on Leg 2 we had 10 scientists. Four scientists weathered both legs. Six joined us for Leg 2. I am very grateful for all your efforts on behalf of the Galicia 3D science. I hope that you learned a lot, had a good time, and met other scientists for the first time. I suspect that we will meet one another many times in the future.I look forward to that!
|This is the Technical team and the Science team for Langseth Leg 2.|
I want to thank the Protected Species Observers for sailing with us. They spent countless hours in the observing tower, high above any other part of the ship. They have sighted hundreds of whales, but most did not come close to the ship. It is windy and cold up there, but their role is important for making sure that collecting our scientific data does not interfere with the creatures who call the ocean home.
Thank you for sending your loved ones off on the Langseth. I can certify that they now know how to do their own laundry and to clean up their cabin before they leave the ship. During the weekly emergency drill, they run quickly up to the muster station on deck and put on safety gear. I recommend that you continue to enforce these behaviors ruthlessly! They will forget them if you let them slack-off. On the other hand, they did not have to cook their own food, or wash and dry their dishes. You will still have to work on these behaviors!
As I write this from the Langseth, we should remember that the Galicia 3D experiment goes on. Our colleagues from GEOMAR and University of Southampton will be on the FS Poseidon from 25 August to 10 September. They will be recovering the 78 Ocean Bottom Seismometers that are still on the bottom (on purpose!). They have been recording approximately 150,000 airgun array shots fired by the Langseth. I know what you are thinking. “How many total recordings of shots are recorded in all the OBS’s?” That would be about 11.7 million shot recordings. This will keep the OBS scientists busy for a while!
I particularly want to thank James Gibson for creating this blog. It has reached out to our friends and to strangers. We plan to keep the blog alive. This project will continue for years.
This week we have been exploring all the parts of the ship we have not yet discovered and were lucky enough to get shown around the engine room and the bridge. It is evident that each area of a ship (bridge, engines, science etc.) has a group of people doing those specific jobs and that the combination of everyone doing their part keeps everything running smoothly; like cogs in a massive machine.
|The engine room control panel. With that many buttons no wonder it takes so much training to work in the engine room!|
The engine room is located in the hull of the ship and is the biggest room on board by far, taking up about 2/3rds of the bottom deck. This is obviously a very important part of the ship because without it we would not be moving anywhere! The Langseth has 2 engines leading to 2 propellers and also 1 bow-thruster. There are so many different bits of machinery down there that it can take 4 years of studying to be qualified to work in the engine room. It is very loud and warm but surprisingly clean and tidy. There are also 2 compressors which are used to pressurise the air for the air guns that we tow.
|One of the very noisy compressors. It is hard to portray the size of these in a photo, they are huge!|
The heat from the engines is used to produce all the hot water for the ship and the engine room also has machines for desalinising our water. Fuel usage is constantly monitored and fuel moved between all the many tanks spread around the ship to ensure even weight distribution. Even though we only travel at about 4 knots whilst acquiring data we burn between 5000-6000 Gallons of fuel a day due to the massive load of the equipment we are towing behind us.
|One of the two engines|
The bridge sits at the front of the ship on top of the main living quarters. From here it seems as if practically everything can be controlled. They drive the ship when we are not driving from the main science lab during acquisition, control the speed, can manage the safety aspects including all alarms and watertight doors and keep a look out for anything floating past that might get caught up in our seismic gear (so far buoys and pallets have been sighted). One very important job of the bridge is to communicate with other nearby vessels. Nobody would expect us to be towing 6km of streamers so we have to make sure we let other ships know with enough time to arrange safe passing, therefore avoiding collisions.
|This is the main control panel in the bridge. There are screens for navigation and|
radar as well as all the speed controls. There are two smaller control panels
on the port and starboard sides of the bridge for work that
involves careful maneuvering e.g. picking up OBS's.
The last seismic line is just being finished right now and then we can get ready to begin equipment recovery. It is about 40 hours until we are back on dry land again!
University of Southampton
As we come to the end of our cruise I thought that now would be a good time to talk about the way in which both seismic and multi-beam sonar data are quantified (basically nerd out). In both cases we "bin" the data into grid cells, which are predefined based on the resolution that we expect to achieve given the ideal data density of individual cells within the grid.
|A screen capture from the multi-beam sonar Seafloor Information System (SIS).|
The image on the left shows swath coverage. The image on the right shows an active ping through the water column.
Multi-beam sonar (swath seafloor mapping) data are collected, gridded (binned) to the predefined cell size, and output in two flavors. Bathymetric grids, which are essentially 3D topographic maps, and Backscatter grids, which display the reflectivity of the seafloor. The reflectivity varies due to both incidence angle of the respective beams and the density of the surface (e.g. hard rock, sediment etc). As the ship moves along at a given velocity, the multi-beam sonar sends a "ping" from the transducers (transmitters) to the seafloor and then waits until the receipt of the last return to ping again. The ping rate (Hz or 1/seconds) is a function of the depth of the ocean as well as the sound speed through water (XBT's are useful!). The swath width also scales as a function of depth. Our average depth is ~4800m (2.98 miles), which allows for an achievable swath width of ~20km (12.43 miles!).
In order to gain insight on the density of the multi-channel seismic (MCS) data that we are collecting we use the Spectra software package. Spectra tracks the position of the ship, streamers, and air guns in real time using GPS and an acoustic network, and then bins the data accordingly within the predefined grid. The goal is to get an equal amount of seismic traces (reflected seismic waves) in each bin. The traces can then be stacked (combined), which increases the signal to noise ratio. Stacked traces within a bin are called "fold" and ideally represent traces from all offsets along the streamer in respect to the source.
|Swath coverage display of the backscatter (reflectivity of the seafloor) collected across a swath.|
|A screen capture of the Spectra display. The image on the left shows active binning of the MCS data.|
The image on the right shows the bins being infilled (filling holes).
We are getting to the end of the "No Mores," which means we are finished on Friday!! Stay tuned for a word from our Chief Scientist along with a look at the MCS data (and our cruise pic).
After all these posts about how we live and work onboard the R/V Langseth you may just be wondering what sort of sustenance keeps us going during the long hours. Well you’re in luck! The excellent cooks serve meals with a smile promptly three times a day at 7:20 am, 11:30 am, and 5:30 pm. Breakfasts always include mountains of eggs, bacon, sausages, and pancakes and on special occasions scrumptious muffins. Lunch usually comes with toasty grilled sandwiches, soup that warms your limbs, and crunchy French fries. Dinner varies but commonly consists of a juicy steak or pork chop, rice, mashed potatoes that put even your Mom’s Thanksgiving potatoes to shame, and a delicious desert like cherry pie. The salad bar is open 24 hours a day and even this far into the cruise still contains crisp spinach, olives, tomatoes, and a variety of other vegetables.
|A sampling of the meals served onboard with cooked by the always smiling galley staff. |
From left to right breakfast, lunch, and dinner.
In the center image the galley staff made up of June, Hervin, and Brian pose behind a lunch of pizza and soda.
We are now in the home stretch of our cruise, steaming furiously down our final sail lines to complete our 3D grid. Can’t believe there’s only four more dinners until we set foot back on dry land!
I was sent to join this cruise half way through because a lot of the scientific party had to leave and nobody more qualified than me could be found at such short notice! I have never been on a cruise before and had no idea what to expect, or any idea how complex and time consuming 3D seismic acquisition is. I have learnt so much about the technical side of acquisition and a little bit about the processing side; however I have also gained a lot of non-scientific tips and tricks! Here are my top 5 tips:
1) ‘Boring science is good science’ – If you are bored on a 6 hour watch that is a good thing because it means that everything is running smoothly and good data is being collected. Having things to do is always a bad sign! Things have been running pretty well recently and as a result I have greatly improved my crossword skills.
2) Things will break, don’t panic! – This is a hand me down ship filled with second-hand instruments from industry vessels. Because of this a lot of the equipment is temperamental and repeatedly needs to be fixed. However, I have also seen instruments that have been offline for days randomly start working again so you never know!
3) Duck tape has a million uses – There is no end to the list of things duck tape is used for on this ship: keeping weights in place on streamers, keeping your laptop on the desk during bad weather, taping your ladder to your bunk so it doesn’t bang during rough weather and keeping ropes in place on the deck to name a few. It seems like any problem can be fixed with tape.
|If you don't want your office chair rolling around or you need a cable tie just use tape!|
4) Hoard food – When food you like is put out in the mess then take it while you can. A few days ago a gigantic tub of mini snickers and bounty bars was put out in the mess….I have never seen chocolate disappear so fast!
5) Taking a shower is the most dangerous activity on the ship – I recommend keeping either an elbow or hand on the wall at all times so you can feel when you start to move. I think taking a shower is probably the best form of exercise on the ship because of the amount of effort and energy it takes just to balance. Also, never soap the bottom of your feet in rough seas. That is probably classified as an extreme sport!
University of Southampton
As Natalie told you, the Main Lab operates for 24 hours a day, but we have a 6 hour shift (nobody can work for 24 hours of course!). So, what are we going to do in our free time? That is a great question! Let me show you the Marcus Langseth's free-time facilities.
Located next to the Galley we have our Library which has a lot of good books (I was reading the Che Guevara's travel book before the beginning of this part II, I really want to finish it!) and these excellent chairs...they're really comfortable, believe me. You can also find a variety of mystery, fiction and scientific books on the shelves.
|The library with a wide variety of books|
Yeah, but John actually I'm not a book lover ...
No problem! This is what you need! A 42-inch TV screen and a big collection of movies and TV shows. Ah, and don't forget the PS3, which makes the crew's free-time fun. I have to admit something to you, I've never used the movie room, but maybe sometime I will go there to catch a movie or documentary.
|The movie room with seating for plenty|
But if you're an athletic person, this is your place, the gym!
It's a little bit small, but if you think we're in the middle of the ocean, the luxury of having some equipment must be appreciated.
|The gym ... be careful when the ship is moving!|
So, there is a treadmill, some free weights, etc. Be aware of the pitch, roll and heave! These are the movements made by the ship. Instead of explaining them, I'll post an image which can perfectly illustrate what I'm trying to say.
|The differences between pitching, rolling, and heaving|
For those who appreciate an indoor sport, we also have a ping-pong table. It's located one level below the Galley, at the Main Deck. I didn't use this table either, but I'll launch a challenge: Try to play ping-pong during rough seas! Imagine how cool a ping-pong game is inside a ship facing waves of 5 or 7m (or even higher).
|The ping pong table ... this could get interesting in rough seas|
Thank you...or should I say Obrigado?
João (John) Pedro T. Zielinski
Complutense University of Madrid/Federal University of Santa Catarina
Today marks the final day before we start the infamous "No Mores". No more Saturdays, then no more Sundays, and on and on until it is time for us to set a course towards dry land. With almost two weeks behind us on this second half of the cruise we have only a handful of sail lines left to complete (see figure below). Once we finish the lines we will head back down to the bottom half of our work site to fill in holes; isolated spots where we were unable to collect data due to strong currents or short-lived equipment problems. After that it's back to port where we will wave farewell to the R/V Langseth as it steams towards the waters offshore of Iceland for another scientific adventure.
Don't forget to check out our progress as we fill in the sail lines here
|A panorama view of the main science lab|
We left off last time with a tour of our sleeping quarters thus it seems only appropriate to now walk through the room where we spend most of waking hours; the main science lab. Located one level below the gun deck, the main lab operates 24 hours a day controlling every aspect of data acquisition from monitoring the multichannel streamers and air-gun arrays to building the computers needed to process the terabytes of data that barrel in.
|An up close view of the numerous computer screens in the main lab|
It can safely be said that when acquiring 3D seismic data during which approximately 6.5 terabytes of raw data will be recorded over 43 days you can never have enough computers.
In the main lab, laptops and computers occupy every surface.
Stand-alone computer monitors duck taped onto desks sit next to laptops anchored by bungee cables.
Power cords, Ethernet cables, and USB connections snake across tables in every direction periodically diving down into a dark power outlet. A bank of computer screens approximately 12 monitors wide and 3 monitors tall encircles nearly half of the lab.
These screens (39 in total) act as terminals that allow us to monitor and control a myriad of processes that are summarized in the image below.
Possibly of greatest importance are the terminals dedicated to “driving the ship.”
We aim to always have the four streamers following in perfect straight lines behind the ship however, cross-currents make this is a difficult charge.
Given the length of 6 km (3.7 miles!) and the weight of the streamers, it is akin to a toy boat towing four 23 m (75 ft) fishing lines straight behind it on a windy day. Thus to keep the streamers in the optimum orientation with respect to our acquisition line we continuously nudge the ship north and south while pulling the heads of the streamers with us. All of the steering is done from a combination of three monitors with the use of the software package “Spectra,” which in the simplest sense determines real time data coverage given the location of the air guns and the streamers.
|A labeled view of the bank of computer monitors that dominates the lab|
Of equal importance are monitors that display the health of the four streamers and the two air-gun arrays.
We aim to keep the streamers at a constant depth relative to the air-gun arrays and also at a depth that keeps them protected from passing ship traffic.
In this part of the Atlantic fishing vessels are common and with our gear sitting kilometers behind our ship and 12 m (40 ft) beneath the sea surface one could see how a vessel might not know that it is there.
Therefore, whenever we see an approaching boat we implore them to keep a safe distance away both for the safety of their vessel and for our gear.
|The back of the lab where most of the preprocessing and quality control is done.|
Additionally, we use this bank of terminals to monitor for the presence of critters in the water, the weather and sea conditions, and the health of the EM122 multi-beam. Sitting back from the semi-circle of computers is another set of desks where the we, the students and scientists, stake our claim. Outfitted with no-slip fabric and duck tape, we have covered the back of the room with our computers, which we use for pre-processing and quality control (QC) of the incoming data.
That about covers the main lab, they keep it pretty cold down here for the sake of the computers so I’m headed up to grab another sweatshirt before I get frost bite.
Stay warm out there!
For those of you who have been following our adventure here's a comparison of the sea-state. I know that the few of us who have been out here for both halves definitely appreciate the difference, and for those joining for the second half it looks like smooth seas ahead!
Also, we have now reached 10,000 page views!! So thanks Mom (and everybody else).
|Our home away from home at sunset|
We started our tour of the R/V Langseth almost a month ago with a walk through of the mess hall and now with our return to the high seas are excited to pick back up where we left off. Let’s begin with our sleeping quarters.
As we all know, the most important aspect of real estate is location, location, location and the same can be said for room assignments when at sea. On first glance, you might be tempted to opt for a room on a higher floor accompanied by a nice porthole to allow full view of the spectacular sea outside. However, hold that thought! Remember that the further above sea level you are, the more you will move with each passing wave. What may feel like a peaceful sway down on the lower levels can turn into a ferocious veer strong enough to topple chairs on the top deck. Thus, if you have any inclination that you could succumb to seasickness it is probably best to pass on the picturesque vista and opt instead for a windowless cabin below. Fortunately, for many of the scientists mental struggles over room selection never occurred as cabins had been assigned to us before we walked up the gangway. Most of the students aboard are sleeping in a suite of cabins that share a common living space endearingly termed the “Snake Pit”. The origin of the room’s namesake remains mysterious, perhaps previous groups of students did some sort of battle there? Or fought snakes? Who knows, for now though it represents a comfortable room where many spend their off time reading books from the library or taking short siestas in between work.
|The "Snake Pit" where students read and lounge between shifts|
All of the cabins aboard share similar features such as a set of bunk beds and matching closets. Depending on the individual setup, you might find yourself lucky enough to also have a set of desks and perhaps even a small couch though these furnishings are found mostly in the higher rooms reserved for the principle scientists and the superior ship mates. Given that work continues around the clock on the Langseth, all bunk beds include an individual light for private reading and also black out drapes to both prevent any light from your bed reaching your room mate and conversely any light from your room mate reaching you. Additionally, all rooms come with either adjoining shared or private bathrooms (termed “heads”). Given the combination of rolling waves and slippery tiles, it could easily be said that the heads may be some of the most injury prone rooms aboard. Thus whenever attempting to take a shower, remember to always keep one hand on the hand rail and if the ship starts swaying don’t neglect to hold on tight otherwise you might suddenly find yourself autonomously ejected onto the cold, wet floor.
|Our cozy cabin equipped with bunk beds and closets|I think that about does it for now, dinnertime is just around the corner and I can smell the ahi tuna from here. Buenas Noches!
As Dale said we are back to work!! We have now completed 3 lines of the ~25 that we hope to cover during this second half.
Being at sea again allows me to look back at our extended stay in Vigo
(Galicia). The port city of Vigo is a unique and beautiful place. The summer months are particularly nice as this part of the Atlantic coast is rainy most of the year. Vigo is just about 2hrs north of Porto (Port wine
), which is in Portugal. The proximity to Portugal and the fact that in the past teaching the English language was not stressed within the school system leads to a population that speaks a mixture of Portuguese and Spanish, but not much English. As a result my (poor) Spanish was definitely put to the test as well as my ability to communicate using what are best described as elementary level sketches.
What Vigoites lack in English they make up in hospitality and a relaxed outlook on life. In short, the idea of a "siesta" is not lost on them. While the bars (and there are hundreds if not thousands) are usually open, the restaurants do not open until 8:30 p.m., and generally not at all on Sunday. However, we did manage to find one that is, and it happened to have very good (and cheap) Tapas. Although off the beaten path it quickly became one of our favorites.
|A view down the alley to one of our favorite bar/restaurants.|
Vigo also has some amazing beaches! After what amounted to a 45 minute walk or a 6 Euro (~$8) cab ride from the ship we could either lay a towel down and get some sun or grab a drink at one of the bars that are literally on the sand. I was shocked to say the least in the shear number of people that were at the beach, and it seemed like there were more during the weekdays than the weekends. Must have something to do with the laid back lifestyle (?)
|Playa Samil on a Tuesday.|
The best beach (Rodas) in the world (The Guardian, 2007) can be found on one of three islands about 45 minutes (16 Euro, ~$20) by ferry named Illas Cies
. The archipelago of Cies is also a Spanish National Park. An interesting thing about these islands is that they look like an above sea analog to what we are seeing sub-seafloor in the data. That is to say that they consist of a series of faulted crustal blocks (granite). The style of faulting is termed "Normal
," which means that the hanging wall moved down relative to the foot wall. This type of faulting is indicative of extension and is expected along the length of this margin.
|A view of Cies from Playa Samil with faults indicated by the arrows.|
The part that we had been so patiently waiting for arrived after almost 3 weeks in this unique place. While I will not miss being in port, I am happy to have had the chance to see and experience this part of the world as it truly is a beautiful place.
|Arrival of "La Cabeza" (the head).|
Welcome back to our blog! As of yesterday morning, we are back at sea and shortly we will resume acquiring 3D data. The repairs to the engine were more difficult than originally thought. We had the Rolls Royce engineers with us for the whole time, working with our fine engineers on the ship. You may not know that Rolls Royce makes really big engines like those in the Langseth. They worked to clean out the engine, ordered a number of parts, and the parts gradually arrived in Vigo. The engine was reassembled and tested at the dock. It worked again!
We sailed from Vigo at 0700 on 15 July with a partially new science team. Several people left the ship because they had conflicts with the extended cruise. They were Donna, Tim, Cesar, Mari, Brian, Steve, Luke, Marianne, Miguel, and Toby. Remaining were Dale, James, Raj, and Sarah. We could hardly do with a science team of four, so we recruited six newcomers. They are Natalie Accardo (Lamont), Milena Marjonovic (Lamont), Gaye Bayrakci (Southampton), Joao Pedro Tauscheck Zielinski (Madrid), Tessa Gregory (Southampton), and Katherine Coates (Southampton). We will try to get photos and bios up shortly.
We are deploying the seismic gear now. We have two streamers out and the third almost out. We hope to begin acquisition in the morning.
We are all excited about continuing our cruise and completing the 3D survey.