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.
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.
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 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.
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.
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.
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!
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
The movie room with seating for plentyBut 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 heavingFor 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 seasThank you...or should I say Obrigado?
João (John) Pedro T. Zielinski
Complutense University of Madrid/Federal University of Santa Catarina
Don't forget to check out our progress as we fill in the sail lines here
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.
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.
All of us on the science team have had our turn being indoctrinated in the "perils" of XBT deployment. In this video, Luke demonstrates the proper technique for launching an XBT.
Prior to boarding the Langseth, my expectations of the food on board were clouded with visions of elementary school cafeteria slop doled out in aluminum trays and eaten with sporks and a side of plastic bag infused with milk. Little did I know that the folks on board take their food quite seriously. The three meals prepared each day are easily the most anticipated events of a crews’ day.
The galley (a.k.a. the kitchen in land dweller speak) is manned by a cook and steward who are responsible for sustaining the morale for the 53 people on board. The mess is regularly stocked with snacks like crackers, raisins, peanuts, dried prunes (yuck!), popcorn, cold cereal, microwave pasta, deli meats and cheeses, an assortment of milks and juices, coffee, tea, ice cream, and “fresh” fruits and vegetables (which will slowly be replaced with canned fruits and vegetables as the days go by). Cookies and pastries are also available at select times during the day if one is lucky enough to get there before they’ve all been consumed.
We made it! According to the 30 minute log, which is one of the duties that we are given while on watch, we sustained up to 40 knot (74 km/hr, 46 mph) winds and ~7m (23 ft) seas for a few hours last night. That said, and aside from a relative lack of sleep, most of us seem to be no worse for wear. We also managed to travel north of our next sail line by almost an entire degree of latitude, which translates to ~111km (69 miles). We have now turned around, and are heading back to the survey area while working on streamer one. We will then re-deploy the air guns, and re-engage the survey in a couple of hours.
Spanish, English, and American motion sickness remedies.
My laptop's ready!
For the last week, we have been enjoying relatively calm seas. Swells rolled in from distant storms, but the local weather was quite enjoyable. Now the storm that pummeled the east coast of the US last week is headed our way. This storm is expected to give us winds up to ~36 knots and ~7-8 m (~21-24 ft) waves! This is too rough for the more vulnerable components of our gear such as the airguns, which are dangling beneath floats behind the ship. Additionally, our data quality suffers when the weather worsens. When the winds pick up to ~25 knots, we’ll pull in some of our gear, and then turn around to face the storm and ride it out. In the meantime, we are preparing by strapping things down in the main lab and stowing loose items that might roll around and fall over once the ship really starts to roll.
Poseidon's Zodiak on the way over to exchange supplies.
A few years ago, it was realised that seismic provides a method of directly observing the mixing processes, as the different water layers have sufficiently different seismic velocity and salinity for reflections to be generated at their boundaries: we have already seen reflections in the water column of our data, probably from boundaries between North Atlantic water and warmer, more saline Mediterranean water. However there have been relatively few studies of these processes using traditional oceanographic and seismic techniques, a deficiency being rectified by the deployment of XBTs at regular intervals during our cruise.
A successful exchange on medium-high seas!!
In addition to deploying ocean bottom seismometers to record our seismic shots, the German research vessel F.S. Poseidon has been carrying out oceanographic measurements, mainly using CTD casts (conductivity-temperature-depth), which provide more information than XBTs. As a result they had several XBTs left over. These they transferred to us this morning: Poseidon came within about 1 km of the Langseth and sent the XBTs over in a small boat. A real bumpy ride!
Today the Poseidon is recovering eight OBH to download the data they recorded and redeploy them elsewhere within the 3-D box. It will be exciting to see the first OBH data! We won't see the rest of the data until the remaining OBS and OBH are recovered in August and September.
Despite being in the same area, here on the Langseth the science party hasn't seen the Poseidon since our first day passing them on the way out to sea from Vigo. However, this may be because we are all busy below deck in the main lab (with no windows) processing data!
Map in the main lab showing planned profiles. The ones we've already completed are in green
*Follow our progress on the "Survey Area" page as we update the sail lines every ~4 days.
Marine reflection seismology involves actively generating soundwaves (rather than waiting for earthquakes as in many other types of seismology). The ideal seismic source is as close to a “spike” as possible. Sound waves from the source travel into the Earth, where they reflect off sedimentary layers as well as hard-rock surfaces. The returning reflections are recorded by over a thousand hydrophones (underwater microphones that gauge pressure changes created by the reflected seismic waves) in the streamers that we have been deploying for the last four days.
The source consists of a series of air guns of varying sizes, which are hung at a depth of 9m (~30 feet) below large inflatable tubes. The tubes are 60m (~200 feet) long and each has 9 active air guns (10 with one to spare). In our case there are two sets of air guns being towed 150m (~500 feet) behind the ship, that alternately fire. To create a strong source that is as spike-like as possible, the guns are carefully arranged and fire almost simultaneously. The air is released from the chamber of the air gun, creating a 3300 cubic inch bubble pulse, which collapses to create the sound waves.
Orientation of the streamer and gun arrays being towed by R/V Langseth.
The red circles indicate the location of the gun arrays.