End of first cruise -- heading out again in 2013

Written by Karin Sigloch on Sunday, 28 October 2012. Posted in Cruise 2012

26 October 2012

pierre028

The “Marion Dufresne” arrived back in Le Port around 9 a.m. this morning, ending our cruise. Over the past four weeks, we deployed 57 broadband ocean-bottom seismometers along a 15,000 km long track. We also gathered bathymetric, magnetic and gravity data along the way, and on some additional profiles. In October 2013, we will head out again to recover the seismometers and their recorded data from the ocean floor, using the German research vessel “Meteor”.

Our ship doctor Pierre Henry did not have many medical cases to attend to. He spent a lot of time drawing, preferably scenes of daily life on the ship. The example above captures much of the essence of our cruise.

 

A life after the Marion Dufresne?

Written by Maria Tsekhmistrenko on Sunday, 28 October 2012. Posted in Cruise 2012

25 October 2012

The last day has broken. Only a few hours left before we have to leave the ship. For the first time in weeks we are going to feel firm ground under our feet. We are leaving the ship, which was like home for us, though for a relatively short time.

 SAM 2233

Over the past days, I wistfully I enjoyed my coffee on my favorite outlook spot on the deck. I never got bored of the beautiful view of the ocean, and every day I enjoyed it more. While sitting here, I remembered many moments on this ship:

Jeans “plat au fromage”; Patrik, our best friend behind the bar; Chris trying hard to find some people to play baby foot with him after each meal; Henning’s long way down to get his “big, black, bad” – coffee; Karin and Gulihem trying to find the perfect deployment point for the OBS; Sacha’s tireless night shifts, which helped to sit out the long hours; Heiner playing Guitar; Oliver’s daily search for the next seminar speaker; the united march of the officers to the dinner table; the deployments, the Marion Dufresne, the ocean…

Thanks to all of you taking part in the cruise (LEG 1 and 2). Thanks for the unbelievably great, exciting, educational, fascinating and definitely unforgettable time on this ship. 

Deployed and celebrated the last OBS

Written by Karin Sigloch on Sunday, 28 October 2012. Posted in Cruise 2012

23 October 2012

We deployed our 57th and last ocean-bottom seismometer yesterday afternoon. The happy event was celebrated with a small ceremony on the aft deck, immediately before the final launch.

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Special outfit for a special occasion: Christine Läderach and Henning Kirk marching to the rear deck, to check the last OBS and attend a little ceremony prior to its launch. (Photo: Maria Tsekhmistrenko)

RHUM-RUM celebration-1

Cruise leader Guilhem Barruol addressed a numerous audience, who had emerged from all corners of the ship. Then we awarded Grand RHUM-RUM medals to the three boatsmen Arthur, Gilles, Jérôme, and their crews, thanking them for their skillful help and good humor at all times. They have very professionally deployed our instruments around the clock, and rendered many other services on deck. (Photo: Wayne Crawford) 

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The final OBS was launched immediately afterwards by Arthur and his crew. We hope and assume that it and its 56 colleagues are now recording seismic signals on the seafloor until 2013. At this milestone for RHUM-RUM, Satish Singh opened a few bottles of champagne for everybody to enjoy. (Photo: Karin Sigloch) 

RHUMRUM-GroupPhoto

Happy faces at the last OBS launch: scientific party and ship crew of mission MD 192, Leg 2. (Photo: Wayne Crawford)

 

SWIR array deployed

Written by Chris Scheingraber on Wednesday, 17 October 2012. Posted in Cruise 2012

17 October 2012

During a long night for the OBS team and the PI's of this mission, the sub-array of 8 ocean-bottom seismometers was successfully deployed on the Southwest Indian Ridge.

01 SAM 1750

3:30 AM in the science lab.

 

The sub-array of 8+1 instruments that we were deploying last night.

The array of 8+1 instruments that we were deploying last night.

 

As a test for next year, our colleague Wayne had dropped an absolute pressure gauge close to one of the first array stations. After all eight seismometers had been deployed, the pressure gauge was called back to the surface around 5 AM. Two hours later, it was recovered using a small dinghy. The ship crew was able to safely lift the instrument up to the ship's deck. Today, the Marion Dufresne continues on its path along the ridge.

As a test for next year, our colleague Wayne Crawford had dropped an absolute pressure gauge close to one of the first array stations. After all eight seismometers had been deployed, the pressure gauge was called back to the surface around 5 AM. Two hours later, it was recovered using a small dinghy. The ship crew was able to safely lift the instrument up to the ship's deck. Today, the Marion Dufresne continues on its path along the ridge.

Long night on the mid-ocean ridge

Written by Karin Sigloch on Tuesday, 16 October 2012.

16 October 2012

Long night on the mid-ocean ridge

We are preparing for the most intense part of our cruise. In roughly two hours, we will arrive at a special, well mapped segment of the Southwest Indian spreading ridge, where we will deploy 8 OBS and one absolute pressure gauge in the space of 30 km x 60 km and less than one day. This OBS sub-array was initiated our colleague Vera Schlindwein, who investigates the structure and functioning of mid-ocean ridges that spread extremely slowly, using earthquakes that the ridges generate. We will have many additional uses for these data, including contributions to imaging the Réunion plume from a long distance.

Since reaching the southernmost point of our deployment at 34°S two days ago, we have been following the Southwest Indian Ridge in northeasterly direction. On an endless, almost flat ocean, it is unreal to conceive that four kilometers beneath us runs part of the largest mountain range on earth, a segment of the global ocean spreading system. Our only sensual connection to that world is the bathymeter, which also shows only narrow swaths of those vast mountains, but drives home the point nonetheless: for several OBS deployments in a row, shifting a site by a few kilometers would also have meant altitude differences of 1000 meters and more – target the edge of the rift valley or drop into the deepest abyss?

For the upcoming OBS array, it will be mostly the center of the rift, plus one volcano that peaks up to "only" 3000 m depth. Having practiced on 40 sites at a relatively leisurely rate, we're eager to ramp up the game in this spot, during a fast-paced night and morning.

An abandoned plaza

Written by Carmen Gaina on Saturday, 13 October 2012. Posted in Cruise 2012

13 October 2012

An abandoned plaza

During the night and early morning we have "descended" from the Madagascar Plateau (a submerged large plateau situated south of Madagascar) towards an old abyssal plain that formed while India was heading north, away from Antarctica and Africa. This relatively small patch of oceanic crust, almost surrounded by the higher Madagascar plateau seems to have a special story. The maps we had before this cruise revealed some fan-like linear highs and valleys, and now, freshly collected swath bathymetry data reveal indeed nice linear features with different directions converging to some northerly situated point.

In the past, when the dinosaurs were enjoying their (almost) last days on Earth, and before the South West Indian ridge carved its way through the Indian plate, this particular point might have been the meeting place between the three good old friends: the Antarctic, Indian and African plates. They met there at the so-called triple junction and while chatting and holding hands they brought more magma to the surface and grew together. Some unexpected (unhappy?) event forced them to abandon that place and go somewhere else, and build a new "plaza". Now, this abandoned site, sits oddly next to some younger neighbors and invite us to scratch our heads trying to decipher its mystery.

The way they were…

Written by Carmen Gaina on Thursday, 11 October 2012. Posted in Cruise 2012

11 October 2012

The way they were…

For the last two days we were collecting data and deploying OBS in the southern Mascarene Basin, following "highways" from the youngest part of this ocean (about 60 million years) to the oldest part (probably older than 80 million years). Yesterday we have reached one of the points closest to Madagascar, and therefore had a "glimpse" at the early history of this region.
This sent us back in time approximately 80 million years ago – so how was it like back then?

Well - first of all, Madagascar was much closer to the Indian subcontinent and the Mascarene basin was in his early days (I mean million years). At that time they were both travelling northward from southern latitudes (northern Madagascar was situated at about 30 degrees south), having left Antarctica in the Mid Cretaceous time. Older oceans in the vicinity (the Somali and Mozambique basins) already reached maturity by the time new oceanic crust started to form between India and Madagascar. Shortly before that happened, bursts of volcanic activity affected Madagascar's margins and probably formed a huge volcanic plateau south of it - the Madagascar plateau. This was because at that time, another plume, older than Reunion – the Marion plume, was in the vicinity of the southern Madagascar (and the incipient Mascarene oceanic basin) and created magmatic pulses now and then. Whether this also reached the young Mascarene basin – is difficult to say –but we do see some unexplained higher plateaus close to the SE Madagascar margin, and believe that a tiny portion of it was imaged by the multibeam system just yesterday.

The following map, despite its (too) bright colours is a real map that catches a moment in the Mascarene basin's childhood. Decades of geological and geophysical data collection, interpretation and modelling makes now possible to construct such a snap in time. One can observe the position of the main land masses and their older history (geology from Archean to Cretaceous), around them reconstructed oceanic seafloors (shown by the present day free air gravity-which can give an idea about the structure of the oceanic crust under the sediments), and even an ocean that doesn't exist anymore, consumed by subduction somewhere between India and Arabia. The location of the mighty Marion plume is also shown, as we can trace back its position through knowledge of plate tectonics and mantle dynamics.

This story will have more details in the months and years to come, once the data collected now will be processed and interpreted by the RUM-RHUM project participants. And it will help us understand the tumultuous life of the Indian Ocean at the time of significant tectonic and magmatic activity that may have contributed to global changes like sea level rise and changes in seawater geochemistry. Stay tuned!

Rendez-vous of OBS

Written by Florian Schmid on Thursday, 11 October 2012. Posted in Cruise 2012

11 October 2012

Wayne explains the French OBS instrument to Kasra, Erik and Henning.

For the second Leg, three French OBS specialists joined us with their nine instruments, and it becomes more and more colourful on the working deck. While the German OBS team is residing 'upstairs', occupying the helicopter deck and hangar of the ship, the French team lives 'downstairs' on the main deck.

Driven by the thrill and curiosity on both sides, yesterday a rendezvous was organized for all OBS specialists to present the each other the components and working principles of the surprisingly different systems.

As the German lobsters are rather flat and compact, the French instruments remind somehow of Mars rovers that will eventually invade the sea floor. One of the main differences is the separation of the seismometer unit from the rest of the instrument in the French systems. It is still actively debated among seismologists whether or not this has a strong impact on the quality of the data. We are all the more interested in next year's recovery of the instruments, when the seismic curves will tell us more about the virtues and vices of either system...

A German “Lobster” OBS (orange) lends company to a French OBS on the working deck before its deployment.

First French OBS deployed

Written by Karin Sigloch on Thursday, 11 October 2012. Posted in Cruise 2012

11 October 2012

Last night the first French OBS was launched. First deployments are special, so the event was well attended despite the late hour. Unfortunately, night deployments are not easy to capture…

Last night the first French OBS was launched. First deployments are special, so the event was well attended despite the late hour. Unfortunately, night deployments are not easy to capture...

...so here the same thing again in bright daylight. French OBS #2 started its voyage to the ocean bottom this morning. Seven more will follow, interleaved with 25 German OBS. The advantage of the French model is that it records seismic waves down to lower frequencies.

…so here the same thing again in bright daylight. French OBS #2 started its voyage to the ocean bottom this morning. Seven more will follow, interleaved with 25 German OBS. The advantage of the French model is that it records seismic waves down to lower frequencies.

End of Leg 1 -- heading south now

Written by Karin Sigloch on Thursday, 11 October 2012. Posted in Cruise 2012

8 October 2012

20121009 01 EquipeLeg1 J2Z0192

 The first leg of our cruise ended today. As the Marion Dufresne approached La Réunion in the morning, visibility of the 3000 m high volcanic island was excellent. Our dream is to image equally clearly to 3000 km depth. (Photo: Nicolas Villeneuve)

 

20121009 02 SAM 0968

Entering Le Port and relieved to see that the large harbor machines were working. We had arrived one day early just to avoid another harbor strike tomorrow.


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 In the early evening, we had to say farewell to 11 colleagues, who had been interested mainly in exploring the region around the Mascarene islands. Leg 2 will consist of a 7000 km long round to the far south of the islands. Six new colleagues came onboard, among them the French OBS team with another 9 seismometers.

 

20121009 04 MD depart SAM 0998

All unloading and loading got done in time. We left the harbor late in the evening, happy to get back onto the ocean.

 

 

The whale and the butterfly (digression about rounds on the water)

Written by Jérôme Dyment on Monday, 08 October 2012. Posted in Cruise 2012

7 October 2012

On Rhum-Rum, we are not doing rounds in the water...  but nice drawings indeed!

Of us, marine geophysicists, who wander on the oceans, looking for indices to better understand how the seafloor forms, ages, and disappears, some are saying that we are doing rounds on the water. It is untrue, indeed! A short glimpse to the route map of cruise Rhum-Rum - routes achieved during the first leg, routes to be done during the second one - clearly shows that, if we do accumulate some mileage, it is certainly not doing circles but much more complicated figures, which await patiently an improbable Sigmund Freud to decipher their deep meaning, their psychoanalytic signification. This aspect appeared to me when, just after my PhD thesis - otherwise said in the Middle Age - I boarded the first Marion Dufresne for cruise MD67. Possibly affected by our short stop in Kerguelen Island when approaching the study area, our path was drawing a giant penguin superimposed to the structures of the Kerguelen Plateau and the Enderby Basin. Years later, when I was leading cruise Magofond 3 on R/V Suroît south-east of the Canary Islands, I rapidly noticed that our tracks were making a big M then a smaller A - we did not reach the end of the word, but were then making deep-towed magnetic profiles across the Cretaceous Quiet Zone to try to unravel one of the greatest remaining enigmas of geomagnetism. And today, finishing Rhum-Rum Leg 1, the two wide loops that we made to the East - almost touching Rodrigues, and Mauritius twice - and to the West - in a rather shy approach to the Big Island of Madagascar - let me think of the (truncated - we lost 6 days!) wings of a giant butterfly (Figure 1), whose body would be made of the inner circle of ocean bottom seismometers that we consciously dropped all over around La Reunion Island... Should we imagine the caterpillar, moving up from the deep Earth mantle with ascending currents of the inferred plume, cocooning in the heat of the Fournaise then metamorphosing to butterfly and taking advantage of our cruise to escape, like an allegory of the Truth coming out of the well - I wouldn't dare to say in what apparel!

As I write Leg 2 remains to be done, and I will unfortunately not be there to contribute more than through some maps - again - left onboard to the best use of the chief scientists. I already see, in the projected tracks, the shape of a whale (Figure 1), its noose on the Rodrigues Triple Junction - this peculiar point where three mid-ocean ridges meet. The whale's front follows the Central Indian Ridge, its mouth would be located in that small area of the Southwest Indian Ridge where eight ocean bottom seismometers will be deployed very near to each other - may be to detect a possible raging "baleenache"... Paradoxically, I imagine the dorsal fin on the side without any active ridge ("dorsale" in French), in the Madagascar and southern Mascarene basins, as an indication of other, fossil spreading centers that we would not have properly detected yet.

Now you know why I entitled this essay "the whale and the butterfly". It is open to analysts and other psychiatrists, professional or not, to further investigate the matter - delirium is not unusual in geosciences!

“It’s déjà vu all over again”

Written by Karin Sigloch on Monday, 08 October 2012. Posted in Cruise 2012

6 October 2012

“It’s KUMing home” – was it them who told the dock workers that the Marion Dufresne would be back in port?

"It's kuming home" -- Was it them who gave away the Marion Dufresne's return to port?


Halfway through the experiment, we were going to stop briefly in La Réunion on October 9, in order to pick up more colleagues and material. And guess what, yesterday the dock workers announced a strike for that day. No joke. This time a nationwide general strike of harbor workers and others.

The human mind tries to make sense of things. The first strikes in 10 years, and both on the only days that we need the dock workers? They must have been missing us, our friends from the dock – longing for another rendez-vous at the harbor gate, no doubt. Has nobody else been talking to them since we left? Who has leaked the plans for our stopover, and how do we plug this leak, given that we'll have to return to port once more at the end of the cruise?

But they blundered, this time by giving us more than 24 hours notice. Yesterday was spent with frantic phone calls and deliberations, a scramble to advance our port visit by one day: to rush in our colleagues from Europe for Leg 2, to accommodate the people leaving, and to design a new deployment route that minimizes the loss of time. Plans for this counterstrike are well advanced: Rendez-vous in Le Port on the 8th – in full working gear!

Seismic Rock

Written by Jean-Paul Montagner on Friday, 05 October 2012.

Poème sismique by Jean-Paul Montagner

Seismic Rock

De la musique sismique,
Nous sommes des fanatiques,
Malgré tous les dockers,
Nous sommes ses rockers,

Les ondes sont nos rockstars,
Jamais ne sont en r'tard,
Et chantons tous en coeur,
Nous sommes ses rockers.

Faisons valser les ondes,
Elles traversent le monde,
Elles n'aiment pas les frontières,
Elles traversent les mers,

Avec les Obéesses,
Nous avons nos déesses,
Et plus rien ne nous freine,
Sur le Marion Dufresne,

Les ondes sont les rockstars,
jamais ne sont en r'tard,
Et chantons tous en coeur,
Nous sommes ses rockers.

Floating seminar

Written by William Jason Morgan on Thursday, 04 October 2012. Posted in Cruise 2012

4 October 2012

Detailed bathymetry measured by our ship has been laid over a coarser, pre-existing deep-ocean map. Note the canyon that appears on the highly resolved swath. The swath is about 10 km wide, the canyon is located around 3000 m depth.

One of the more interesting aspects of a research cruise is the 'floating seminar' atmosphere. I don't mean the daily afternoon presentations in the conference room by one of the cruise participants, as interesting as they are, I mean the daily interactions of persons with various specialties from various institutions all focused on a single research project. Seeing how the ocean bottom seismometers (OBSs) are assembled, tested, deployed over the side (gently!); having discussions of what can go wrong, tales of past mistakes, improvements being made all give one a better understanding of how a seismic experiment is planned and executed far beyond what one can get from reading journal articles of OBS results.

Another center of activity and discussion is the monitor screen that displays each 'sweep' of the incoming bathymetric data. The 'multibeam' bathymetry of the Marion Dufresne has acoustic sensors that look not only straight down to the seafloor but also are aimed outward to receive echos from many angles away from straight down. Then the return echos of the many sensors are put together in the system's computer, and a 'swath' of bathymetry is produced. The moving ship results in a ≈5-km-wide ribbon of seafloor depths mapped, analogous to laying out a series of aerial photographs for land mapping.

The general locations of each OBS site were selected when the experiment was planned, but the precise location for a 'drop' is made while looking at the bathymetry collected at the site. At this time, many eyes gather in the lab around the bathymetric screen -- all looking for that perfect flat, not too rocky, not too steep spot on the ocean floor. Lots of murmur in the peanut gallery as Karin and Guilhem make the final choice -- sometimes the initial 'X' is abandoned and a 'better' place several kilometers away is selected instead.

The bathymetric screen showing the swath of bathymetry collected as we steam from drop-point to drop-point is a constant focus of interest. Many so-called "seafloor canyons" have been seen in the swaths. These features are tens of meters deep and hundreds of meters wide; they are commonly made by avalanches on the steep slopes of continental shelves which create a fast moving mixture of water and suspended sand which cuts away the flat mud on the seafloor much like a river cuts away land surface. Near continents, such 'canyons' can be traced for hundreds of kilometers; the source here mid-ocean would most likely be collapse of the slopes around the carbonate banks and islands of the Mascarene Plateau. Our cruise isn't mapping them -- following them from beginning to end -- but we have crossed and noted perhaps a half-dozen on our zig-zag path from site to site and wonder collectively where and how each may have originated.

And last night the sky was brilliant; a bright Milky Way and the bow of the ship pointing directly toward the Southern Cross.

To drop or not to drop?

Written by Karin Sigloch on Thursday, 04 October 2012. Posted in Cruise 2012

4 October 2012

Annotated map describing an OBS deployment (station RR17). (Read more bellow)

Among our most crucial decisions is where on the seafloor to drop our seismometers. Geometrically, the task is not unlike dropping them from an airplane at 3-6 km altitude, hoping that they will land in a suitable spot. Some luck is needed, because the seafloor is not mapped down to the meter scale, and because ocean currents can carry the OBS away laterally by several hundreds of meters before they reach the seafloor.

However, careful preparation can maximize the chances of a successful landing. The most basic requirement: the instrument should be recoverable when called to return to the surface – that may not be possible if it landed in a crevasse or tumbled over on a steep slope. Hence we seek out relatively flat spots of at least 1 km2 area. Such places can be found even in (underwater) mountain ranges, but dropping an OBS there requires more preparation than on a vast abyssal plain.

The other morning we had a challenging case, a targeted OBS site on the steep flank of the Mascarene plateau. The only prior bathymetry information came from "Sandwell", a jargon referring to maps extrapolated from measurements of gravity satellites – very smoothed and blurry sea-scapes compared to reality, but much better than nothing (see annotated map). "Sandwell" suggested a little flat embayment in the plateau flank, but as we approached, the highly-resolving ship bathymeter gradually revealed a steeply incised canyon, 2800 m beneath the surface. No sediments to flatten out even a small area. We collectively pondered the evolving scene, and imagined mud avalanches rushing down the canyon channel. Fact or fiction? No way to tell. It seemed unwise to drop the OBS there.

With not many options available, we targeted a small protruding ledge a few miles up-flank on Sandwell's map. The approach was steep and unpromising, but suddenly sediments started showing up on the screen of the sediment sounder. The saddle area turned out to be narrower and shifted compared to the Sandwell prediction, but 1.5 miles wide and reasonably flat seemed lucky under the circumstances. We dropped the OBS above the likely equivalent of an Alpine meadow, bounded by a steeply incised mountain stream, perhaps with bottom-dwelling fish instead of grazing cows. It had taken us two hours, but had also satisfied our curiosity. Expert bathymetrist Jérôme summed it up: "Interesting – so that's what a canyon may look like for Sandwell."

* Picture Caption : 

Annotated map describing an OBS deployment (station RR17). Before our arrival, we had only the blurry bathymetric information that fills most of the picture (“Sandwell”, extrapolated from gravity satellite measurements). In real time, we replaced a ~10 km wide swath beneath our ship track with the ship’s own, more highly resolving measurements (top left to bottom right). It revealed that the seafloor in this area was not smooth at all – it took some cruising to find even a small flat spot.

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