RHUM-RUM 2013 in a 4' video

Written by Guilhem Barruol on Saturday, 04 January 2014. Posted in Cruise 2013

The RHUM-RUM OBS recovery in 4 minutes on youtube

 

A GoPro video summarizing in 4 minutes the RHUM-RUM 2013 experiment!

GoPro Hero 3 : Ocean bottom seismometers RHUM-RUM     

Kindly prepared par Emile Barruol

 

 

End of second RHUM-RUM cruise in La Réunion

Written by Guilhem Barruol, Karin Sigloch on Saturday, 07 December 2013. Posted in Cruise 2013

4 December 2013, Karin Sigloch & Guilhem Barruol

 

Wednesday, 4 December at 5:00 in the morning, La Réunion Island is lying ahead of us in the first daylight -- our cruise is ending here.

The "Marion Dufresne" arrived in Le Port together with us.

We made a fuel stop in Mauritius yesterday. During our overnight transit to La Réunion, the research vessel Marion Dufresne had stayed by our side the entire time. They too had been filling their tanks on Réunion’s enterprising sister island, but for us, the unexpected company of “Le Marion” during our last cruise night meant a bit more. It was with this French ship that we began our experiment and deployed our seismometers 14 months ago. Being accompanied home to Le Port by Le Marion, with all OBS recovered onboard the German Meteor, gave a beautiful sense of closure.

Things are moving in European marine geophysics!

Thank you very much to the science party of cruise M101, and to those who will now work hard on the data, in order to illuminate one of the darker corners of the interior of our beautiful planet.

And thank you very much to the crew of the Meteor for their dedication, professionalism, and good humor at all times of day.

Vielen Dank und auf Wiedersehen!

Karin & Guilhem

 

Science team of cruise M101, Leg 2.

 

The eternally unfinished business of science

Written by Karin Sigloch on Saturday, 07 December 2013. Posted in Cruise 2013

3 December 2013, Karin Sigloch

Tuesday, 3 December at 9:54: Marine geophysicst Dass Bissessur turns off the multi-swath bathymetry – end of data acquisition on cruise M101. Of course there would be more to do, but our time is up.

Shortly afterwards, we are cleaning the labs that have served us so well as work places over the past 40 days, while the Meteor is fueling just outside Port-Louis harbor, Mauritius. Now we only need to transit to La Réunion until tomorrow morning.

We were lucky that the weather had never been bad enough to prevent or delay OBS recoveries. When all 57 seismometers were back on Day 35, we found ourselves with a few unused days of ship time, which we decided to use on a bathymetric and magnetic survey northeast of Mauritius. The target was a smaller, east-west striking chain of underwater mountains that trends away from Mauritius into the “Rodrigues segment” of the Africa/Somali plate. As far as we could tell, it had never been mapped with a modern multi-swath bathymeter. We are interested because it may represent part of a suspected magmatic flow channel at 100-200 km depth, which may be transporting hot rock from the Réunion hotspot to the Central Indian spreading ridge. Thus the hotspot might be “spiriting away” its heat largely undetected (a state of things that we would want to end).

It was an exploratory survey. Three days are not much, so we had to design with a rough brush, trying to guess from the coarse satellite maps where the top of the ridge might be running, and where to attempt a couple of passes over the flanks. Coverage gaps were inevitable. The above plot shows the result, a 3-D rendering of the mountain chain. It was found to have an elongated flat top, which means it probably emerged above sea level sometime in the past, but now it lies 350 m below sea level (the bathymeter beam shrivels together to not much more than a line at such shallow depths, hence the big "hole" at the centre of the image).

There is bound to be an interesting tectonic/volcanic story, but it’s clearly an unfinished project, like almost all endeavors in science. We’ll scratch our heads, try to come up with reasonable hypotheses, and hope that someone can return for a second look not too long from now.

Mauritius like nobody has seen it before

Written by Christine Deplus, Dass Bissessur, Jérôme Dyment on Monday, 02 December 2013. Posted in Cruise 2013

A new bathymetric view of Mauritius Island

 

While the second leg of cruise Rhum-Rum 2 is on its way, researchers who left at the end of the first leg have started to work on the data collected during this leg. Of particular interest is the bathymetric survey achieved around Mauritius. A preliminary analysis of the raw swath data has been undertaken and the resulting digital elevation model was merged with those resulting from multibeam bathymetric data collected during previous cruises. Together, they reveal a view of Mauritius that nobody has seen so far.

Showing Mauritius as a whole, standing almost 5000 m above the seafloor (4000 m below sea level added to the 828 m of the highest mountain of the island), this new bathymetry offers a much more complete picture of the volcanic edifice than any map or photography limited to the island. Erosion gullies run down the slope from both the east and west coasts. Successive fronts of debris and sediment accumulation are clearly imaged at the foot of the southwestern slope. South of the island, many submarine volcanic edifices continue the N20°E volcanic alignment that cut across the island and produced the most recent "younger series" described by the geologists on land. Volcanic aprons observed east and southwest of the island may represent the "rift zones" which focused the volcanic activity at the origin of the shield volcano.

This preliminary map will be completed by data collected during the second leg. The older data will be reprocessed to achieve a better resolution. Although further work is required to propose a complete interpretation, it is already clear that these data will provide a new vision of Mauritius geological history.

Dass Bissessur, Christine Deplus, and Jerôme Dyment.

 

Mauritius bathy1

 

 

Perspective views of Mauritius from azimuths 150°E (top) and 250°E (bottom), elevation 30°, and vertical exaggeration 2.5. Different bathymetric data show various resolutions: the largest, pale colored pixels correspond to bathymetry derived from satellite altimetry (Smith and Sandwell, Science, 1997), whereas the bright colored pixels correspond to multibeam bathymetry of different resolutions (Magofond 2 (1998), Gimnaut (2000), Forever (2006), Knox11rr (2007), Rhum-Rum 1 (2012), Rhum-Rum 2 (2013)). 

 

All seismometers are back!

Written by Guilhem Barruol, Karin Sigloch on Saturday, 30 November 2013. Posted in Cruise 2013

29 November 2013

 

 On another gorgeous day, now 200 km southeast of Mauritius, we pulled ocean-bottom seismometer RR56 out of the water – our last instrument is back. Its ascent may have been accompanied by a whale. The big animal surfaced directly next to the ship immediately after we had pulled the OBS onboard, and dove back and forth beneath the ship’s hull twice before disappearing into the blue. A farewell from Neptune? The science party greeted back with excited shouts in any case.

57 OBS deployed, 57 recovered a year later: big relief among technicians and scientists because the marine environment is harsh, technology has its weaknesses, and losses would not have come as a surprise. Some luck is definitely needed, but when you achieve a recovery rate of 100%, you also know that you did something right. Thank you very much to our extremely professional OBS teams: Erik, Edith, Maria, Kasra and Juan for the German instruments, and Romuald and Xuan for the French OBS!

RHUM-RUM in Madagascar

Written by Karin Sigloch on Saturday, 30 November 2013. Posted in Cruise 2013

28 November 2013, Geneviève Roult, Karin Sigloch

As part of the terrestrial component of the RHUM-RUM experiment, we installed five broadband stations in Madagascar in 2012 together with professor Gérard Rambolamanana and his team from the University of Antananarivo. They were deployed along the southeast coast, more precisely in Manakara, Farafangana, Manambondro, Manantenina and Mahatalaky. The stations should be checked and maintained about twice a year, so this November 2013, while we were at sea, our colleagues Christophe and Richard from the University of La Réunion for the third time did the tour from Tanararive to Fort-Dauphin. And what a tour!

The rainy season had unfortunately started early this year, and the condition of the route had gone from bad to worse. The car broke down, so that halfway through, a new car had to be called in from the south. The rivers had flooded, and river ferries, many of them man-powered, had become dangerous. All the experience of our local drivers was also needed for crossing the numerous river fords. The colleagues almost got stuck but finally arrived in Fort-Dauphin safe and sound – tired, but with a good harvest of seismological data.

The 5 seismological stations will stay in place until at least May 2014, but ultimately need to be dismantled and repatriated. We are still welcoming volunteers to go on the road with us in Madagascar then…

 

Second Mermaid released into the sea

Written by Karin Sigloch on Tuesday, 26 November 2013. Posted in Cruise 2013

25 November 2013, Karin Sigloch

Launch of the second of two MERMAIDs, novel seismological sensors for the oceans.

Today just before leaving station RR52, we deployed a "MERMAID", a novel kind of seismological sensor for the oceans, developed by the University of Nice. A MERMAID is an Argo float that is adapted to deliver data for global-scale seismic tomography, i.e., studies that compute the 3-D structure of the earth's mantle, using signals generated by naturally occurring, distant earthquakes. Very few seismometers are deployed in oceanic areas: islands for land seismometers are sparse and unevenly distributed, and OBS are expensive and high in maintenance. The MERMAIDs, which float around passively in the oceans, are designed to fill this data gap.

Thousands of Argo floats have already been deployed by physical oceanographers, hence the "carrier" component of MERMAID technology is reliably in place. Inside sits a hydrophone to record sounds in the water column, and processing hardware and software to decide whether any of the sounds are due to earthquakes. Seismic waves traveling through the solid earth hit the ocean bottom from below, where some of their energy is converted to an acoustic wave. If the MERMAID, usually drifting at around 1000 m depth, detects this kind of acoustic signal, it rises to the surface and transmits its information to its owner via satellite communication link. Then it sinks back to the deep and waits for the next earthquake.

The two Nicean MERMAIDs were supposed to be deployed together with our RHUM-RUM ocean-bottom seismometers in 2012. They would have floated around inside our network, and signals from the two types of sensors could have been compared. Unfortunately the MERMAIDs were not finished in 2012, so that now their journey will be a lonelier one, though no less interesting. On 24/11 a sizeable earthquake (mb 5.1) occurred on the triple junction, just hours after we had recovered our station RR50 there -- no luck. But we had also released the first MERMAID there, and it has already sent home its first earthquake alert.

All nine French OBS are back

Written by Guilhem Barruol, Karin Sigloch on Monday, 25 November 2013. Posted in Cruise 2013

25 November 2013

 

 

Under a gorgeous tropical sun, no wind, calm sea, we recovered the last of nine French OBS from the INSU instrument pool. Relief was written on the faces of our two engineers Romuald Daniel and Xuan Li, who had worked hard to ensure the good functioning of the instruments and their safe return to the surface. So the hardware recovery was 100%, and we estimate that the overall data recovery rate (duration of useful functioning) for these 9 OBS will be around 80% -- a very good result for this kind of experiment, especially since several of the instruments had been deployed for the first time. Bravo and thanks very much to Romuald and Xuan.
We need to recover 4 more of the 48 German OBS, and we are awaiting them impatiently.

 

"The Sun, the Sun, from the Meteor"

Written by Karin Sigloch on Monday, 25 November 2013. Posted in Cruise 2013

24 November 2013, Karin Sigloch

 

Chance encounter in the Indian Ocean: research vessel "Sonne" in the foreground, "Meteor" in the background.

"The Sun, the Sun, from the Meteor" -- the German equivalent of this call went out from the ship radio this morning, when our captain called another ship barely visible on the horizon. It is a rare occurrence for two research vessels to meet unscheduled on the open ocean. For the two big German vessels "Sonne" ("Sun", in service since 1977) and "Meteor" (1986), it was the first time ever, and will almost certainly remain the only time, since the "old Sun" will be retired upon her successor's launch in mid-2014.

Hence we really wanted to meet when ten days ago we learned that the Sonne would be mapping the Central Indian spreading ridge in the immediate vicinity of our station RR51, and in just the right time window. The chief scientist on the Sonne agreed, which generated considerable excitement among the crews of both ships as well.

 

It was a majestic moment when the venerable "Sun" crossed ahead of us around noon and laid itself beside the Meteor. Unfortunately this photo could not capture the music. From big loudspeakers, we greeted the colleagues with treasures from the German lieder trove: heart-warming pop from the past century ("Where my sun is shining", "Red sun of Barbados"), followed by Rammstein's "Here comes the Sun" and "If I'm not here, I'm on the sun deck".

 

Before long there was indeed busy  boat traffic between the decks of the two ships. We marveled at how this former fish trawler, built in 1969, is still equipped with the most up-to-date research infrastructure. Around 5 p.m., we parted ways again to continue our work, very pleased with the special Sun-day we had spent.

Holes in the crust

Written by Carmen Gaina on Tuesday, 26 November 2013. Posted in Cruise 2013

22 November, Carmen Gaina

 

Seafloor depths at three different scales of zoom. Arrow points at a deep depression of -5500 m, even though the area is nominally located on an underwater mountain chain, the Southwest Indian spreading ridge (3-D renderings by C. Gaina using newly acquired bathymetry data).

We’ve been cruising along the Southwest Indian Mid-Ocean Ridge for a couple of days now, and we get to see more and more its effort to break through old oceanic plates. The ridge is bending and splitting, trying hard to establish itself between the older neighbours. And then we see the “Holes”! It is like the Grand Canyon of mid-ocean ridges, but this abyss bottoms out more than 5000 meters below sea level. Cliffs rise up more than 2500 meters to either of its sides. They expose rocks that are only about a million years old, instead of billions of years on land -- just a blink in geological time. Here the Earth’s crust is ripped apart until its flesh is laid bare -- the mantle.

At mid-ocean ridges, new crust is being added every year, and this is how tectonic plates are growing and moving away from each other. However, in rare places such as this one, only a small amount of magmatic material is added to the new plate boundary, not enough to fill the gap left by the divergence of the two ridge flanks. Oceanic crust is stretched until the mantle underneath rises to the surface. The Southwest Indian Ridge and the Arctic Gakkel Ridge (the so-called ultra-slow spreading ridges) are the only places on Earth where these extreme processes produce deep “holes” where one can peer through the oceanic crust into the mantle, and find out its deep secrets.

 

Captain’s Blog (2)

Written by Alice Gabriel, Michael Schneider on Saturday, 23 November 2013. Posted in Cruise 2013

18th-19th of November 2013, Michael Schneider, Captain of the "Meteor"

20131120 DrehungMeteor

After station RR35 "METEOR" turns on the heel

 It has turned midnight on the 18th of November as OBS RR35 is released and rises. Last estimates expect it to surface around 0030, let’s see where it will arise. OBS’ are always good for surprises and such is this, as it surfaces in distance of only 2 hawsers (370 meter) and 4 points (45 degree) port side. It takes us a short swerve to port side immediately followed by one to starboard to retrieve it, just as the previous four, as the fifth French OBS safely and successfully onto deck.

For the instrumentation initialization of the subsequent profiling using multibeam and magnetometer Meteor turns via starboard in less than 4 minutes to the new course of 39 degrees describing a near-perfect circle of radius 55 meter – given the ship’s length of 100 meter we literally turn on the heel.

The day is spent profiling and in the early evening hours, before sunset’s evening glow, OBS RR37 is collected. After a transit time of 10-12 hours the next one will appear and ask for a ride. Finally, in the morning of the 19th shortly before 0800 OBS RR38 emerges and is recovered just as all others before. It was letting us wait, maybe to dress up for us. This night we are hard-working on recovery and tomorrow morning we head to the next French OBS: slowly but surely they become less and sooner or later we will get them all!

The cute little depression in front of the coast of South Africa which German Weather Service describes creeps east and its frontal cloud band will not affect us too much, since we are driving further northeast. Thus, slight weather improvements and increasing sun hours accompany "METEOR" as we are heading towards "SONNE" (“SUN”). During the weekend we stand a good chance for the routes of the two German research vessels "METEOR" and "SONNE" to encounter for the first time in their long marine lives. However, encountering may not be the most suitable diction, since it may imply both of them coming to a bad end :)

 

Towards the "SONNE"

Halos

Written by Alice Gabriel on Monday, 18 November 2013. Posted in Cruise 2013

16 November 2013, Alice Gabriel

 

Leaving Le Port into the flat seas surrounding Reunion we were stunned by a colourful circle surrounding the sun in the otherwise blue sky. The ring, surrounding the shallow sun at a distance of 22 degrees, is the most common of more than 50 known 'Halo' effects. These originate from sunlight scattering off ice crystals, stemming for example from Cirrus clouds at great heights.

The sailor's proverb ‘a Halo foretells bad weather’, came true as we did indeed experience storms in the following days. Gusts of wind, rain, thunder and up to 3 metre swell plus 2 metre wind sea accompanied us on our way South-West. That which is bad news for the newcomers (and their stomachs) is good news for the on-board weather observatory: finally an interesting weather situation beyond 'boring' high pressure cells! In the coming days we can watch registering balloons rising up to heights more than 20 km, measuring temperature, air humidity and pressure and transmitting data via radio and satellite directly into German Weather Service network.

Thus, not only we can prepare for the weather and ocean conditions awaiting us, but our cruise also contributes to global weather observations enabling, for example, ecological friendly fuel optimized air routes.

Captain’s Blog

Written by Alice Gabriel, Michael Schneider on Thursday, 21 November 2013. Posted in Cruise 2013

12th-16th of November 2013, Michael Schneider, Captain of the "Meteor"

French OBS on deck

On the 12th of November 2013 we depart La Reunion just in time. The local pilot leaves the Meteor 15 minutes after we have gone out from between the mole heads. We start for the recovery of the remaining ocean bottom seismometers.

 

The first and second OBS are of French make and since they are apparently more vulnerable than the German ones I will personally collect all of them. In total, we will collect 9 OBS of French type; all others are “ordinary” ones of make KUM Lobster.

In the early morning of the 13th, at 0430, the collection of the first French OBS does not cause any problems. Around 2300 during the following night it is then the turn of the second one. Naturally, it is raining, and shortly before the retrieval attempt onto the starboard deck the OBS moves hard port, thus I have to reverse slightly and then swerve forwards. Besides the rain we experience northeastern winds of strength Bft. 4 and a southsoutheastern swell of 3 meters heights and periods of 8-9 seconds – all of which does not simplify our task. The OBS now appears at port side and I have to move the vessel again in order to bring the OBS to starboard while causing as little rolling as possible and utilizing the wind. This leads to a wind direction from starboard. However, on top of the unexpected wandering of the OBS from starboard to port side, for the collection procedure a port side wind is required. Of course, this is not the fault of the OBS, but rather mine, I should have paid more attention.

In the morning of the 15th of November another French OBS is scheduled for recovery, after Heike, the chief mate, retrieved a KUM type instrument in the early afternoon of the previous day. This time, the OBS labelled ‘RR31’ surfaces at starboard around 30-50m athwardships of stern. Since the wind direction is orthogonal to starboard, of course the vessel has to be turned, whereby it carries off the OBS. But finally, the OBS reaches the Meteor almost directly at its gate and can be collected without problems. The following two OBS are again KUM instruments succeeded by another French OBS which is expected in the evening around 2030. Just as scheduled, it surfaces shortly after 2100, but quite far away at starboard aftwards. The wind is blowing quite intensely with Bft. 5 from starboard and thus Meteor drifts after turning and under influence of the wind from backboard with partly more than 2 knots towards the OBS. Also this instrument can be collected successfully without further problems onto deck at 2143.

The weather conditions regarding winds will develop favorably, i.e. we expect a decrease of wind strengths, but the swell will remain at 2 to 2.5m. This does not affect our profiling but poses challenges during recovery of the OBS, causing rolling episodes of the vessel and eventually slopping of the soups out of our plates.

 

 

Recovery of a German OBS ("KUM Lobster")

 

 

Shark attack on the magnetometer

Written by Karin Sigloch on Sunday, 17 November 2013. Posted in Cruise 2013

16 November 2013, Karin Sigloch

 

 

Our magnetometer seems to have been bitten by a shark last night. We haul it on deck prior to every OBS recovery, and this morning it came in with significant damage. Its plastic casing bore scratch marks in numerous places and a couple of deep bite holes, from which the thick casing had cracked outward in irregular patterns.

 

 

Colleagues and the Meteor's crew were aware of similar assaults on towed equipment in the past. The magnetometer is 120 cm long and has a slender, fish-like shape. It is pulled along on a 250 meter long cable that transmits data to the ship in real time. Magnetometers could be particularly interesting to sharks because they generate weak electromagnetic fields, which the predators may be able to sense.

The interest is not mutual. The magnetometer measures neither biological signals nor properties of the water column. Rather its purpose is to record the magnetization that is "frozen" into oceanic crustal rocks, from the time each parcel of seafloor originated from molten lava along an oceanic spreading ridge. Magnetometers record spatially alternating patterns of seafloor magnetization as the ship passes over, and these patterns can be tied to the timescale of polarity flips of the earth's magnetic field. Together they tell the story of how ocean basins have originated, grown, and vanished over geological time. The part of the Indian Ocean we are currently passing through is particularly old, dating from times for which information about the configuration of continents and oceans is sparse. Unfortunately our magnetometer will have to stay on board for now, until we are convinced that its hull is still waterproof.

 

First French recovery

Written by Karin Sigloch on Friday, 15 November 2013. Posted in Cruise 2013

13 November 2013, Karin Sigloch

 

 Today in the earliest morning hours, we recovered the first French OBS (station RR28). The operation had been preceded by some additional technical preparations because this model needs to be approached by the ship even more carefully than its German counterpart, and it consists of two pieces that can start to swing as a double pendulum while being lifted out of the water. RR28 also didn’t reply to its release command (at least not audibly), leaving us to worry for three hours whether it would appear or not. When it finally did, its recovery went smoothly despite a relatively rough sea, and the seismometer has brought back very nice data.

 

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