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Report from research vessel Sonne

From the 4th of October to the 2nd of November an international research cruise sails to the Japan Trench and Nankai Trough off the coast of Japan. Four students from the University of Innsbruck have the unique opportunity to join Univ. Prof. Michael Strasser and Dr. Jasper Moernaut from the Institute of Geology on their ocean research project. The cruise investigates the causes and consequences of earthquakes and tsunamis. Every week of the cruise a blog is written reporting on both research and daily life adventures on board German research vessel Sonne.


ROV is lowered into water (Credit: Sebastian Trütner)

ROV Kiel PHOCA goes overboard. The container on the right hand side is where the pilots are operating the ROV. (Credit: Sebastian Trütner)

31 October 2016

After four weeks at sea our journey is nearing its end. The daily station plan, which informed everybody on the ship about upcoming research activities, only reads a single line today: 0700 Transit to Yokohama. Before we drift off into sentimental recaps, there’s still a lot of exciting science to be reported from week 4.

Since our pit stop in Yokohama we are accompanied by a team of technicians taking care of ROV Kiel PHOCA. This high-tech marine vehicle is about the size of a small car and can dive as deep as 3000 metres before the ambient pressure becomes too high for the PHOCA’s gaskets and valves. A 3 kilometres long cable supplies the motors and hydraulics of the ROV with power during its missions on the ocean floor. Seven HD cameras capture all movements from multiple angles and provide us with exciting live footage.

During a previous expedition to the Nankai Trough, some drilling sites have been equipped with monitoring instruments which need to be retrieved to acquire the recorded data. Not an easy task, given that we are floating two kilometres above these instruments on top of strong Kuroshio currents. This is where the years-long experience of PHOCA’s crew of technicians comes in handy.

ROV in action

PHOCA in action: a temperature probe is pushed into the soft sediment with the aid of an robotic arm. Easy for human hands, a tough nut for a robot.

Operating an ROV is an effort that requires two people who are fittingly referred to as ROV-pilots. Propellers, cameras and robotic arms need to work perfectly in-sync to complete even a simple task such as grabbing an object from the ocean floor. The level of skill required for such endeavours is very impressive: While the ship is being held in position with a maximum deviation of a meter, some 2 kilometers below the ROV must find a drill hole with the diameter of a can of coke, undo the water tight sealing, carefully pull the instruments from the casing and proceed to bring them back to the surface safe and sound. Facing such efforts, we begin to understand why it has been said that we know less about the bottom of the oceans than we do about the surface of the moon.

Angry local
The locals – understandably - are not amused by the unlikely intruder.

We’re lucky to look back at four incredibly exciting and fascinating weeks. During this expedition, we travelled a total distance of over 6000 kilometres, recovered 112 metres of sediment cores, surveyed about 4500 kilometres of subsurface profiles, mapped well over 10.000 square kilometres of ocean floor and generated 496 GB of data. Now we finally can catch some well-deserved sleep before we start lab work back in Innsbruck. A frighteningly large pile of samples anxiously wants to be analysed. We’re curious about what we may learn from the results and what kind of secrets await discovery inside the mud.

 

Sayonara Japan, Griass di Innsbruck!

Paul, Jana, Domi, Toby

 


Geochemistry (Fujiwara)
The pore water is taken from the cores (Credit: Toshiya Fujiwara)

24 October 2016

And another week passed on the Pacific! Since we last wrote, we arrived safely back ‘home’ in Yokohama harbour. Sadly, we had to say goodbye to part of the scientists of the first leg. Aside from the goodbyes we also had the chance to discover a bit of Japan during the three days in Yokohama harbour. One of our Japanese colleagues was so nice to be our tour guide for a few days and showed us Tokyo, temples and of course typical Japanese food. A good preparation for another two weeks on Sonne.

Our new research area is called the Nankai Trough and is located southeast of Japan’s main island Honshu. Here, the Philippine Sea Plate dives under the Eurasian Plate, forming an active subduction zone. This makes earthquakes a common phenomenon in the Nankai Trough. More examples of the force of nature can be found under the calm surface of the ocean: The area is densely covered by mudvolcanoes. They are structures that spit out hot mud and gasses from deep below.  Sediment is fed to the area through deep underwater canyons. These canyons bring down fresh sediment during earthquakes which results in beautiful stratigraphic sequences seen in the sediment cores. You can almost read the cores like a book!

Geotechnics lab
The geotechnics lab: The sediment undergoes several tests to determine physical properties (Credit: Tobias Schwestermann)

In our previous blogs we talked about the process of recovering sediment from the seafloor and how to map the underwater topography. But what does actually happen to a core when it comes on deck and how do you read the story this mud has to tell? There are three labs on board which analyse the cores: The geochemistry, the geotechnics and the sedimentology lab. Each one of them has its special task in investigating the sediment. After a core is brought on deck, the geochemists are the first to take their samples using syringes to suck out pore water from the core. They take this water and run different tests to determine the chemical composition of the water. Next, the core is split lengthwise into the working half and the archive half.

The working half goes to the geotechnical lab where they test the sediments physical properties. The geotechnicians run several analyses with all kinds of equipment that fall and rotate into the sediment. Leaving this laboratory, the core looks quite similar to Swiss cheese.

Inspecting the sediment
Michael Strasser inspects a new sediment core 
(Credit: Sebastian Trütner)

The archive half is the one that is brought to the sedimentologists. This half is treated with great care as it is later stored in the core repository in Bremen. The sedimentologists take pictures and describe the core in every detail as even the slightest color change may help to unravel more of the secrets earthquakes and tsunamis still hold. Not only the way a core looks, but also the smell can tell more about the environment of deposition. The occasional smell of rotten egg coming from the cores says a lot about the chemical environment and biological activity. Sometimes the sediment is even ‘tasted’ to test the grainsize of the mud. Almost all senses are used to read this book!

When all analyses have been done the three labs come together and talk about their findings. All data is combined and discussed. It sometimes feels a bit like playing detective.

The time on RV Sonne passes by quickly. Hard to believe that in a little over a week we will be back in Innsbruck again. Though, until then there is still a lot to do! In our upcoming blog we will report about the exiting dives of the underwater robot Kiel PHOCA which will bring us pictures from over 2000 metres waterdepth.  

 

Jana, Domi, Paul and Toby

 


Back to Yokohama
On our way back to Yokohama - amazing cloud formations are drawn in the sky by the autumn winds (Credit: Sebastian Trütner)

17 October 2016

The second week of the cruise passed by and so it is time for another update from the RV Sonne. Right now we are on our long way back from the research area to Yokohama harbour. Sadly, a part of the team will leave us there to return back to their working desks at home. For the next leg of our expedition their rooms will be taken over by the specialists of the ROV Kiel PHOCA.

The last week proved to be very productive as we managed to recover over 90 meters of core from the seafloor. The first data looks promising and we have been able to check all the ticks of the ambitious plan our chief scientist Michael Strasser had prepared for the Japan Trench.

Before taking a sediment core the seafloors topography – or bathymetry – is mapped in detail using a Multibeam Echo Sounders (MBES). This equipment sends high-frequency acoustic waves which are reflected by the seafloor then measured on board and converted to depths.

Hydroacoustics Lab
24 hour watch in the hydroacoustic lab (Credit: Tobias Schwestermann)

Along with the MBES, a so-called Sub-Bottom Profiler (SBP) is used to investigate the ocean floor. The functioning of this instrument is also based on acoustic signals, though on ones with a lower frequency. These waves can penetrate the seafloor up to 150 metres depth and bring forth a lot of information about the structure of the sediment.

During the last weeks we extensively mapped an amazing 2038 kilometres of the Japan Trench. This meant hard work for the guys and girls of the hydroacoustics team, but the 24 hour shifts are absolutely worth it: No other research vessel worldwide has open-ocean mapping capabilities as powerful as RV Sonne. Our mapping tracks therefore result in very exact bathymetry maps on which sediment movement can be traced precisely.

Little Bird on deck
(Credit: Yukihiko Nakano)

While the geophysicists were working hard in their window-less control centre the other labs had an unlikely visitor. A little bird, blown away from land onto open sea by typhoon Chaba, suddenly appeared on deck. An unusual sight when 200 kilometres off coast!

 

Paul, Toby, Domi, Jana

 

 

 


piston corer
The piston corer in action (Credit: Sebastian Trütner)

10 October 2016

It’s time for a quick update from RV Sonne! We luckily managed to stay out of typhoon Chaba for the most part. We did, however, catch some impressive waves that were left in the aftermath of the storm. Other than that, conditions have been treating us quite well lately, and we occasionally get to enjoy a little sunshine on deck.

Starting from Yokohama last Tuesday, we have been working our way up north along the Japan Trench. The Japan Trench is oriented roughly north-south, at a distance of 150 to 200 km to Japan’s eastern shore. One of the goals of this cruise is the retrieval of sediment samples from depths of up to 8 km below sea level (just to put that in perspective: if a mountain twice the size of Großglockner, Austria’s highest peak, were located at this point, its highest point would still be 400 m under water). This, of course, is no simple task: depending on the desired core length, a five or ten-meter metal tube is fitted with massive lead elements (1100 kg) at its top end. The force of these weights will allow the coring device to deeply penetrate the sea floor. The inside of the metal tube is fitted with plastic tubing, the liner, which will capture the sediment during the coring process. Shortly before touchdown on the seafloor, an intricate mechanism releases the corer, which will then free-fall into the ocean floor, thus allowing for greater penetration depth. Simultaneously, a piston moving up the liner creates a vacuum at the top that further helps sediment recovery (hence the name piston coring). Immediately afterwards, the coring device is winched back up to the ship. This may take several hours, depending on water depth. Once back on deck, the now sediment-filled liner is removed from the metal tubing, cut into segments of one meter, and meticulously labeled. Then, our geochemistry team takes pore water samples. Lastly, cores are cut lengthwise to produce to halves: the archive half, that we photograph and log, and the working half, from which samples are taken. The working half is also available for further investigation in one of the many laboratories on RV Sonne. Stay tuned to learn more about our onboard lab work!

 

Domi, Jana, Toby, Paul

 


EAGER Locations
The research locations in the Japan Trench and Nankai Trough

4 October 2016 

In 2011, Japan was struck by a magnitude 9 earthquake that became known as the Tohoku earthquake. The tsunami that followed destroyed and disrupted large areas of the coast causing both great human and economic losses. Japan is located at the southeastern part of the Eurasian Plate where both the Pacific and Philippine Sea Plate dive under, forming two of the world’s most interesting and active subduction systems: The Japan Trench in the northeast and the Nankai Trough southwest of Japan. Due to Japans vicinity to these two plate boundaries, earthquakes are a very common phenomenon. Therefore, many research cruises have investigated the sea- and subseafloor to search for valuable clues in the mud deposited on the ocean floor. Despite advancements in our understanding of both earthquake and tsunami hazard, unresolved problems remain.

From the 4th of October to the 2nd of November we will join a multidisciplinary research team on board the German research vessel Sonne. Together with 29 participants from 11 nations, we will set sail to the Japan Trench to investigate the geological impact of the 2011 Tohoku Earthquake by mapping the seafloor and sampling sediment cores. The second leg of the cruise will take place in the Nankai Trough where monitoring equipment deployed in the subseafloor during a previous cruise will be retrieved by a remotely operated vehicle (ROV) and analysed for earthquakes signals.

Group picture
from left to right: Paul Töchterle, Tobias Schwestermann, Jana Molenaar, Michael Strasser, Dominik Jaeger and Jasper Moernaut

During the next four weeks, us Innsbruck students at sea, will write a blog about the research as well as the daily life on board. Right now we are in the harbour of Yokohama preparing for departure. We are about to leave for our first open ocean research experience. Even though a typhoon is on the way (and is expected to go straight through our research area), spirits are high and everybody is motivated to sail out! We are looking forward to adventure and great science. One of us will keep you posted every week right here.

 

Sayonara!

 

Jana Molenaar, Dominik Jaeger, Tobias Schwestermann and Paul Töchterle

 

 

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