Anouk Beniest is a PhD candidate at the University Pierre et Marie Curie in Paris, France. She works on continental rifting and break-up processes, with a focus on the South Atlantic domain. She got the chance to join a scientific cruise in the Indian Ocean on a German research vessel, ‘Sonne’, for the acquisition of seismic, magnetic and gravimetric data.
A warm, blue ocean stretches as far as the eye can see in all directions. The water is over 4000 meters deep, too deep for swimming. The weather is calm now, even for monsoon times, which is a good thing because I can adapt easily to the ocean’s motions. I am standing on the Monkey Island of a German research vessel, Sonne. The vessel left from the harbour of Colombo, Sri Lanka, and traces the 81o E longitude southwards. The empty quarter of the Indian Ocean lies right in front of me. The southern-most point of this trip is 11° 30´ S. The cruise will take me back and forth between the northern and southern hemispheres several times. On the other side of the ocean lies Antarctica that was once connected to India and Sri Lanka. The aim of the cruise is to understand more about the break-up history of Antarctica and so we trace back how India fled from Antarctica by gathering all types of geophysical data. As soon as we pass the nautical highway in front of Colombo deployment of the first equipment begins. The first acquisition instruments that need to be put into place are the magnetometer and the hydro-acoustic equipment.
While the magnetometer is recording and the hydroacoustic equipment produces high-frequency beeps, the ship is heading further south. We reach the equator and the weather is about to change. I am standing again on the Monkey Island, the highest deck on the ship where scientists are allowed to come. Dark clouds are rolling in and the wind is blowing so strong that I have the impression my eyelashes are blowing away. Despite the dark sky, the ocean still has its dark blue colour and suddenly a group of spinner dolphins turns up out of nowhere. There at least 30 of them as they jump out of the water, doing little tricks.
Clouds are covering the sky now and the waves have reached heights of over 5 meters. When on deck, the waves sometimes reach above me, which is very impressing. In the eating room the salt and pepper has been removed from the table as they wouldn’t stand straight anymore. In the lab everything rolls from left and right and front to back. It is time to learn some knots and secure all the equipment. The storm remains for a couple of days but there is no time to lose and so I prepare my first Ocean Bottom Seismometer (OBS) station while the ship is dancing with the waves. While I am testing my balancing skills I somehow manage to attach the different OBS equipment items to the brightly coloured floating devices. From time to time a wave floods the deck, making the whole scene quiet dynamic. My fellow scientist colleagues prepare the streamer and the airguns. The OBS stations and streamer will be deployed as soon as the longest magnetic profile is finished.
When the first OBS station, #301, is being assigned to the ocean bottom, all hands are on deck. Everybody is curious about the deployment procedure. To me, it is completely alien to throw heavily coloured equipment overboard and hope that they will surface again, but apparently this works. For two days and two nights I work my shifts to deploy all the stations. In the early morning of the second night, the last station is thrown into ocean. We watch a beautiful sunrise and treat ourselves on a well-earned cold drink. Then I go back to my cabin and dream about oceans full of floating OBS stations.
The morning shift deploys the airguns into the water. It is quiet a violent business as they are very heavy and bump against the back of the boat. The first seismic profile runs north-south and starts on the platform with only 400 meters water depth, close to the continent. It crosses the shelf to the deep ocean with roughly 4500 meters water depth. The shelf is the perfect area for marine wildlife and so the whale watchers have an intensive look-out to make sure no sea mammals are in the vicinity of the ship before the soft-start of the airguns begins. The shelf is also the perfect place to investigate how India broke apart from Antarctica as it records the whole break-up to spreading history.
The scientific team counts 26 people and during the data acquisition there are 4 hour watches day and night. Per watch, three people take care of quality control and airgun performance. In the meantime, we also prepare OBS recovery and the next seismic profile. But it’s not only work on the ship. There is some free time on board. For the sportive ones there is a gym, a table tennis table and a football table. There is also a library and a large television screen to watch movies. Even a sauna is installed complete with relaxing chairs on the sun deck. Every now and then there are events such as seminars given by the scientists, poker evenings, movie nights and birthday parties. Everybody is invited, both crew and scientists.
With five knots per hour, the vessel sails along the profile. At the end, it makes a turn and the recovery of the OBS stations starts. The whole OBS team is restless. Will the releaser pick up the signal and let go of the anchor? We wait for a long time, but then the bridge relieves us from our worries, the radio picked up a signal! The OBS station surfaced! The watchman has already spotted the device and the vessel heads towards the yellow, floating unit. On the deck the crew-members are ready to rescue the OBS station from the water using hooks and ropes. The recovery also continues night and day. My cabin is located on the second deck, close to the surface of the sea. I have bull’s eye windows and during the night I can see the OBS stations flashing by.
The recovery is going according to plan. OBS after OBS surfaces and gets safely back on the deck. The ocean remains blue and wavy. There is not much to disturb that few. Every now and then a lonely fisherman’s boat passes the ship, but other than it is quiet empty on this side of the world. The weeks pass by quickly. In total, we measured two seismic lines with OBS’s and streamer. We acquire 10 magnetic profiles and cover whatever we have sailed with bathymetry. Processing the data would be the logical next step, but most of this will be done back in our labs. The RV Sonne is used for many different research purposes and so the boat is not permanently equipped with OBS stations or a streamer. Packing all the equipment in containers, so the next cruise starts with a clean ship, is our last task before we get back to harbour of Colombo.
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