Last Summer , I took part in the most wonderful adventure of my scientific life (so far!) , two back-to-back cruises on a hydrothermal field located on the Mid-Atlantic Ridge (where the oceanic tectonic plates are formed and go apart). This field is the very well known TAG Hydrothermal Field.
Photo: location of the TAG Hydrothermal Field on the Mid-Atlantic Ridge at 26 degrees North. (Google Earth credit)
The first cruise was on board a German ship, the Meteor. The second cruise was on board the James Cook, the oceanographic ship based at the National Oceanography Centre of Southampton. The two cruises are involved in the project Blue Mining, an European Commission funded program (www.bluemining.eu) which aims to provide breakthrough solutions for sustainable deep sea mining.
Photos: The two ships. On the left, the Meteor docked in Barbados, on the right the James Cook docked in the Azores. (Iain Stobbs credit).
My colleague Iain Stobbs summarizes the cruise in his own words and explains his PhD project. I let him speak:
“My PhD research is focused on deep sea mineral deposits known as seafloor massive sulphide (SMS) deposits, these deposits form a result of ‘hydrothermal’ fluids moving through the oceanic crust, scavenging metals from the crust and then depositing them in mounds on the seafloor when they seep into the ocean. “
“Often one of the most important parts of geology research is fieldwork, when the rocks you are looking at are on land, it’s relatively simple to organise and you can go look at them in person. However, as a geology PhD student who is looking at rocks which are below the seafloor and under 3,500 m of water, it makes things a bit tricky! That’s why going on research vessels is a fantastic opportunity to get as close as possible to our main areas of interest.”
“Both of the cruises had different aims and different equipment in use, the first cruise, M127 was focused on ‘exploration’, essentially trying to develop techniques to image and find these extinct SMS deposits which are difficult to find in comparison to the active systems. The second cruise, JC138 was focused more on interpreting the geology and drilling of these extinct deposits. “
“My main role on the M127 cruise was helping my fellow NOC PhD student Adeline Dutrieux with the gravity coring operations. Each gravity core operation took approximately 3 hours and it was only once the corer was back on deck that we found out whether it was a successful core.”
Photo: A scientist hold the gravity coring device before being released. The device consists in a 500 kg head and a long 3-m liner. By gravity, it will dip into the sediments at 3500 m in depth. These sediments will be kept inside the liner until back on deck. (Adeline Dutrieux credit).
“Once the core was extracted from the corer we cut them into 1m sections and transported them to the cold laboratory, kept at around 4°C to mimic bottom ocean temperatures. Processing of each core was would often take several hours. In the cold lab, we extracted the pore waters.”
Photo: Cold in the cold lab while I, Adeline, am currently extracting the pore fluids from the cores with a syringe! (Adeline Dutrieux credit).
Photos: On the left, two scientists (Adeline and Sofia) take care of the cores. They split it in two before subsampling and photographing. On the right, what an example of the cores! It has a very changeable lithology (different material). (Iain Stobbs credit).
“Then it would be split and described before the sediments were further subsampled, photographed and then stored. We often attempted 3 or 4 cores in a row and operated overnight which fitted in well with the other operations being conducted throughout the cruise.”
As Iain said earlier, the main aim for the Meteor cruise was the ‘exploration’. A AUV (Automated underwater vehicle) called Abyss did several dives to realise a very high resolution bathymetry map of the field. During her 10 hours dives, she collected depth measurement but also magnetic data and self-potential data. On board, the scientists processed these data and brought us a new view of the bathymetry. We could distinguish a difference of depth of two objects at 50 cm apart!
Photo: Abyss is launched from the back of the ship at night for a 12 hours dive. On the right, a high resolution bathymetry map of the area of interest. The purple colours express the deepest environment. (Adeline Dutrieux/Iain Stobbs credit)
Photo: Abyss waiting for her recovery on deck. (Photo: Adeline credit).
Also, we virtually dived with HyBIS. HyBIS is for Hydraulic Benthic Interactive Sampler. It is a simple quite already technological robot-like instrument. It can dive up to 5000 meters-depth and can collect samples from the seafloor. On the Meteor, the HyBIS was equipped with a shovel who collected mud, sediments and oxides fragments. The main purpose of this action was to recognise other inactive hydrothermal mounds. We did find a large one, particularly promising and called it Rona Mound in honour to Peter Rona who spend long years of his life working on the TAG Hydrothermal Field.
Photos: On the left, HyBIS comes back on deck with his shovel full of mud. On the right, the scientists Sven Petersen and John Jamieson collect the mud delivered by HyBIS. (Adeline Dutrieux credit).
Photo: Here are the few oxide crusts being washed. (Adeline Dutrieux credit).
Photo: “My view of the early morning sky while manning a test of the parasound, an instrument which can provide information of the amount of sediment cover on the seafloor.” On the left, every two or three days, if the weather permitted (not too hot and not too windy), we entertained ourselves by doing work out in the evening. We must keep fit while we are stuck in a narrow environment. (Iain Stobbs credit).
“After a 10 day break in the Azores we were ready to set off on the James Cook for JC138. A main difference between British and German cruises is that the British cruises often operate on a shift system, compared to the German approach of ‘work when needed’. Therefore we sorted out shifts and split the geological team so that we could theoretically work for 24 hours solid between us. My main roles on the JC138 were to log, photograph and document the recovered drill core and to undertake interpretation and geological mapping of extinct mound using video footage obtained from our HyBIS (Hydraulic Benthic Interactive Sampler) remotely operated vehicle, which also collected a few surface samples. Ultimately the intensity of work associated with my logging role was dictated by the success of the rock drilling, which encountered a wide range of problems across the cruise. This shows the difficulties with conducting research in these extreme environments, however, by the end of the cruise almost all of the problems encountered were overcome enabling recovery of core material from three different extinct SMS deposits.”
Photo: The main lab is home of the HyBIS control. We have three cameras set up on HyBIS and two technician control the action of the propellers as well the length of the cable out to move HyBIS in any direction. (Adeline Dutrieux credit).
Photo: The Rock drill (RD2) belonging to BGS (British Geological Survey) comes back on deck after drilling sometimes up to 48 hours non stop on the seafloor. (Adeline Dutrieux credit).
“Our main findings from the drilling campaign was that at all three drilled mounds, the same sequence of rocks was recovered, this include a very hard, possibly relatively impermeable layer of silica and iron rich rock. This layer was directly overlying the massive sulphide minerals at depth, and is now one of the main focuses of my research.”
Photos: On the left, the core lab set up and ready to welcome any core from the rock drill. We see the core trays, the core splitter on the left, and a photography lab has been mounted in a corner. On the right, an inactive partially weathered sulphide chimney located on the edge of one of the extinct SMS deposits sutdied. The high quality of this image, obtained from the hyBIS HD camera, enabled mapping of the area. (Iain Stobbs credit)
Photo: Examples of the drilling cores. The top of the core is on the top left of the rack. It shows first a red rock rich in Fe and silica, followed by massive sulphide mainly consisting in pyrite and chalcopyrite.
“Now that I’m back ashore I can start with some of the more hand on side of my research, my sample have been cut and are being prepared to be made into thin sections. I can then look at these under a microscope and try and work out what minerals make up my samples. So once I know what my samples are made of, I can try and work out how they formed and then try to understand the processes that were ongoing to form these rocks.”
More detailed blogs written by our scientific crew over both cruises can be found on the project website (M127: http://www.bluemining.eu/researchcruiseblog/, JC138: http://www.bluemining.eu/research-cruise-2-james-cook-138/).