Studying oceanic crust: geology on board a research vessel


In December 2014, the brand new R/V Sonne departed Las Palmas, Gran Canaria to traverse the Atlantic Ocean. For 6-weeks the goal was to map, sample, and explore off-axis ocean crust. A team of geologists, biologists, and oceanographers were on board to make this voyage as successful and productive as possible. The ship runs on 24-hour work schedule; at any time a scientist on board will be busily working on collecting data, be it samples of deep-sea crustaceans or measurements of water column turbidity.

During the cruise bathymetric maps were produced using multibeam sonar surveys. These maps provide high-resolution images of the seafloor and help us understand how it evolves through time. We were able to observe underwater channels, faults, core complexes, and scarps (which are just a few of the structures visible on these maps). In addition to mapping, samples of sediment were collected using a gravity core (a large metal tube with weight at one end that collects up to 5 meters of sediment), MAPRs (Miniature Autonomous Plume Recorders) were in search of hydrothermal plumes, and an AUV (Autonomous Underwater Vehicle) was deployed to collect backscatter data and photograph details of the seafloor.

I was involved in dredging for samples of ocean crust. We were interested in how the composition and alteration of ocean crust changes through time. So we collected samples at specific locations with respect to the distance from the Mid-Atlantic Ridge. To dredge the ocean crust we used a chain bag dredge. Like it sounds, it is a large metal bag that is deployed and dragged along the surface of the seafloor. To avoid sediments that have accumulated on the seafloor and use gravity to encourage samples to fall into the bag we look for steep cliffs to dredge (greater than 20° is ideal). On this cruise samples were collected at a water depth, on average, of 5000 m and the time to complete a single dredge was approximately 6 hours. Rocks collected include basalt, gabbro, serpentinite, Mn-crust, Mn-nodules, and mudstone. Although the dredge can sometimes return to the ship empty, we were lucky to collect lots of samples. Rocks that were successfully recovered were examined and catalogued on board the ship, and have now been brought back to land so specialists in the field can study the samples in detail.

Although science is the focus of all research cruises, we can’t deny that we have a lot of fun both while we work and during our time off. Being a brand new ship, the R/V Sonne felt like a luxury cruise. Everything was shiny and clean, the food was top notch, and the amenities were plentiful. Whether we were playing table tennis, or watching a movie, we never felt out of touch or hard done by. This particular cruise was over Christmas and New Year’s, which can be difficult, but everyone on board stuck together and formed a temporary family. Although it may not be what we were used to, it was still a pretty magical Christmas (and the fact that it was 25 degrees and sunny certainly helped lift our spirits).

Khalhela Zoeller is a PhD Candidate in Economic Geology at the University of Ottawa; currently studying the distribution of base metals in oceanic crust.

Photo credit: Thomas Walter.

Views expressed in blog posts reflect those of the author, and not necessarily those of the CFES.

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