Saturday, 26 July 2014

The Mid-Atlantic Ridge

At the northern end of our travels we are looking at the Bear Island Fan. This is one of the largest packages of fan sediments in the world. It extends from the continental shelf just south of Bear Island westwards to the Mid-Atlantic Ridge (MAR). We wanted to see if any of the debris flows that make up the fan reach the centre of the MAR. This gave us an opportunity to survey along this dramatic structure to see if there was a suitable site to sample. First as we approached the ridge we could see on the 3.5kHz pinger records blocks of rock protruding through the well layered sediments. The multibeam showed that these blocks were parallel to the MAR and increasing in height and extent as we moved towards to the actual ridge.
Then we reached the ridge itself. As we steamed along its axis with Pelagia’s  starboard side above the European Plate and its port side above the American Plate the multibeam display was a confirmation of all those sketch diagrams on plate tectonics explaining the formation of oceanic crust at spreading centres, with each line of multibeam data added to the swath showed ridges parallel to the axis or evidence of volcanic activity. The ridge exhibits sudden large changes in bathymetry that makes following the seabed on the 3.5kHz pinger involve frequent changes of the display offset. It showed the rocky seafloor but we could see no thick sequences of sediments so we moved away to investigate the debris flows at the edge of the Bear Island Fan only a short distance to the east where we recovered a 10m long core with a very good record of the Bear Island Fan. 

Image from the Swath multibeam onboard the RV Pelagia of the Mid-Atlantic Ridge.
David Long

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