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TRASNA Blog – Day 5


TRASNA Blog – Day 5

Written by:

Peter Macintosh
Geologist
Undergraduate at Memorial University, Canada

May 16, 2016
Latitude 52° 24’
Longitude 31° 35’
1831 UTC
Wind SW@27knots
Air Temperature 9°C
Sea State 3m


We reached the Mid-Atlantic Ridge early this morning. The Mid-Atlantic Ridge is a diverging contact area between the Eurasian plate and the north American plate boundaries.  These areas are believed to be associated with magmatism formed by the pulling apart of the two plates.

The multi beam mapping system was working well throughout the night until this morning when the winds and waves began to pick up. The waves caused bubbles in the water column that creates interference with the multi beam. We decided to stop mapping until conditions improved which occurred later on in the day.

We then turned our focus to the major project of the day which consisted of dredging the Mid-Atlantic Ridge for rock samples. We use the dredger to collect rock samples from the seafloor so that we can have an indication of what types of rocks make up the seafloor and what processes may have created these rocks. The dredger that we use to collect rock samples from the sea floor is approximately one meter wide and one and a half meters long. The dredge resembles a basket with the bottom cut out and replaced with a metal net. The idea of this dredge is that rocks will be to too large to fall through the holes in the netting while smaller particles like sediment will be allowed to fall through the holes in the netting. To take a dredge sample we lower the dredge and drag it along the sea floor ideally collecting any lose rocks that are resting on the bottom.  Dredging is not always successful and is difficult because we are unable to see the area that we are dredging and do not know if there are lose rocks in the area or not. During our tests we were averaging 2 rock samples the size of a baseball per dredge.

 

Two crew members retrieving ocean dredge from sea floor

 

Rock samples retrieved during dredge

When we began dredging around noon we were dredging at 1800 meters. At this depth it takes an hour and a half to lower the dredge, drag it along the bottom and return it to the surface.

During our first dredge test we retrieved 3 rocks two of the samples resembled gabbro and one sample resembled dolerite.  During the rest of the day we conducted 6 dredges, two of the dredges were unsuccessful and one of the other dredges provided us with rocks that were highly weathered but initial observations indicated it could be calcite.  During the rest of our dredges we recovered a few rocks but all had similar characteristics to the initial dredged gabbro samples.