JC24: Dating volcanoes on the Mid-Atlantic Ridge


Cruise diary

Sunday 25 May 2008

We arrived at our work area just before breakfast this morning!  First order of the day was to lower a “sound velocity profiler”, which measures the speed of sound in water.  At the same time we attached a set of instruments called MAPRs to calibrate them.  They will later be deployed with TOBI and will use a number of sensors to detect the presence of plumes from hydrothermal vents.  This operation was complete by 11 am, when we started to deploy TOBI. 

We now had the first setback – on recovery from the SVP station, we found that some of the MAPRs were not working properly.  So we ended up putting two on TOBI, not the four we had planned.  Such are the difficulties of working in the oceans.

TOBI was fully deployed by 1230, then we turned in a slow circle to calibrate TOBI for the magnetic survey it will do.  TOBI continuously measures magnetic field, and we will use variations in the field as one way of estimating the ages of the rocks.  But the TOBI vehicle itself has a magnetic field (just as any lump of iron or steel is usually weakly magnetised), so by turning the vehicle we can measure the strength of TOBI’s field and hence correct for it.

We then had another hiccup, when we found that TOBI’s bathymetry (depth) signal on one side was not working well.  We then had to quickly redesign our survey so that the good side would be looking at the acial volcanic ridge (AVR).  Finally, by 1800 GMT we were able to start the survey in earnest.

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May 2008