13 June - Two years down, one hour up

Today we had a departure from the frenzied CTD’ing that has dominated the cruise so far as we started retrieving bits of kit that had been moored in the North Atlantic for the last 2 years.  The moorings have various sensors to measure temperature, salinity and current speed, as well as large yellow plastic cones called sediment traps which collect material that has settled out from the surface layers of the ocean.  Retrieving moorings at sea is often a fraught business. After the ship has returned to the area of deployment an acoustic signal is sent out which is basically a ‘hello’ to the mooring.

The mooring, if behaving, replies with it own acoustic ‘hello’. Once electrical greetings have been exchanged, a different acoustic signal is sent out which releases the mooring wire together with the attached sensors, sediment trap and flotation spheres from its anchor.  You then wait for the sighting of a small yellow or orange buoy somewhere within a half mile radius of the ship. Sometimes there is no return ‘hello’, sometimes it returns a hello but doesn’t release and sometimes it comes up with fewer items than it went down with. But occasionally it works and so far we have recovered three out of three moorings with a fourth on its way.

Assuming this mooring retrieval business goes according to plan we’ll be resuming play along the extended Ellett Line transect by tomorrow afternoon and the happy sample collecting dance that takes place around the CTD that invariably involves hard hats and silicon rubber tubing will continue. Can’t wait…

CTD does not stand for Collecting Tube Device but it should do.

Tim Brand, SAMS