Up CTD, down CTD

by Neill Mackay

For the last couple of days we have been on CTD watches which means that we work in 3 teams covering 8 hours each of a round-the-clock operation (which for this blogger means starting at 4am, and my first experience of darkness since leaving the UK as we have nearly 24 hours of daylight at this latitude!). Once we have arrived at the location of the first station, we make the CTD ready for deployment and then it is lowered into the water on a winch. We then issue instructions to the winch driver over the radio, telling them how far to lower the CTD on the way down, and giving them fair warning so that it does not hit the bottom! An early warning system in the form of a weight dangling down from the CTD hits the bottom first and sounds an alarm, making sure that we do not end up with a CTD covered in mud! On our shift the winch drivers coped particularly well with regular switches between instructions in English and Dutch, depending on which of us was on radio duty! On the way back up the CTD is stopped at intervals and the Niskin bottles closed one by one to collect the water samples. Finally the CTD is brought on deck and we take the samples for oxygen and salinity from the Niskin bottles, before making the CTD ready for the next station. And repeat!

Having completed the CTD stations, we now find ourselves back at the point where we recovered our first mooring, ready for redeployment. The mooring instruments are attached to the cable from the top down, starting with the smartie-shaped buoy we saw in the previous blog post. Then each sensor is added one by one, with the cable being paid out on a winch in between – a mixture of ‘microcats’ which measure temperature, salinity and pressure (a sort of mini-CTD), current meters, and thermistors which provide a backup for the temperature measurement. Finally the anchor – a large metal weight – is attached to the end of the cable and lifted over the back of the boat using a crane. A pin attached to a rope is used to release the anchor and *splash*, into the water it goes!

We have had a filmmaker on board during this cruise taking footage of our work. There is now a YouTube channel where you can find some clips he’s been making:



The CTD being lowered over the side


Disappearing into the depths!


Attaching some buoyancy to the mooring


 Mooring anchor about to be dropped into the water


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