by Neill Mackay
So after a quick turnaround in Reykjavik, leg 2 of the OSNAP cruise is now underway. A new science crew are on board – except for Loic and Colin who are in the unenviable position of knowing what’s going on, so have been answering all of our questions! After 2 days of transit in near-perfect weather we arrived this morning at the site of our first mooring. First the acoustic signal is sent to the release mechanism at the bottom of the mooring (see ‘How to catch a mooring’ earlier in this blog), and then the group exercise of staring into the distance looking for a small round orange object in a large expanse of blue ensues – the smartie-shaped buoy which floats at the top of the mooring. The spotting game took longer than usual as some rougher weather had arrived in time for the mooring recovery, which means that the buoy has to be spotted in the intervals when it reaches the crest of a wave before diving back out of sight. Eventually however it was spied from the bridge and we headed towards it to pick it up.
Alongside the recovery, servicing and redeployment of the moorings in the western half of the OSNAP east array on this cruise, we will be making CTD casts to gather some extra data (the CTD is explained in ‘Check check and triple check’ earlier in this blog, and you can see another picture below). For those of us new to the procedures, we had a run-down on how to make the CTD ready for deployment, how to monitor its progress as it goes down to the sea floor and comes back up again, and how to take samples once it is back on deck. On this leg of the cruise we will be taking samples of water from the Niskin bottles to measure nutrients and oxygen as well as the usual salinity used to cross-check the CTD sensor itself. Oxygen can be used as a tracer to learn about the history of the water at a particular depth – if the water sampled is high in oxygen this indicates that it originated at the surface where it absorbed oxygen from the atmosphere. Sampling the water for oxygen has to be done carefully using special sample bottles so that the samples are not contaminated with oxygen from the surrounding air.