I have swapped blog days with Susan because I had hoped to once again write about the safety drill, but there was no drill. The marine crew certainly keep us on our toes. Who knows when the next safety drill will be? Matt, the chief-officer, informed me that when it happens the next drill will be about “situation awareness”, very intriguing.
We arrived at the northeast study site in the early hours of the morning (54° N 34° W). The sea was quite rough and the wind was blowing at 40 knots. We had planned to turn around a long-term seabed mooring, but the rough seas made this impossible. Instead the pelagic group from St Andrews University carried out an acoustic survey using the EK-60 scientific echosounder.
We started the EK-60 survey just after breakfast. The ship steamed up and down ten line transects, each was 8 nautical miles long, arranged in a grid design (shown in the plan-view picture below). Previously we carried out identical surveys at the other three stations.
Each of the 10 line transects is shown as a black line. The ship’s track is shown as a green line – the ship was about one-third of the way along line number two when the above screen shot was taken. Despite the rough conditions all the officers managed to steer the ship in a straight line along the transects. Matt (chief-officer) completed the best between-transect turn. He received top marks for a symmetrical turn that only took 6 minutes, instead of the usual 10.
During the EK-60 survey we detected some interesting acoustic scattering layers. Below there are two acoustic pictures, or echograms, from the 18 and 38 kHz transducer frequencies. There are between-acoustic frequency differences in the vertical structure of the layers caused by layers being formed by different zooplankton species.
In additional to the echosounder surveys we also collect samples from the water column using a rectangular mid-water trawl (RMT). The version the RMT that we are using has 6 nets that can be opened and closed remotely via underwater acoustic commands sent from an operator onboard the ship. The picture below shows the RMT being lowered into the water from the A-frame at the aft of the ship.
Unfortunately the electronics that control our pelagic net malfunctioned. The electronics are housed in waterproof tube, shown in the picture below, and are used to record the depth and speed of the net through the water and open and close the nets. The malfunction means that we are unable to open and close the nets. We are hopeful that with the help of Southampton based engineers, the Stig and Jon will be able to repair the net electronics.