Wednesday 16th June 2010

We arrived at the SW station at 3.30am this morning. As with every station, the first job was to deploy the CTD, then to recover the mooring line. We were a bit worried that we might have problems finding the mooring line on the surface as there was dense fog all around. The best way to locate the mooring line when it has surfaced is to look out for the orange flag that is mounted at the top. Luckily, the fog began to disperse in time and the mooring was easily found. The fog dispersed so much in fact that it turned into quite a sunny day… yay! A few of us even grabbed a short sunbathing session out on the forecastle deck, at the front of the ship. Meanwhile, the ROV was deployed for a video survey of the slopes and flat areas.

But, I had another mission… to build a new ‘observation tool’… in all honesty, this mission was born out of a bit of desperation, but will hopefully turn out to be very useful! There’s an important thing to accept when you do deep sea science: you might not get all the data that you planned to get. This is particularly true of deep sea science because you only have a limited time to do what you need to do, and if the weather or your instruments (or your whale bones) fail to co-operate you probably won’t get another chance. So, you have to be resourceful and take full advantage of what is possible when other options may not be possible.

The new ‘quadrat with light box’ - codename HALO

 Getting back to my mission… I am on this cruise to study the deep-sea bioluminescence at the Mid Atlantic Ridge. One focus of my studies is bioluminescent fauna (animals) in the water column. In deep waters, below 500 m, there are estimates that up to 90% of the animals are bioluminescent. These include swimming animals (nekton) such as fish and squid, as well as slower moving animals (zooplankton) such as crustaceans including shrimp, amphipods and ostracods, as well as gelatinous animals like medusa, ctenophores and siphonophores. I measure the abundance of bioluminescent zooplankton using the ICDeep profiler. The ICDeep is an ultra sensitive video camera that is mounted on the CTD frame, focussed downwards onto a rectangular mesh. As the CTD moves down from the surface to the seafloor, the zooplankton in that column of water are stimulated to bioluminesce as they impact on or pass through the mesh (nekton can avoid the mesh). Then, from the video I can calculate the density of bioluminescent zooplankton from the surface to the seafloor. But on this cruise, with the ROV, I have also been able to adapt the system to study the abundance of bioluminescent zooplankton horizontally above the seafloor. This means I can study the distribution of bioluminescent animals at different heights above the seafloor at different sites on the Mid Atlantic Ridge. The ‘observation tool’ that I mentioned earlier, is part of this study and will enable me to get images of the animals and particles in the water above the seafloor. It is essentially a square frame (quadrat) that is moved horizontally through the water with a high definition camera filming everything that passes through it. But, if you use the big front lights of the ROV then it is nearly impossible to know what is passing through the screen and what is in the distance. So, to make sure that we only film the particles and animals that pass through the quadrat the only light that is used is a shaft of light shining across the quadrat area. This light comes from a box with a slot on the side of the quadrat. Hopefully, we can test it soon and see how well it works!

Fingers crossed,

Jessica Craig

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