Starting over the side work – testing the kit and training the samplers

by Penny Holliday

Today marks a key day in the cruise – the start of over the side work. It’s taken us 3 days to get to the location where we want to work – just long enough for people to get used to the ship, but getting close the point at which some could get bored. But there is no time to be bored now – for the next 3 weeks we’ll be working hard to get everything done.

One of the first jobs on the cruise when we get out into deep water (~1000m) is to test our equipment and train up the people who will be collecting water samples for various analyses later on. This can be an exciting time with lots of people watching and taking photos, and a busy time as first-timers have a lot of information to take in, and experienced folk brush up on their skills.

The equipment in the picture below shows the instruments that make up our "CTD" and instruments that will be attached to our moorings. This whole package is lowered to just above the seabed to record data about the water it passes through. The instruments arranged in the lower part of the frame record temperature, salinity, pressure, oxygen, fluorescence (indication of algae in the water), transmittance (indication of concentration of particles in the water) and velocity.

When the CTD is close to the seafloor (10m above it), we start closing those vertical grey bottles on the frame. There are 16 in all on it at the moment (24 when it is full) and every so often we stop upward progress of the CTD and close a bottle by sending a signal down the cable. When it comes back on deck we draw off some water from each bottle that we’ll analyse for salinity, dissolved oxygen, nutrients, carbon and some isotopes. All of these things will eventually help us understand the role of the ocean in the oxygen, carbon and nutrient cycles of the planet.

Our first test was a shakedown CTD cast to make sure the main instruments work OK (they did!). The second was to test the self-contained mooring instruments (silver with red tape arranged vertically between bottles) and to collect data for calibrating them before they are left underwater for 18 months. I’m very pleased with the way things have gone today.

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