D334: Monitoring ocean circulation in the Atlantic


Cruise diary

29 October 2008

Craig writes...

The ship is finally underway. We’re heading south-west out towards the site of two of our tallest moorings – ‘EB1’, and ‘EB2’ which stand in over 5 km of water and almost reaches the surface. You can see from the map (right) we’ve made good progress from the Canary Isles, but we’ve still got a little bit to go.

Life has become busy on board with everyone having settled in to their cabins and getting used to the daily (and nightly) bustle of the ship, and where to go for food, laundry etc. Before we get to the mooring locations, a lot of science work must be done onboard to ‘calibrate’ the sensors we’ll be putting on the new moorings. Most of the sensors we’ll be using are ‘microCats’ (see picture below).  These measure the salt content and the temperature of the water, which enables scientists to calculate the density of the sea water at different depths. If you know the density at different locations across the Atlantic you can then calculate the strength and the direction of the currents in between.

Location of RRS Discovery,  Wednesday 29 October
at lunch time – heading to mooring site EB1/EB2.

‘Calibration’ ensures that the sensors are recording accurately. To do this we attach microCats to the ships’ ‘CTD’ frame on the starboard (right-hand!) deck (see Picture 3). The frame is then lowered to the sea floor and back again and we compare the readings from the microCats to make sure they are functioning ok.  Last night we did two calibrations, the second coming up at 04:00am, with the night-watch on hand to download the readings and start checking the sensors.

A microCat sensor in the laboratory ready to go onto the CTD frame. The black nozzle at the end has a port to connect directly to a laptop to set up the sensor or download data.

The CTD Frame about to go into the water during the first of last night’s two calibration ‘dips’. John, the Discovery CTD Tech, is on hand to oversee the experiment.

We’ll do another one to test more of the sensors tonight – weather permitting. The sun is out but there’s a fair swell on the sea and a bit of a roll on the boat. Fingers crossed!

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