Thursday, March 22, 2012

CTD's and DIC's!!

One of the jobs I had on the Tangaroa was to collect water from the CTD instrument for Kim Curry down at Dunedin. There were 2 samples I had to take from different depths and Kim will be running CTD and DIC tests from these. A CTD — Conductivity, Temperature, and Depth — determines the main physical properties of sea water. It gives scientists a precise and comprehensive charting of the distribution and variation of water temperature, salinity, and density that helps to understand how the oceans affect life. A DIC --  Dissolved Inorganic Carbon Profiles -- was the other.
CTD coming back up
The CTD was lowered over the side and sent to the bottom. Then, on its way back up the water column, Nikki told a crewman to stop and start it at different depths and she, using her laptop in a lab, sent the instrument an electronic signal to collect a water sample in a bottle mounted on the instrument's cages.  
Once the CTD was back on deck, Nikki put tags on the bottles, informing us the depths and which ones we could take water from. Different people were taking the water for different tests.  Sometimes another scientist would have their name on the same container, other times I was on my own. For each water depth, I had a plastic 1 litre bottle and a smaller glass (400ml?) bottle. 1st I attached a plastic tube to the bottom of my water supply.  There is a plug at the bottom you push in once the plastic tubing is on. The actual tap though is at the top. I put a little of the water in my bottle, swished it around and poured it over the cap.
Taking a water sample- interesting temperature variation at different places.
Did this 3 times to wash out the bottle. Then filled it, taking care not to get air bubbles in it. With the 1 litre plastic bottles, I had to leave a 5ml (1 teaspoon) gap at the top. This was tricky sometimes because it is easy to squeeze the bottle! The glass ones had to be filled, then keep filling for 1 ½ times. (overflowing) The way to do this was to fill the bottle, counting up to say 20, then let the water overflow, counting another 20, then 10. Just before I put the cap back on I had to tip a bit out (1cm gap at top)
The levels for memory were 3000m, 2500, 2000, 1500, 1000, 750, 500, 300, 200, 175, 150, 125, 100, 75, 50, 40, 30, 20, 10m. These were done over two drops. The 1st being the deep water then the top 10.
Once done, we had to put poison in the bottles to kill off any thing! Mercuric chloride. HgCl₂
Very carefully done in a lab with a fume vent, special rubber gloves, and plastic glasses to protect your eyes. Scott put 2 drops into each bottle while I screwed them up tight. I’m going to be doing this next time- yikes!

Carefully adding HgCl₂in lab

Finally we put a paraffin tape around each bottle to seal them. They will all go to Kim Curry to work on.
I did the 2nd lot of filling all by myself which was cool. Scott must have thought I was doing an ok job to leave me to it!

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