70 out of 30

With the amount of scientist limited due to corona restrictions the work that can be done is also limited. Also, we had just 16 working days in the Labrador Sea despite being 5 weeks on board. These circumstances led to the prediction of just conducting 30 to maybe 40 CTDs during this cruise. At least that was the prediction on our first meeting nearly four weeks ago.

Nutrient sampling on one of the first CTD stations.
Photo: Conny Posern

Well, sometimes predictions are simply wrong. Yesterday we conducted our 70th CTD. For this time the reasons for the misprediction are quite easy to find and somehow nice reasons. We had a lot of luck with the weather and the sea allowing us to conduct measurements without any interruptions for 16 days straight. Besides, there were no major failures by any system, and everything went really smooth. So, we just went on and on with the measurements and ended up doing a lot more than we first hoped for.

  70 CTDs in 16 days also means the same procedure 70 times. Every time it went:

“Lab is ready. Winch, Lab, CTD into the water and to 10 metres”

“10 metres”

“And now to 22 metres”

“22 metres”

“Then, back to the surface and start lowering with 0.5 metres per seconds”

Then it took between 5 minutes and 3 hours, depending on the depth, before the instrument came back on deck and we could start the sampling of oxygen, nutrients and salinity samples. The correct ways of how-to sample are well known by now. As teachers like to say: “If I wake you up in the middle of the night you still should know it”. We surely proofed this sentence right for our case.
Conducting way more CTDs than we first thought brought some issues with it. Our chemist was running out of containers for contaminated liquids, but the crew could find a few so we did not need to reduce our oxygen samples. For the nutrients that was the case, as we found out that we didn’t have enough sampling containers with us. So, we reduced the number of samples towards the last CTDs. In the end we have taken the absolute maximum amount nutrient samples we could. One could call it an efficient use of our resources. 

The last CTD coming back on board in the afternoon sun.
Photo: Daniel Rudloff

And still the number 70 was something special on this cruise. It was the final one. For the last time on this cruise we brought the CTD to 3600m depth and up. Just in time the sun came out to give us a little bit of a ‘the work is done’ feeling. Which is not entirely true, but the data acquisition is done for the cruise. From now on we focus on processing the data we have collected so far. Curios as we are, we conducted a little experiment with a can of an American soft drink company and found out that it does not not break under the pressure of 3600 dbar and is refreshing afterwards.

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