My first underwater movie

Two days ago, the multibeam team got excited during our CTD cast. They detected on their screen a particular water level with frantic activity, probably plankton and a school of fish, while Kate the marine mammal observer could not believe how many seals were around. At the end of the cast, we all commented on what a shame it was that we did not have a camera on the CTD. Except that we do have a camera, a torch and pressure/waterproof cases, but I had decided to wait until we were good enough at manoeuvring the CTD to install it. Funny coincidence: at the end of that same cast two days ago, Jari and I got cleared by Axel to work on our own. So yesterday was the day to start having fun!

Spoiler alert: I recorded the last two casts, and the videos are utterly boring. No crazy seal activity, bad light positioning, no size reference… But there were a few pretty good and/or funny moments:
1)      when the CTD hits the water

the last footage in the air (top), and 1s later (bottom)

the last footage in the air (top), and 1s later (bottom)

Actually, the whole sequence with the CTD being lowered in the water is quite cool to watch. It allows us to see the hull of the ship, and in particular the flushing system that is used to keep us clear of ice floes. But I save these images for a later post on how Oden breaks the ice. It also gives some kind of weird distorted mirror of the sea surface, especially on this image where we can see waves through various angles. In fact, in the bottom panel, you’re even looking through a wave!

2)      surface vs depth
We are now underwater, and all is blue-green-ish. That was to be expected. We see some unidentified living things floating around, some swimming past, and that was to be expected as well. And suddenly, the image turns black, and my first reaction is to think that my computer is having trouble. Then I realise that it is not totally black. There are bubbles at the front, and these are lit by the torch. We have simply reached the depths where the sun never shines.

surface blue, with some plankton (?) in the shade of the ship on the left, vs bottom black

surface blue, with some plankton (?) in the shade of the ship on the left, vs bottom black

I had another surprise while watching this video with the speakers on. There was a regular ping that could be heard when the camera was at the bottom. The thing is that when I watched this video today, I could hear a ping of the same rythm: the echosounder! Since a few hours after we joined the ship, there has always been a loud, regular ping. By measuring how quickly this ping comes back to the ship after having bounced on the sea floor, the multibeam team can work out how distant the sea floor is, and hence map the bathymetry of the area. And as soon as the ping is back, another one is emitted, so our ears are now tuned to it and we can tell how deep it is by listening to the frequency of the ping. That, as well, will be more detailed in a dedicated upcoming blogpost. I should also explain you why the ping can be heard best at the bottom, but hardly as the CTD was going down…

3)      our faces
The camera can only be switched on and off when it is out of its case, so each sequence starts and ends with our face. For the first cast, while we were trying to figure out how to make everything work, there is a lot of frowning and awkward-thinking-grins. At the end of the first cast, there might be a very short moment where the camera unexpectedly flies in the air while a comment in French starting with “oh m…” can be heard (the camera is fine). During the second cast, we were much better at setting it, so you can see us smile and laugh. Well, not entirely, because you can also tell it was much colder as our faces are less visible. But I shall leave you with this image of the case about to be closed. Next, I shall get muddy, watch the coring team work, and explain to you what I understood.

Special thanks to Katrien for the personalised hat

Special thanks to Katrien for the personalised hat


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