64PE376 - Dagboek 3 (in het Engels)

Physics Today!
Today we (at least some of us) start early, 5:30 local time. We want to place a lander right above the seep. The lander contains two Acoustic Doppler Current Profilers (ADCPs) and a microcat. The ADCPs are there to measure the current velocity and turbulence structure of the water column every 3 seconds and the microcat measures the temperature and the salinity every 5 seconds, which is effectively continuously, if you would ask any scientist on board other than the two physicists (me and Jurre). With the measurements we hope to establish the bubble rising speeds throughout a tidal cycle. Which means that the lander should be placed close, or even better still, on top of one of the bigger seeps, which is a challenge in itself. Moreover, there are several other constraints as the lander is connected to a weight with a 150 meter long cable and on top of this weight there is a 60 meter long cable hooked up to a surface buoy to pick it up later today. The weight and the buoy however are not to be placed within the east-west transect that we will do, today. So, we decided to place it to the North off the site.

Yesterday evening, Jurre and I had some problems programming the ADCPs, which was nicely captured by Dan on film... The fact that we got the problems solved (including hurrahs and high-fives) was not captured, however. Therefore, Dan asked us to re-enact that part for him to capture on film. According to Dan, we're not going to the Oscars, this year…
Before lowering the lander, I did a final check to hear whether they were pinging by plainly putting my ear on one of the transducers and listen and it was gently beeping - music to my ears. The actual deployment of the lander went really smooth, due to the experience of Marcel, Barry, Martin and Ger, while Joep was positioning the ship with millimeter precision on the bridge. Later today, the ROV will go there and take some footage of the lander in her new natural habitat.



Then the real program started at 6.30 with the morning CTD and most of the rest of the scientists appeared. The idea was to sample right above the lander. As I don't want the CTD frame landing on the lander, I restricted the total cast to 3 meters above the bottom, instead of the usual 1 to 1.5 meters. Hopefully, the lander will come out in good health, this evening.
The rest of the morning was occupied by doing quick CTD casts . And with quick, I mean quick even though all bottles would be closed. We wanted high resolution dissolved methane and nutrients concentration profiles, so the idea was to close the bottles on the way back immediately and about every three meters with the exact depth not really being of interest. Because the program capturing the data closes a bottle upon clicking on the button "Fire Bottle", I asked Jens, whether we CTD-operators were allowed to "Fire-at-Will" (unfortunately not).
This exercise led to an astonishing amount of 6 CTD casts with 15 closed bottles each, which had to be sampled by Dorien for nutrients, Piet for methane concentrations and Petra for methane isotopes. The actual sampling was done by Jens himself and I was asked to deliver the bottles from the wetlab to the CTD frame and back again to speed up the process. The sampling indeed went quick, now a huge amount of samples are waiting to be analyzed… That might take a bit longer than 2.5 hours.