Expedition 393 (South Atlantic Transect 2) is the last in a series of 4 expeditions in the middle of the South Atlantic. Occupying 4 of the 7 total sites, this expedition also provided an opportunity for repeated downhole activities that potentially captured temporal variations. This is on top of the rare site layout that transect the western flank of the Atlantic mid-oceanic ridge. Given this rare chance unique opportunity for a spatio-temporal coverage, a list of downhole activities were conducted during this expedition: the normal wireline logging, APCT-3 runs, CTD profiling and Niskin bottom water bottle sampling for microbiology.
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Given the derived sonic velocity (SV) from the CTD runs, different averaging techniques were also calculated and used as input in the Knudsen EchoSounder. Result from this single site show that the integral harmonic or arithmetic mean as defined by Maul and Bishop (year) provide the most accurate water depth estimate.
Niskin Water Sampling
The expedition microbiologists, Jessica Labonte (TAMU Galveston) and Shu Ying Wee (TAMU CS), requested that the Niskin bottle be deployed with the VIT in order to collect deep water samples that are closer in composition to what is circulated within the rocks, as compared to the surface water that was often used in the past. The closing mechanism designed during Expedition 391 was used and tested on deck, and was given approval by SIEM Electrical Supervisor that the 3D-printed PLA shear pin is of the proper strength to prevent stripping off the gear mechanism of the beacon release system. The previous mounting was modified by using a U-bolt to hold the bottle. The visual indicator for the release was made more discrete to the search camera view by using a clear nylon line with a rubber weight. The sequence of video still captures from the search camera shows the nylon lanyard across the lower right corner of the field of view, and how it swung out during the release.
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