Cruise Blog by Frances Cooke: Day 2
July 8th, 2021
Text and photo: Frances Cooke (PhD Candidate in the Gas Hydrates and Free Gas Reservoirs research group at CAGE, working within the SEAMSTRESS project).
Preparing the instrumentation
Temperatures have dropped and the skies are grey. The bathymetry (map of the seafloor) shows a typical Barents Sea display of iceberg ploughmarks cut deeply into the seafloor as we cross over the ‘Polar Sonen’ – a blue line displayed on the ship’s navigational map extending from Russia through to Iceland. We are still 1 day and 14 hours away from our OBS recovery site, but we have some tests to do along the way.
Barents Sea real time bathymetry swath with iceberg scours (yellow)
Preparation: OBS releasers
We are preparing our OBS releasers for testing at ~1250m water depth, away from the shallow Barents Sea continental shelf. It is important to test the instruments at the same water depth as the OBS site to ensure a comparable pressure. The releasers are the most important part of the OBS to test. If they do not function correctly, the OBS will fail to return to the surface. They are called back using an acoustic device that sends a command through the water to the instrument instructing its release. We will lower the cage with all six releasers (1 from CAGE (Seamstress) and 5 from AWI) and we will talk to them and wait to see if they talk back. Bergen University were lucky this year to recover their ‘lost’ OBS picked up during the AKMA CAGE cruise in May using a remotely operated vehicle.
The OBS releaser cage with two releasers inside (4 more left to prepare)
Top left: all releasers ready to be deployed (in view Kathi, Kunigunde and Kordula). Emma, Diana, Christine and Wojtek – the easily identifiable instrumentation from the Alfred Wegener Institute.
Five of the releasers have names: Kunigunde, Kathi, Kordula, Kaya and Kim. Vera and Machita inform us that all the parts that make up the OBS (hydrophones, frames, beacon, releaser etc.) have names. The names made for the releasers start with a letter K or L. In the labs at AWI, they have in total ~1000 pieces of equipment to manage, including auxillary parts such as laptops, deck units, and cables. They have 80 OBS equipment groups. Each OBS group is comprised of 10 parts. The serial numbers are so similar that naming the equipment makes it much easier to identify them. I ask how they manage to find names for 800+ OBS parts, and they reply that the names are both male and female, and both German and foreign. The names are also old fashioned such as Kunigunde. Watching the Denmark-England game last night was possibly as intense as the half hour wait time during the recovery of the OBS – at least for some. Others discussed the names of the players: Boleslaw – an old-fashioned Polish name. A good reserve name for a Beacon.
Top: The deployment of the releasers cage, bottom: Przymek, Vera and Mechita watching the winch wire go out, waiting for the cage to drop down to 1250m before communication with the releasers begins.
While Vera, Mechita and Przymek were preparing the OBS releasers, Truls and Stormer were preparing UiT’s two ‘Digi-birds.’ This is equipment used to control the depth of the cable in the water for seismic operations. The birds are mounted externally on a marine seismic streamer cable. They have acoustic devices that measure actual depth of the cable during operation, through an onboard sensor located in the wing module. Periodic adjustments are made to the angle of the birds wings (or “fins”) to drive the bird (and streamer) back towards the target depth.
Top: Truls and Stormer fix the wings to the birds; bottom: Truls and Stormer attach one of the birds to the streamer cable on deck.
Read more about the SEAMSTRESS project here.