Ocean Bottom Seismology Days 11 and 12

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….And we’re back! Days 11 and 12 (18 and 19 July) are in the books with plenty of excitement, trials, and tribulations. When we last left each other, we had a line snap and a TRM crashing back to the seafloor. Jason and Medea were called into action and they were hot on the trail of retrieval. Well, Jason clipped on and the collection process began until a series of large swells got the best of our line again…. You guessed it…. SNAP! It’s an old sailor’s tale that the Pacific doesn’t give up her TRM’s when the skies of July turn gloomy. I guess that is Lake Superior not the Pacific, lives not TRM’s, and November not July, but you get the idea, she wasn’t letting go of FN09A quite yet. It would be another 24 hours before the seas would calm enough for us to return, but when they did, the day would belong to science.
It took some time and thought to arrive at the decision to abandon the last TRM, but focusing down track on other hurdles to clear was sage advice given by the team. We continued to J51A which was a pop-up variety OBS and easier to handle in 10-feet+ seas. Between the transit and the recovery procedure it soaked up a chunk of the day Wednesday, but we were able to grab the TRM at site J51A as well as conduct a CTD before making way to FN05A. A CTD entailed dropping a gauge into the water that measured temperature and salinity as a function of depth. I’ll now attempt to explain as best as possible why this information is important and hopefully get most of the details right…
When an OBS is dropped into the water, its clocks are synchronized to a master clock on board. Since there is no way to steadily update the time throughout the year, there is inevitably a variation by the time the instruments are retrieved a year later between the two clocks. The timing of seismic events between instruments is crucial to the accuracy of the data, so it’s vital that the differential be accounted for appropriately. To assume that the drift accumulated on a linear scale throughout the year (essentially taking the amount of variation and dividing it by the time it was down there) would be incorrect. There is a relationship (which I do not know the mathematical specifics of) that exists between drift and temperature. Each TRM is equipped with a temperature gauge so that a baseline data set can be obtained, but the gauges are brand new, so the CTD can provide a comparative figure for calibration of the data. OK, so that’s the best of my understanding and I have verified with Dr. Allen that I am not in left field, but don’t quote this in any official capacity because you’ll probably get torched for ambiguity.
Meanwhile, back at the ranch… we began our transit to FN05A which was rather lengthy. When we arrived we sent our release codes which were acknowledged and the buoy came to the surface but it wasn’t secured on deck without a hitch. When we were pulling the TRM onboard, the line tangled in the screw, a nightmare for any mariner. With the safety of our propeller uncertain, we continued on anyway because it was time to head back to our problem child at FN09A and get Jason in the water. Everything seemed alright after we were underway, Jason was going in the water to end our struggles at FN09A, and John and I were about to relieve the watch in the control van. Things were well. Within an hour we had found the instrument and began recovery efforts. The ordeal lasted four more hours, but we emerged victorious over the inanimate TRM and Mother Earth. TRM came onboard and was secured to the deck shortly after 0400 local time on Thursday.
Morale was high, wildlife leaped from their aqueous homes seemingly in exultation for our conquest, and the mission continued. We arrived at site FN10A around 0530 and had Jason back in the water by 0700 to retrieve another previously dropped TRM. When we arrived, we signaled a release which was acknowledged. Before long, the buoy was at the surface and retrieval began. We brought it on board, and this time it was without any issues… a welcomed site indeed. It’s a good thing too, because the rest of the day today was going to be a struggle.
Since that point, we went to sites FN06A, FN07A, FN19A, and FN01A of which only FN06A was recovered successfully. 07 acknowledged release code and never appeared at the surface as did 19. 01 was completely silent and unresponsive, which was a disconcerting return (or lack thereof) to say the least. So it’s going to be back to all of those sites with Jason to diagnose the problems and recover. Dreams of an early return are drowning under the weight of 1500-pound A-frames sitting at the bottom of the Pacific. All the while, I’m thinking about my Jambo family who today began rocking out in their tank tops and cut-offs at the Super Bowl of country music. For the next four days the biggest party of the summer will burn on, copious amounts of adult beverages and fried pickles will be consumed, and my guitar will gently weep to the sway of the mighty Pacific….. Until next time science fans.

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Comments

[anonymous]

You don't have to worry, Vogl called jambo "the Pro Bowl of country music" this year cuz the lineup was so bad.

[Buffalojunkie]

Hahaha
I don't know who made this comment (Baker?), but I thought the same thing when I saw the lineup. However, it would still be nice to be there!