[Cruise Journal: the rest of the cruise]
A busy time in which: Sentry successfully completes the remainder of its science dives; watchstanding and data processing continue apace; we begin sharing our already limited satellite internet with several other research vessels in the region; we wrap up our science mission and begin transiting to Guam; and all of the various books, computers, notes, devices, containers, coffee, and other accoutrements of marine geophysics in the field begin to be packed away for shipping back to their home labs.
As the surface towed maggie is retrieved for the last time, we can take stock of the status of the science mission and reflect on our time onboard during the few brief hours that remain.
The scientific highlight of the cruise has inarguably been the exemplary performance of the AUV Sentry in collecting magnetic data in close proximity to the Pacific JQZ ocean crust. Pushing the envelope of the vehicle’s operating depth and dive duration, the Sentry team have gone beyond the call of duty in enabling longer than expected survey tracks, squeezing the most out of the battery, and turning the vehicle around swiftly between dives.
In all, Sentry covered a total horizontal distance of 635 km over seven science dives. That near-bottom data is supplemented by 545 km of DeepTow track (197.9 hours of wire time, with 158.8 of that at data-collecting depth, and a maximum wire length of 5424 meters) and 7415 km of surface towed magnetometer data (that’s 4607 miles).
Being able to collect so much accurate data on the reversals and strength of the Earth’s magnetic field during this oldest portion of the Jurassic period for which ocean crust remains is a privilege. Past cruises in this research program have yielded data that are used in the canonical text on the geologic time scale (The Geologic Time Scale; Gradstein et al, 2012, Elsevier), and hopefully the data from this cruise will extend that tradition.
In the meantime, the watchstanding may have ended but a student’s duties are never done. Before arriving in Guam, remaining tasks include: packing personal effects; inventorying, packing, and triple checking lab equipment; making final data dumps and backups; returning linens to the designated repository; returning your stateroom to the spotless condition you found it in (brand new ship, remember); taking one last turn around the upper decks outside; and anything else you want to do on board before returning to shore.
All too soon after these things are completed, we’ll disembark from the Sikuliaq, which has become a comfortable and familiar second home, and say goodbye to the crew, who’ve been the consummate stewards, tutors, and travelling companions these past thirty days. With a vastly improved knowledge of marine magnetics, the shape and character of the Pacific Jurassic ocean crust, shipboard conduct and safety, echo-sounding sonars, Java archives for driving parametric sub-bottom profilers, euchre, and the tropical night sky, we’ll make our way toward further studies and travels. Sometime in the future, this program of exploratory research will return to the JQZ to finish up surveying the polarity reversals in the third side of that triangle of the world’s most ancient ocean crust — the Phoenix lineations to the south. Maybe we’ll see you there.
Thank you for joining us.