At-sea testing and final development of the Hadal Water Column Profiler

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Very little is known about the mixing, circulation, chemical properties, and biological communities in the hadal water column, i.e., waters deeper than 6500 m. The handful of measurements that have been made show that rather than being quiescent and isolated from the ocean above, the water in the hadal zone is renewed on surprisingly short time scales. More multidisciplinary observations are needed to advance hadal water column science. To that end the researchers, using private foundation money, developed a 11 km depth rated (capable of getting to the deepest point in the ocean) Hadal Water Column Profiler which allows repeated vertical profiles of temperature, conductivity, dissolved oxygen, turbulent mixing, current velocity, acoustic backscatter, and video, and it has a small 11-bottle water sampler. The researchers conducted two days of at-sea testing which showed that the development had successfully produced a functioning profiler, but also that more at-sea testing is needed for the Hadal Water Column Profiler to reach its potential as a cutting-edge scientific instrument ready for oceanographic research expeditions. Once operational the Hadal Water Column Profiler will provide the means to substantially increase understanding of one of the most undersampled regions in the global ocean. It will enable the first direct measurements of turbulent mixing in the deep ocean trenches, allow for exploration of flow, trench ventilation mechanisms, and midwater biological communities shedding light on biological connectivity, and enable the identification of nepheloid layers created by turbidity flows that are likely common and important biogeochemically and biologically in trenches.This project will provide additional ship time for the final development of this unique instrument. During three 4-day periods of at-sea testing, the researchers will undertake six tasks identified from the prior at-sea testing. These tasks include optimizing the ‘flight’ characteristics for data quality and using contemporaneous traditional Conductivity-Temperature-Depth and Acoustic Doppler Current Profiler measurements to evaluate the data. During the previous at-sea testing a half size prototype water sampler was used. This project will allow a full-size water sampler to be tested. Finally, due to the unique capabilities of the Hadal Water Column Profiler, both in terms of depth rating and suite of sensors, future research expeditions are likely to rely heavily on this instrument so it is important to build up a documented history of performance in terms of reliability, data quality, and operational efficiency.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.