HR: 08:45h
AN: OS11C-04 INVITED     [Abstracts]
TI: A Fast Response Gas Tension Device for Use on Profiling Floats
AU: * McNeil, C L
EM: mcneil@gso.uri.edu
AF: University of Rhode Island, South Ferry Road, Narragansett, RI 02882 United States
AU: D'Asaro, E A
EM: dasaro@apl.washington.edu
AF: University of Washington, Applied Physics Lab, Seattle, WA 98105 United States
AU: Johnson, B D
EM: bjohnson@dal.ca
AF: Dalhousie University, Dept. of Oceanography, Halifax, NS B3J 4HS Canada
AB: We present the development and testing phase of a new fast-response gas tension device (GTD) designed specifically for use on an air-deployable, buoyancy adjustable, profiling float. The GTD measures total dissolved air pressure when equilibrated with the local waters through a gas permeable membrane. Dissolved N2 levels are calculated using gas tension, water temperature, salinity and dissolved O2. The new fast-response GTD maintains the existing GTD's high precision and accuracy (0.01 %) but provides a significantly faster response. The new design physically separates the existing GTD into two primary components, a membrane interface and a precision pressure sensor. The two components communicate remotely through a low dead-volume tube. This allows the existing GTD to be minaturized for incorporation on the float and allows use of a novel, water pumped, larger surface area, fast response membrane interface. The equilibration time of the new instrument varies with depth due to compression of the membrane and its associated reduction in gas pernmeability. This effect is found to be significant to a depth of 10-20 m. In addition, the large surface area of the new fast-response interface provides a significant hydro-static response to the GTD due to degassing of the air dissolved in the membrane when it compresses. These responses are however very repeatable allowing the raw GTD signal to be corrected. The new GTD design equilibrates fastest near the sea surface and has a minimum response time (e-folding) of around 2 minutes. We suspect this can be improved further. The response time at 50 m is around 10 minutes. The depth controllable float enables an optimal 'sample-and-hold' approach at specified depths to ensure complete equilibration of the GTD. This GTD-float package allows remote upper ocean dissolved O2/N2 profiles, and time series at specified depths, to be collected for use in air-sea gas exchange and net biological productivity studies.
DE: 4894 Instruments and techniques
DE: 4294 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting