Collaborative Research: Quantitative Investigation of Finestructure and Internal Waves in the Norwegian Sea from Simultaneous Temperature and Acoustic Reflectance Measurements

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ABSTRACTOCE-0452744-0452265Oceanic finestructure can be imaged in great detail using low-frequency (10-150 Hz) seismic reflection profiling. In September 2003, a joint hydrographic/seismic imaging survey of oceanic finestructure was conducted, acquiring temperature and salinity data on 110 XBT.s and 12 XCTD.s as a low-cost piggyback to a previously scheduled seismic reflection study in the Norwegian Sea. Initial results showed that the reflection method (1) is sensitive to fine-scale temperature contrasts as small as 0.03 C; (2) can image finestructure from M2 internal tides and map the sites of M2 internal tide generation; (3) can map water-mass boundaries in great detail; (4) can produce quantitative internal wave spectra that reproduce the expected Garrett-Munk spectrum and deviations from it; and (5) can image disruptions in finestructure consistent with internal wave on critical continental slopes. This proposal will focus on analysis of the data, targeting the following questions: (1) How can we best extract quantitative information on internal wave displacement spectra and vertical coherence from acoustic images of finestructure? (2) What are the characteristics of the internal wave field in the thermocline of Norwegian Sea, and are there systematics with depth, distance from continental slope, and bottom topography? (3) Is high-wavenumber internal wave energy enhanced at sites near critical continental slopes? (4) Where are M2 internal tides generated on the Norwegian continental slope, and are there systematics with slope angle and tidal cycle? (5) What is the relationship of imaged reflectors to the geostrophic velocity field? (6) What is the shape of the deep water mass boundaries revealed in the various sections? This work is a logical next step in determining the capabilities and limitations of low-frequency acoustic imaging to study ocean structures and dynamics.