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SUMMARY:SEISMIC ACOUSTIC IMAGES OF THE ANTARCTIC CIRCUMPOLAR CURRENT - K. 
 L. Sheen\, Department of Earth Sciences\, University of Cambridge\, Cambri
 dge
DTSTART:20100310T110000Z
DTEND:20100310T120000Z
UID:TALK23467@talks.cam.ac.uk
CONTACT:Zhaomin Wang
DESCRIPTION:Seismic oceanography is a novel technique of producing detaile
 d acoustic images of ocean finestructure. Here we present a series of ocea
 n seismic images from a region in the southwest Atlantic. Finestructure im
 aged in the data occurs dominantly along the Subantarctic Front and Polar 
 Front and at the boundary layer between Antarctic Intermediate Water and u
 nderlying Upper Circumpolar Deep Water. The images correlate well with pro
 ximal hydrographic data. One particularly striking image captures a km sca
 le overturning at the confluence between North Atlantic Deep Waters and ci
 rcumpolar waters and illustrates how water mass fronts can act as both bar
 riers and blenders to ocean mixing.\n\nTurbulent mixing rates in Drake Pas
 sage and the southwest Atlantic are known to be remarkably intense and wid
 espread. We have developed an automated technique to spectrally analyse in
 ternal wave undulations captured in the seismic images and deduce the spat
 ial distribution of mixing across seismic transects. Resultant seismic ref
 lection displacement spectra exhibit a continuum from internal wave type c
 haracteristics at low wavenumbers to more turbulent dominated motions at h
 igher wavenumbers. \nDeduced diapycnal mixing rates\, which although patch
 y\, are typically 10-4 m2s-1. Higher energy levels are found at the sides 
 of lenses of homogeneous waters\, regions of internal wave breaking and al
 ong rougher regions of seabed. A new technique of extracting cross-track g
 eostrophic current velocities from ocean seismic images will also be discu
 ssed. The method utilises the slopes of seismic reflections which act as p
 roxies for those of isopycnal surfaces.\n
LOCATION:British Antarctic Survey\, Room 307
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