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Estimating Geostrophic Shear from Seismic Images of Oceanic Structure

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  • 1 Bullard Laboratories, University of Cambridge, Cambridge, United Kingdom
  • | 2 BP Institute, and Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom
  • | 3 Department of Earth Sciences, University of Durham, Durham, United Kingdom
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Abstract

It is shown that geostrophic vertical shear estimates can be recovered from seismic (i.e., acoustic) images of thermohaline structure. In the Southern Ocean, the Antarctic Circumpolar Current forms a loop within the Falkland Trough before it flows northward into the Argentine Basin. Seismic profiles that cross this loop show the detailed structure of different water masses with a horizontal resolution of O(10 m). Coherent seismic reflections are tilted in response to current flow around the Falkland Trough. Average slopes were measured on length scales that are large enough to ensure that the geostrophic approximation is valid (i.e., with a Rossby number <0.1). By combining shear estimates with satellite altimetric measurements and acoustic Doppler current profiles, geostrophic velocities can be calculated throughout the data volume. This technique for estimating geostrophic vertical shear from legacy seismic images yields useful information about the spatial and temporal variation of mesoscale circulation.

Department of Earth Sciences, University of Cambridge Contribution Number ESC.2157.

Corresponding author address: Katy Sheen, National Oceanography Centre, Southampton, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, United Kingdom. E-mail: k.sheen@soton.ac.uk

Abstract

It is shown that geostrophic vertical shear estimates can be recovered from seismic (i.e., acoustic) images of thermohaline structure. In the Southern Ocean, the Antarctic Circumpolar Current forms a loop within the Falkland Trough before it flows northward into the Argentine Basin. Seismic profiles that cross this loop show the detailed structure of different water masses with a horizontal resolution of O(10 m). Coherent seismic reflections are tilted in response to current flow around the Falkland Trough. Average slopes were measured on length scales that are large enough to ensure that the geostrophic approximation is valid (i.e., with a Rossby number <0.1). By combining shear estimates with satellite altimetric measurements and acoustic Doppler current profiles, geostrophic velocities can be calculated throughout the data volume. This technique for estimating geostrophic vertical shear from legacy seismic images yields useful information about the spatial and temporal variation of mesoscale circulation.

Department of Earth Sciences, University of Cambridge Contribution Number ESC.2157.

Corresponding author address: Katy Sheen, National Oceanography Centre, Southampton, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, United Kingdom. E-mail: k.sheen@soton.ac.uk
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