Time-lapse Acoustic Imaging of Oceanic Fronts and Eddies
Seismic reflection surveying is used to generate acoustic images of the water column. This technique employs conventional multi-channel equipment which is used to image the solid Earth. In the water column, acoustic impedance contrasts are produced by variations in temperature and, to some extent, s...
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ftunivcam:oai:www.repository.cam.ac.uk:1810/284560 2023-07-30T03:56:43+02:00 Time-lapse Acoustic Imaging of Oceanic Fronts and Eddies Gunn, Kathryn Louise 2018-11-02T13:58:49Z application/pdf https://doi.org/10.17863/CAM.31936 https://www.repository.cam.ac.uk/handle/1810/284560 en eng Department of Earth Sciences University of Cambridge doi:10.17863/CAM.31936 https://www.repository.cam.ac.uk/handle/1810/284560 All rights reserved https://www.rioxx.net/licenses/all-rights-reserved/ Seismic Oceanography Oceanic Fronts and Eddies Inversion Thesis Doctoral Doctor of Philosophy (PhD) PhD in Seismic Oceanography 2018 ftunivcam https://doi.org/10.17863/CAM.31936 2023-07-10T21:32:07Z Seismic reflection surveying is used to generate acoustic images of the water column. This technique employs conventional multi-channel equipment which is used to image the solid Earth. In the water column, acoustic impedance contrasts are produced by variations in temperature and, to some extent, salinity. Acoustic impulses generated by an array of airguns suspended behind a vessel are reflected from these contrasts and recorded on long cables of hydrophones that are towed below the sea-surface. In this way, two- and three-dimensional images of thermohaline circulation can be generated. Critically, these images have equal vertical and horizontal resolutions of \textit{O}(10)~m. Here, I describe, process, and analyse a calibrated two-dimensional seismic survey from the Bellingshausen Sea of the Southern Ocean and a three-dimensional seismic survey from the Brazil-Falkland Confluence located offshore Uruguay. First, the Bellingshausen survey was designed to image the thermohaline structure across the west Antarctic shelf where warm-core eddies are reported. Processed and calibrated seismic images reveal the detailed thermohaline structure of Circumpolar Deep Water. Many warm-core eddies are observed, which have diameters of 1--12~km and thicknesses of 100--200~m. Pre-stack analysis demonstrates that this eddy field is being advected onto the shelf at speeds of \textit{O}(0.1)~m~s$^{-1}$. An iterative inverse modelling procedure is used to convert reflectivity into temperature and salinity, which confirms that the eddies have anomalously warm centres (i.e. $\sim$1$^{\circ}$C). These results have significant implications for ice shelf melting. Secondly, the Uruguay survey is used to investigate a large-scale frontal system. Although this system has been studied using hydrographic methods, these studies either have limited spatial resolution or have restricted depth penetration. The three-dimensional seismic survey, which was acquired in a `racetrack' pattern, permits the volume to be interrogated. Since the frontal ... Doctoral or Postdoctoral Thesis Antarc* Antarctic Bellingshausen Sea Ice Shelf Southern Ocean Apollo - University of Cambridge Repository Antarctic Bellingshausen Sea Southern Ocean Uruguay |
institution |
Open Polar |
collection |
Apollo - University of Cambridge Repository |
op_collection_id |
ftunivcam |
language |
English |
topic |
Seismic Oceanography Oceanic Fronts and Eddies Inversion |
spellingShingle |
Seismic Oceanography Oceanic Fronts and Eddies Inversion Gunn, Kathryn Louise Time-lapse Acoustic Imaging of Oceanic Fronts and Eddies |
topic_facet |
Seismic Oceanography Oceanic Fronts and Eddies Inversion |
description |
Seismic reflection surveying is used to generate acoustic images of the water column. This technique employs conventional multi-channel equipment which is used to image the solid Earth. In the water column, acoustic impedance contrasts are produced by variations in temperature and, to some extent, salinity. Acoustic impulses generated by an array of airguns suspended behind a vessel are reflected from these contrasts and recorded on long cables of hydrophones that are towed below the sea-surface. In this way, two- and three-dimensional images of thermohaline circulation can be generated. Critically, these images have equal vertical and horizontal resolutions of \textit{O}(10)~m. Here, I describe, process, and analyse a calibrated two-dimensional seismic survey from the Bellingshausen Sea of the Southern Ocean and a three-dimensional seismic survey from the Brazil-Falkland Confluence located offshore Uruguay. First, the Bellingshausen survey was designed to image the thermohaline structure across the west Antarctic shelf where warm-core eddies are reported. Processed and calibrated seismic images reveal the detailed thermohaline structure of Circumpolar Deep Water. Many warm-core eddies are observed, which have diameters of 1--12~km and thicknesses of 100--200~m. Pre-stack analysis demonstrates that this eddy field is being advected onto the shelf at speeds of \textit{O}(0.1)~m~s$^{-1}$. An iterative inverse modelling procedure is used to convert reflectivity into temperature and salinity, which confirms that the eddies have anomalously warm centres (i.e. $\sim$1$^{\circ}$C). These results have significant implications for ice shelf melting. Secondly, the Uruguay survey is used to investigate a large-scale frontal system. Although this system has been studied using hydrographic methods, these studies either have limited spatial resolution or have restricted depth penetration. The three-dimensional seismic survey, which was acquired in a `racetrack' pattern, permits the volume to be interrogated. Since the frontal ... |
format |
Doctoral or Postdoctoral Thesis |
author |
Gunn, Kathryn Louise |
author_facet |
Gunn, Kathryn Louise |
author_sort |
Gunn, Kathryn Louise |
title |
Time-lapse Acoustic Imaging of Oceanic Fronts and Eddies |
title_short |
Time-lapse Acoustic Imaging of Oceanic Fronts and Eddies |
title_full |
Time-lapse Acoustic Imaging of Oceanic Fronts and Eddies |
title_fullStr |
Time-lapse Acoustic Imaging of Oceanic Fronts and Eddies |
title_full_unstemmed |
Time-lapse Acoustic Imaging of Oceanic Fronts and Eddies |
title_sort |
time-lapse acoustic imaging of oceanic fronts and eddies |
publisher |
Department of Earth Sciences |
publishDate |
2018 |
url |
https://doi.org/10.17863/CAM.31936 https://www.repository.cam.ac.uk/handle/1810/284560 |
geographic |
Antarctic Bellingshausen Sea Southern Ocean Uruguay |
geographic_facet |
Antarctic Bellingshausen Sea Southern Ocean Uruguay |
genre |
Antarc* Antarctic Bellingshausen Sea Ice Shelf Southern Ocean |
genre_facet |
Antarc* Antarctic Bellingshausen Sea Ice Shelf Southern Ocean |
op_relation |
doi:10.17863/CAM.31936 https://www.repository.cam.ac.uk/handle/1810/284560 |
op_rights |
All rights reserved https://www.rioxx.net/licenses/all-rights-reserved/ |
op_doi |
https://doi.org/10.17863/CAM.31936 |
_version_ |
1772814246461046784 |