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Seismic surveys of the Amery Ice Shelf, East Antarctica: an investigation of meteoric and marine ice, the ocean cavity and the anisotropic crystalline structure of strained ice

thesis
posted on 28.03.2022, 21:32 authored by Kathleen Louise McMahon
A multipurpose seismic study of the Amery Ice Shelf (AIS), East Antarctica, was undertaken between 2002/03 and 2005/06 with the aim of expanding glaciological knowledge of the structure of the AIS. Seismic reflection surveys were carried out at localities G2A, AM01, AM04, and CT. CT is situated across the Lambert Glacier (LG)-Mawson Escarpment Ice Stream (MEIS) flow boundary. The results show ~722 m total ice at G2A, and a sharp 15 m decrease from 672 m to 657 m at the LG-MEIS ice boundary at CT. Strong reflections just under the ice base correspond to cooler water temperatures, mapping an 18-36 m layer of basal melt. A pycnocline is present in most seismic records, showing the boundary between Ice Shelf Water (ISW) and High Salinity Shelf Water. ISW thicknesses are 137-140 m at G2A and CT, and 75-95 m at AM01. At sites of marine ice accretion (AM01 and AM04) seismic data reveals the meteoric-marine ice boundary at 277 m and 394-401 m respectively. This matches depths measured by the Amery Ice Shelf Ocean Research (AMISOR) hot-water drilling project. Interestingly, the ice shelf base depth as measured by AMISOR produced no reflection in the seismic data at AM01 and AM04. A reflection from the hydraulic connection depth instead appears at 376 m at AM01 and 533-544 m at AM04. Seafloor depth below the surface is ~1317-1357 m around G2A, 975-992 m around AM04, 814-824 m at AM01 and 1120 m at the CT Line, although here the seismic data also shows a hill with its crest at 1083 m depth. Perpendicular refraction surveys across major flow unit boundaries revealed negligible to weak azimuthal differences in P wave ice velocities, with no significant variation found within the upper ~100 m of ice shelf ice. The results showed a general range of 0.1-2.2% variation, with only one site displaying a 4.3% variation which may or may not indicate an anisotropic ice fabric.

History

Table of Contents

1. Thesis introduction and aims -- 2. The Amery Ice Shelf: a brief guide to everything -- 3. Methodology -- 4. G2A: a three year case study -- 5. AM01, AM03 and AM04: seismics vs AMISOR CTD data -- 6. Pycnoclines in the water column beneath the AIS -- 7. Azimuthal anisotropy in strained ice of the AIS -- Appendix C.

Notes

"A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) by Research in Geophysics". Bibliography: p. [194]-203 "February 2012".

Awarding Institution

Macquarie University

Degree Type

Thesis PhD

Degree

Thesis (PhD), Macquarie University, Faculty of Science, Dept. of Earth and Planetary Sciences

Department, Centre or School

Department of Earth and Planetary Sciences

Year of Award

2012

Principal Supervisor

Mark Lackie

Rights

Copyright disclaimer: http://www.copyright.mq.edu.au/ Copyright Kathleen McMahon 2012

Language

English

Jurisdiction

Antarctic Ocean; Antarctica

Extent

1 online resource (xv, 231 p.) ill. (some col.), maps

Former Identifiers

mq:20376 http://hdl.handle.net/1959.14/177398 1673902