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Modelling iceberg tracks around Antarctica

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Matthews, David Evan (2010) Modelling iceberg tracks around Antarctica. Research Master thesis, University of Tasmania.

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Abstract

The drift tracks of five large tabular icebergs drifting around Antarctica were
simulated using a dynamic model similar to that used by Lichey and Hellmer (2001)
with the exception that sea ice strength was not considered as a condition of iceberg
trapping. Three of these iceberg tracks (737n165, 74n131 and BlOB) drifted in the
Ross Sea for periods of time between 1995 and 2000. Iceberg BO9A drifted along the
coast of East Antarctica along the Antarctic coastal current and entered the Weddell
Sea. Iceberg BlOA drifted along the West Antarctic region initially moving west in
the Antarctic coastal current then moved north near 130°W before entering the
Antarctic Circumpolar current and moving east through Drake Passage. The input
fields of wind, ocean and sea ice velocity, and sea ice concentration are used in the
model to simulate the drift of these icebergs. The iceberg sizes range from 200 km2
to 2070 lcm2, with drift tracks lasting between 1 and 8 years.
Only periods that indicated movement of the iceberg from one composite image to
the next were simulated, providing a more focussed model track. Various model
simulations are conducted using ocean velocity fields at either 103 m or 238 m
depths and three variations of the iceberg trapping criteria dependent on sea ice
concentration. Two of these variations are based on the sea ice concentration at the
iceberg position (using 85% or 90% sea ice concentration as the trapping criteria)
and the other excludes iceberg trapping altogether. The assumption of a trapped
iceberg instantly moving at the velocity of the sea ice, regardless of previous iceberg
velocity, returns poor results and at times moves the iceberg in the opposite direction.
If the iceberg is released from the sea ice, all the forces in the model become active
and large amplitude inertial oscillations are initiated in the drift track.
An analysis of the force contribution to the iceberg velocity is conducted and it was
found that the Coriolis and sea surface slope are close to opposing forces, keeping
the iceberg within the ocean current and the air drag can influence the iceberg drift
when sufficiently strong enough. An RMS analysis between the final position of the
model iceberg and the position of the observed drift track for the same date are
assessed for each model track. The model simulation ocean currents near the base of
the iceberg (238 m) and no iceberg trapping attain the least rms error in position
between the model and the observed iceberg track for all but two icebergs, B1OA and
BO9A. For these icebergs, the model simulations providing the least error were 85%
iceberg trapping criteria and 238 m ocean currents for both icebergs.
This result shows that the sea ice movement is well represented in East and West
Antarctica, and not so well in the Ross Sea, as model simulations performed better
with no iceberg trapping. These results show that trapping an iceberg and instantly
moving that iceberg with the sea ice floe doesn't fully necessarily capture the drift of
large tabular icebergs. The iceberg model is strongly dependent on the data
representing the ocean currents and sea ice movement to sufficiently model the drift
of large tabular icebergs.

Item Type: Thesis (Research Master)
Keywords: Icebergs, Icebergs
Copyright Holders: The Author
Copyright Information:

Copyright 2010 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (MSc)--University of Tasmania, 2010. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:55
Last Modified: 15 Sep 2017 06:57
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