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Abstract

In order to gain a proper understanding of the present state of the Earth's
cryosphere in relation to its environment, it is desirable to have a sound knowledge
of the glacial history which led to the present conditions. In this study, the ice
sheets of the northern hemisphere and the Antarctic are modelled through the
last glacial cycle in order to gain some understanding of both present and palaeo
environments. The results of the energy balance model of Budd and Rayner
(1993), which was driven by orbital variations in radiation as well as internal
climate and ice sheet feedbacks, provides the shape of the time series of primary
climate forcing for global ice sheet modelling. The amplitude of the climate
forcing comes from matching palaeo-reconstructions of ice margins, sea level,
temperature and accumulation rate. The ice sheet model is coupled to an ice
shelf model and includes isostatic adjustment of the bedrock as well as simple
thermodynamics.
Results for the northern hemisphere modelling indicated that forcing with a
maximum temperature change of about -13°C at the southern margin of the ice
sheets leads to ice sheet extents in general agreement with palaeo-observations.
This temperature change is representative of the ablation region over the ice margin
where there is a sharp contrast between temperature changes over land and
the much larger changes over the interior of the ice sheet. Ice sheet extent is also
found to be dependent on the initial bed topography, but is found to be weakly
dependent on changes to the sea level and the base accumulation distribution
outside the ice sheet 'elevation-desert' effect. The existence and extent of a large
ice shelf in the Arctic Ocean however, is found to be strongly dependent on the
net accumulation rate. An estimate of eustatic sea level change through the last
glacial cycle based on the modelling of the northern hemisphere ice sheets also
agrees reasonably well with other sea level change reconstructions. The timing
and extent of the 'fresh water pulse' from the maximum rate of deglaciation
exhibits some correspondence with the initiation of the Younger Dryas cooling
episode.
The Antarctic is shown to be sensitive to changes in sea level and accumulation
rate, and it is found that these influences have largely opposing effects. While
the sea level change strongly influences ice thickness in regions of significant
basal sliding, variation in the accumulation rate offsets this effect and there is
little modelled grounding line movement during the glacial cycle. This leads to
only a small net contribution to post glacial maximum sea level change from the
Antarctic, in the order of 1m. The West Antarctic region is very sensitive to
the sliding parameterisation and grounding line dynamics and consequently the
results are not as robust as those for East Antarctica. The derived present state
of the ice sheet shows that in central East Antarctica, there is ~20% positive
mass balance still remaining, whereas nearer the coast the ice sheet is closer to
balance. It is concluded that prior to the onset of recent anthropogenic influences,
the net Antarctic mass balance was near to zero with only a very small positive
net balance contributing slightly towards sea level lowering.

Item Type:	Thesis - PhD
Authors/Creators:	Coutts, Brendan (Brendan Campion)
Keywords:	Ice sheets, Glaciology
Copyright Holders:	The Author
Copyright Information:	Copyright 1999 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:	Thesis (Ph.D.)--University of Tasmania, 1999. Includes bibliographical references
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