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On the Antarctic contribution to Holocene sea-level

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Goodwin, ID (1995) On the Antarctic contribution to Holocene sea-level. PhD thesis, University of Tasmania.

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Abstract

Holocene glacial fluctuations of Antarctica are investigated using a combined glacial
geological and glaciological approach. An understanding of the timing, forcing and
sea-level contribution of these glacial fluctuations is crucial to the interpretation of
global eustatic sea-level changes during the Holocene and the present. As a baseline
for the Holocene studies, the recent surface mass balance rate distribution of Antarctica
and its controlling factors are determined with respect to case studies in the Wilkes
Land and the Lambert Glacier drainage basins. The variation in surface mass balance
rates and mean annual oxygen isotope values over the last 50 years are interpreted
from stratigraphic analyses of several shallow firn cores from these drainage basins.
The surface mass balance rate is calculated to vary with surface air temperature by
20%/°C in the ice sheet interior, and by 25%/°C in the coastal margins. This variation
is in response to changes in atmospheric circulation, surface air temperature and sea
ice extent.
The Holocene climate pattern is analysed with respect to the oxygen isotope records
from the deep ice cores and the oceanic sediment cores, and is defined into periods
where temperature has deviated up to 1-2°C from the long-term Holocene mean. The
corresponding terrestrial and marine glacial geological evidence for Holocene glacial
fluctuations in the south-western Pacific Ocean, the Indian Ocean, and the Ross Sea
sectors of East Antarctica is re-examined together with a case study of the Holocene
glacial history of the Windmill Islands and the Law Dome ice sheet, in East Antarctica.
An interpretation of the ice expansion during the Last Glacial Maximum and the
subsequent melting history of the Law Dome ice sheet during the Early-Mid Holocene,
is made from field observations of raised shorelines and the chronostratigraphy of lake
sediments and abandoned Adelie penguin rookeries on the Windmill Islands. The
Mid-Late Holocene evolution of the Law Dome ice sheet margin is determined from
the stratigraphy, structure, morphology, isotopic, solute and sediment composition of
basal ice exposures and the Loken Moraines. The results from the Law Dome case
study support the view that contraction of the outlet glaciers was established before
8,000 years B.P. with the outer Windmill Islands, adjacent to the Vanderford Glacier,
ice free at this time. Contraction of the grounded ice margins lagged the outlet glaciers
with the inner Windmill Islands deglaciated by 5,500 years B.P.. Subsequently, the
ice margin continued to retreat to a position further inland than the present until 4,500
years B.P.. During this period the East Antarctic outlet glaciers were at their
maximum Holocene expansion. Between 4,000 to 1,000 years B.P. it is concluded
that the Law Dome and the East Antarctic grounded ice margins expanded with a
partial contraction between 500 years B.P. to the present.
Relative sea-level changes and variation in surface mass balance rates throughout the
Holocene are tested by a sensitivity analysis of the Lambert Glacier/Amery Ice Shelf
system, the Law Dome and Wilkes Land to determine the forcing mechanisms for the
glacial fluctuations. The palaeo-surface mass balance rates are calculated for the Early
Holocene Climatic Optimum, the Mid Holocene cool period, and the Late Holocene
warm and cool phases, using the interpreted 20-25%/°C variation in surface mass
balance with air temperature. The sensitivity analyses confirm that the size of
Antarctica is controlled by its dual response to sea-level and climate changes, with
expansion initiated by relative sea-level lowering and nourished by a positive surface
mass balance. The relative sensitivities are characterised by the outlet glaciers leading
the grounded ice sheet margins and the alpine glaciers, both in the Early Holocene
contraction and in the Mid-Late Holocene expansion. It is hypothesised that variation
in palaeo-surface mass balance rates during the Holocene has partially offset the sea-level
rise contribution of the post-glacial contraction of Antarctica. An equivalent sea-level
curve for Antarctica is constructed from the differential surface mass balance
contributions and from the post-glacial melting history. The validity of the hypothesis
is tested by comparing the derived sea-level curve to the relative sea-level records on
mid-oceanic islands. The maximum contribution from Antarctica to post-glacial sealevels
occurred at 4,000 years B.P. when there was widespread retreat of the East
Antarctic outlet glaciers, and the grounded ice sheet margins. This is synchronous
with the geomorphological evidence for high sea-level stands on the mid-oceanic
islands. Antarctica contributed a slight lowering to sea-level between 4,000 to 1,000
years B.P.. During this century the probable Antarctic sea-level contribution was
calculated to have varied from a sea-level contribution of +0.25 mm a -1 prior to 1970
followed by a contribution of -0.15 mm a-1 since 1970. It is suggested that these
contributions to Holocene sea-levels provide a better fit to the oceanic sea-level records
than those produced by models based on the continuing exponential melting and retreat
of the Antarctic Ice Sheet throughout the Holocene.

Item Type: Thesis (PhD)
Keywords: Sea level, Paleoclimatology
Copyright Holders: The Author
Copyright Information:

Copyright 1995 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, 1995. Includes bibliographical references (p. 294-315)

Date Deposited: 08 Dec 2014 23:56
Last Modified: 11 Mar 2016 05:55
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