Research
Antarctica phase III (1993-1997)
Dynamics of the Antarctic ice cap and climatic changes
Promotor
Professor Hugo Decleir
Vrije Universiteit Brussel
Geografisch Instituut
Pleinlaan, 2
B-1050 BRUSSELS
Phone: +32 (0)2 629 33 83
Fax: +32 (0)2 629 33 78
E-mail: hdecleir@vub.ac.be
Topics
In this study we examined:
- the stability of the ice sheet in East Dronning Maud Land and Enderby Land where it is drained by a large fast-flowing continental ice stream (Shirase Glacier); and,
- the regional behaviour of the Antarctic ice sheet in East Dronning Maud Land in function of environmental change over a period of the last 200,000 years. Both tasks were accomplished by numerical modelling of the ice sheet system and by satellite remote sensing.
For this purpose we developed a flexible and multi-purpose flow line model allowing us to study the relevant glaciological processes in ice stream behaviour on the one hand and capable of linking, on sound physical principles, the observed climatic signal from ice core data with the geomorphological data as observed in the ice free areas, on the other hand. With respect to the observed glaciological parameters we also developed a method for deriving glacier variations from sequential satellite images by an automatic matching technique.
The analysis itself focused on the period of the last 200,000 years with special interest in the last glacial-Holocene transition and the present day dynamical situation:
- Since field evidence from Shirase Drainage Basin reports
a rapid thinning of the ice sheet, model experiments were
carried out to shed a light on the relevant physical processes
responsible for ice stream behaviour. Indeed, from preliminary
experiments (Pattyn and Decleir, 1995) it
was found that the large thinning rate in Shirase Drainage
Basin could not be explained as a response to the climate
signal alone. Some other mechanism should account for this.
By carrying out simulations with different basal boundary conditions, a thermally regulated cyclic behaviour, related to the hydraulic conditions at the bed(water pressure, basal melting and meltwater flow) could be observed, giving rise to a partial disintegration of the ice sheet (Pattyn, 1996). Yet, the ice loss was confined to the stream area and did not influence the inland ice sheet near the Polar Plateau. The high imbalance values(in accord with observations) could be explained by the small period in the cyclicity, hence a large ice discharge was not necessary. Whether this mechanism applies to Shirase Glacier awaits future field work to disentangle the basal properties of this fast-flowing outlet glacier. - Recent glacio-geological and geomorphological field evidences
in the neighbouring Sør Rondane Mountains point -
as elsewhere in Antarctica - to a relative stable ice sheet
cover during the last million years. This was confirmed by
applying different model scenarios of the behaviour of Gjelbreen,
an outlet glacier of this mountain range. Results of the
'best fit' scenario, i.e. the model outcome which is closest
to the field evidence, showed that the present ice sheet
in the Sør Rondane is close to its maximum position
of the last glacial-interglacial period. This proves that
the ice sheet is out of phase with the climatic signal and
explains the small observed differences in glacier stand
between the present and the maximum.
However, over the last 200,000 years the glacier variations amount to 100-200 m. Our modelling experiments clearly indicate that both the position on the glacier (coastal, mountain and inland ice sheet) and the timing of the response is essential to make a comparison with field observations elsewhere.
References:
Pattyn F. (1996): Numerical modelling of a fast flowing outlet glacier: experiments with different basal conditions. Ann. Glaciol., 23: 237-246.
Pattyn F. and Decleir H. (1995): Numerical simulation of Shirase Glacier, East Queen Maud Land, Antarctica. Proc. NIPR Symp. Polar Meteorol. Glaciol., 9: 87-109.
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