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Dynamics of the Antarctic ice cap and climate changes

Antarctica phase IV (1997-2000)

Dynamics of the Antarctic ice cap and climate changes
(a contribution to EPICA)

Promotor

Professor Hugo Decleir and Frank Pattyn
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

The project ‘Dynamics of the Antarctic ice cap and climate changes’ is a Belgian contribution to the European Project for Ice coring in Antarctica. This project examined 1) 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 2) 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 a flexible and multi-purpose flow line model was developed allowing 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 a method was developed 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.

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