| Summary: | In this paper, the global characteristics of a polar ice sheet are investigated. When looking at a drainage system as a whole, conservation of heat yields a very simple functional relation. Coupling this relation to an equation describing the large-scale dynamics of a drainage system makes it possible to study the feedback of thermodynamics on the ice-mass discharge. It is found that the temperature-ice flow feedback (including the effect of basal meltwater) can give rise to bifurcation. For certain combinations of air temperature and mass balance, two stable flow regimes are possible for a polar ice sheet: fast flow, with high basal temperatures and slow flow, with low basal temperatures. Basal melting is strongly reduced when the accumulation rate increases. Thus a polar drainage system can be brought into the fast flow regime (with meltwater present) by reducing the mass balance, or by increasing the air temperature. The calculation of the global heat budget is also applied to flow lines of the antarctic ice sheet. For the flow line into the Ross Sea we find that at present a large imbalance exists. It seems that the ice sheet is cooling here, and consequently, building up.
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