The Variation in the Ice Sheet of Mizuho Plateau, East Antarctica (Abstract)

The Japanese Antarctic Research Expedition (JARE) has conducted glaciological studies on Mizuho Plateau since 1981. We have already reported that the ice sheet flowing from Mizuho Plateau into Shirase Glacier is thinning at a rate of about 70 cm/year and that the profile of the distribution of basal shear stress is similar to that of surging glaciers.A 5 year glaciological programme on Mizuho Plateau and in east Queen Maud Land is now being carried out and we have obtained the following new results:(1) The ice sheet in the down-stream region (where ice elevation is lower than about 2400 m) is thinning, based on measurements of horizontal and vertical flow velocity, strain-rate, the slope of the ice surface, the accumulation rate and densification of snow.(2) δ18O analysis of deep ice cores obtained at Mizuho Station (2240 m a.s.l.) and point G2 (1730 m a.s.l.) shows that δ18O increased about 200 years ago at Mizuho Station and about 400 years ago at point G2. If we can assume that the increase in δ18O is caused by the thinning of the ice sheet, then this result means that this thinning propagates to up-stream areas.(3) Radio-echo-sounding measurements on Mizuho Plateau show that the ice base in the down-stream region is wet. This supports the result described in (1), since the basal sliding due to a wet base causes ice-sheet thinning, as proposed in our previous studies.In summary, a possible explanation of ice-sheet variation on Mizuho Plateau is as follows: the thinning of the ice sheet, caused by the basal sliding due to basal ice melting, started at Shirase Glacier and has been propagating up-stream to reach its present position. A simple calculation, using flow velocities, shows that the thinning started at Shirase Glacier about 1500–2000 years ago.