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2009
Craven, M, Allison I, Fricker HA, Warner R.  2009.  Properties of a marine ice layer under the Amery Ice Shelf, East Antarctica. Journal of Glaciology. 55:717-728. AbstractWebsite

The Amery Ice Shelf, East Antarctica, undergoes high basal melt rates near the southern limit of its grounding line where 80% of the ice melts within 240 km of becoming afloat. A considerable portion of this later refreezes downstream as marine ice. This produces a marine ice layer up to 200 m thick in the northwest sector of the ice shelf concentrated in a pair of longitudinal bands that extend some 200 km all the way to the calving front. We drilled through the eastern marine ice band at two locations 70 km apart on the same flowline. We determine an average accretion rate of marine ice of 1.1 +/- 0.2 m a(-1), at a reference density of 920 kg m(-3) between borehole sites, and infer a similar average rate of 1.3 +/- 0.2 m a(-1) upstream. The deeper marine ice was permeable enough that a hydraulic connection was made whilst the drill was still 70-100 m above the ice-shelf base. Below this marine close-off depth, borehole video imagery showed permeable ice with water-filled cavities and individual ice platelets fused together, while the upper marine ice was impermeable with small brine-cell inclusions. We infer that the uppermost portion of the permeable ice becomes impermeable with the passage of time and as more marine ice is accreted on the base of the shelf. We estimate an average closure rate of 0.3 m a(-1) between the borehole sites; upstream the average closure rate is faster at 0.9 m a(-1). We estimate an average porosity of the total marine ice layer of 14-20%, such that the deeper ice must have even higher values. High permeability implies that sea water can move relatively freely through the material, and we propose that where such marine ice exists this renders deep parts of the ice shelf particularly vulnerable to changes in ocean properties.

2002
Fricker, HA, Young NW, Allison I, Coleman R.  2002.  Iceberg calving from the Amery Ice Shelf, East Antarctica. Annals of Glaciology, Vol 34, 2002. 34( Winther JG, Solberg R, Eds.).:241-246., Cambridge: Int Glaciological Soc   10.3189/172756402781817581   Abstract

We investigate the iceberg-calving cycle of the Amery Ice Shelf (AIS), East Antarctica, using evidence acquired between 1936 and 2000. The most recent major iceberg-calving event occurred between late 1963 and early 1964, when a large berg totalling about 10 000 km(2) in area broke From the ice front. The rate of forward advance of the ice front is presently 1300-1400 m a(-1). At this rate of advance, based on the present icefront position front recent RADARSAT imagery, it would take 20-25 years to attain the 1963 (pre-calve) position, suggesting that the AIS calving cycle has a period of approximately 60-70 years. Two longitudinal (parallel-to-flow) rifts, approximately 25 km apart at the AIS front, are observed in satellite imagery acquired over the last 14+ years. These rifts have formed at suture zones the shelf where neighbouring now-bands have separated in association with transverse spreading. The rifts were 15 km (rift A) and 26 km (rift B) in length in September 2000, and will probably become the sides of a large tabular iceberg (23 km x 25 km). A transverse (perpendicular-to-flow) fracture, visible at the upstream end of rift A in 1996, had propagated 6 km towards rift B by September 2000; when it meets rift B the iceberg will calve. A satellite image acquired in 1962 shows an embayment of this size in the AIS front, hence we deduce that this calving pattern also occurred during the last calving cycle, and therefore that the calving behaviour of the AIS apparently follows a regular pattern.