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Properties of a marine ice layer under the Amery Ice Shelf, East Antarctica

Citation

Craven, M and Allison, I and Fricker, HA and Warner, R, Properties of a marine ice layer under the Amery Ice Shelf, East Antarctica, Journal of Glaciology, 55, (192) pp. 717-728. ISSN 0022-1430 (2009) [Refereed Article]


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Copyright Statement

Copyright 2009 International Glaciological Society

DOI: doi:10.3189/002214309789470941

Abstract

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.

Item Details

Item Type:Refereed Article
Keywords:Amery ice shelf, marine ice, basal freezing, basal melt
Research Division:Earth Sciences
Research Group:Physical Geography and Environmental Geoscience
Research Field:Glaciology
Objective Division:Environment
Objective Group:Climate and Climate Change
Objective Field:Climate and Climate Change not elsewhere classified
Author:Craven, M (Mr Mike Craven)
Author:Allison, I (Dr Ian Allison)
Author:Warner, R (Dr Roland Warner)
ID Code:100643
Year Published:2009
Web of Science® Times Cited:50
Deposited By:CRC-Antarctic Climate & Ecosystems
Deposited On:2015-05-22
Last Modified:2015-09-08
Downloads:220 View Download Statistics

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