Ice shelf history determined from deformation styles in surface debris

AbstractThis paper presents InSAR-derived ice shelf velocities and observations of surface debris deformation on the McMurdo Ice Shelf (MIS). Ice shelf velocities show that the MIS has a low surface velocity, with debris-laden parts of the ice shelf in the area known as the ‘swirls’ averaging speeds of c. 3 m a-1 increasing to c. 16 m a-1 at the ice front. Analysis of the fold patterns within moraine ridges on the ice surface reveals a deformational history inconsistent with the present velocity measurements. Polyphase, isoclinal folding within moraine ridges at the surface are interpreted to have formed through intense deformation by past ice flow in a NNW orientation. The velocities and styles of deformation indicate that the majority of debris on the ice shelf was originally transported into the area by a large and dynamic ice sheet/ice shelf system entirely different to that of the present configuration. Although the age of this event is unknown, it is possible that this debris has been exposed on the surface of the ice shelf since the last glacial maximum.</jats:p

Supraglacial lakes on the Larsen B ice shelf, Antarctica, and at Paakitsoq, West Greenland:A Comparative Study

This is the accepted manuscript. The final version is available from Ingenta Connect at http://www.ingentaconnect.com/content/igsoc/agl/2014/00000055/00000066/art00001.Supraglacial meltwater lakes trigger ice-shelf break-up and modulate seasonal ice\ud sheet flow, and are thus agents by which warming is transmitted to the Antarctic\ud and Greenland ice sheets. To characterize supraglacial lake variability we perform a\ud comparative analysis of lake geometry and depth in two distinct regions, one on the\ud pre-collapse (2002) Larsen B Ice Shelf, and the other in the ablation zone of\ud Paakitsoq, a land-terminating region of the Greenland Ice Sheet. Compared to\ud Paakitsoq, lakes on the Larsen B Ice Shelf cover a greater proportion of surface area\ud (5.3% vs. 1%), but are shallower and more uniform in area. Other aspects of lake\ud geometry, such as eccentricity, degree of convexity (solidity) and orientation, are\ud relatively similar between the two regions. We attribute the notable difference in\ud lake density and depth between ice-shelf and grounded ice to the fact that ice shelves\ud have flatter surfaces and less distinct drainage basins. Ice shelves also possess more\ud stimuli to small-scale, localized surface elevation variability due to the various\ud structural features that yield small variations in thickness and which float at\ud different levels by Archimedes? principle.We acknowledge the support of the U.S. National Science Foundation under grant ANT-0944248