Physiography, flow characteristics and vulnerability of the Southern McMurdo Ice shelf, Antarctica

Clifford, Andrew E. (Andrew Eliot)

global environmental change. Such changes are of particular concern in West Antarctica the world's largest marine ice sheet (the West Antarctic Ice Sheet, WAIS) could cause m global sea level rise, should it collapse. Many studies have, therefore, focused on the largest ice shelves buffering the WAIS from the oceans (the Ross and Ronne-Filchner ice ves). However, an understanding of the dynamics and stability of these large ice shelves is 'ted by their inaccessibility and the complex behaviour of the ice streams and glaciers that them. Conversely, the McMurdo Ice Shelf (MIS) at the north-west edge of the Ross Ice (RIS) has dimensions of only 100 x 50 km and is relatively accessible, making it a good 'ILIV''"'H'"~~ analogue for the glacial processes of the RIS. uH,...,~,J~v5,·,.., data for the northern MIS are abundant and show that this part of the ice shelf is fed by the RIS, the Ross Island glaciers and the Koettlitz Glacier. In contrast, the present glaciologic regime of the southern MIS (SMIS; between the volcanic landmasses of Black Island, Mount Discovery and Minna Bluff) has mainly been inferred from limited spot measurements published over 30 years ago (Swithinbank, 1970). The SMIS is distinctive in that glacial deposits are preserved at its margins and on its surface, providing evidence for former ice shelf and ice sheet activity in southern McMurdo Sound. Consequently, there is potential to evaluate how an ice shelf responds to environmental change, as, on the SMIS, the preserved glacial deposits can be interpreted in terms of active processes that can be readily measured within the confines of a comparatively small area. The major motivation for the present research has been to determine the present glaciologic regime of the SMIS by compiling data-sets relating to its physiography and flow characteristics, with which former inferences can be tested and vulnerability of the ice shelf to climate change can be assessed. Geophysical data (GPS, ground-penetrating radar, seismic, aeromagnetic and gravity surveys) were acquired on the SMIS over three consecutive austral summers (2002/03-2004/05) in conjunction with ANDRILL site investigations. These data have been compiled with morphometric analyses (satellite images, aerial photographs and field observations) to identify: (i) surface accumulation/ablation areas, (ii) ice surface elevation, (iii) ice shelf thickness, (iv) horizontal flow velocities, (v) pinning points/grounding zones (vi) areas of marine ice accretion and, (vii) active sediment transport processes. iii The results show that south-westerly katabatic winds deposit snow and sediment in the surface accumulation area south of Black and White islands, where surface elevation is highest (>-20 m ellipsoid height) and the ice shelf is thickest (190 ± 10 m). Surface elevation and ice thickness decrease towards the south (Minna Bluff) and west (Moraine Strait), where the katabatic winds are strongest, and cause surface ablation. The flow pattern follows the same directional trend, indicating that it is driven by gravitational creep. Flow is regulated by frictional resistance at grounding zones, located at the landmass margins and below a midshelf ice rise, where a seamount intersects the base of the SMIS. The horizontal flow velocities (~2-7 m a-1) are up to two orders of magnitude lower than those observed on the adjacent RIS and northern MIS and there is negligible input from these ice shelves. This indicates that the SMIS is an independent ice shelf characterized by its wind-driven glaciologic regime and thus is not an analogue for the neighbouring RIS. In addition, the SMIS is buffered from potential collapse by the MIS and the surrounding land masses, and, therefore, will not respond to climate change in the same way as the exposed ice shelves that surround the rest of the continent.

xiii, 238 p. : ill., maps (some fold.) ; 30 cm. + 1 CD-ROM.

2005Clifford

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