BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:The role of pinning-points\, marine ice and subglacial channeling 
 in defining the buttressing strength of the Roi Baudouin Ice Shelf\, Antar
 ctica  - Reinhard Drews\, Université Libre de Bruxelles
DTSTART:20140627T140000Z
DTEND:20140627T143000Z
UID:TALK53206@talks.cam.ac.uk
CONTACT:Rosie Williams
DESCRIPTION:Within the coastal belt of Dronning Maud Land\, many ice shelv
 es\, which are freely floating otherwise\, reattach to localized highs in 
 the bathymetry on the ice-shelf front. These localized pinning-points exer
 t a buttressing force\, which typically slows down the ice shelves farther
  upstream. Our interest is to quantify this buttressing effect\, and to de
 termine as to whether or not\, the comparatively small pinning-points can 
 play a decisive role in defining the mass balance of tributary glaciers.\n
 \nWe consider the Roi Baudouin ice shelf\, which is laterally confined by 
 two large ice rises\, and pinned on the ice-shelf front by a small ice rum
 ple. It buttresses the western Ragnhild glacier. On the ice-shelf surface\
 , satellite imagery reveals a number of elongated surface depressions\, wh
 ich are aligned along-flow and which correspond to a sub-ice shelf channel
 ing system. We present the results of two consecutive field seasons which 
 were geared at unraveling the combined effect of ice rumple and subice-she
 lf channels on the ice shelf’s buttressing strength.\n\nAround 130 km of
  multi-frequency radar profiles map the channeling as well as the basal in
 terface of the pinning point.\nWe observe strongly dipping internal layers
  within the surface depressions and a firmly grounded ice rumple. Data fro
 m a 20 x 25 km wide GNSS strain net is extended spatially on a 50 m grid w
 ith the help of satellite derived surface velocities. Six wide-angle radar
  surveys within the research grid show that the depth-averaged density var
 ies spatially on scales that are smaller than the grid size in commonly ap
 plied Antarctic-wide firn densification models. The density variations are
  significant\, and need to be taken into account when comparing the hydros
 tatically inverted GPS thickness with the measured radar thickness.\n\nNot
 withstanding the ice-rumple’s small extent (1-2 km)\, the combined strai
 n rates show a shear zone which extends all the way back to the grounding 
 line and emphasizes the importance of pinning points in ice-shelf dynamics
 . The comparison of GPS heights with radar thickness reveals a marine ice 
 layer\, with a variable thickness\, particularly in the pinning-point’s 
 vicinity. The sub-ice shelf channels extend vertically more than half of t
 he ice thickness\, which potentially makes the channels more susceptible t
 o horizontal shearing as they approach the pinning point. The combined dat
 a set illustrates that the ice-shelf properties are non-homogeneous\, and 
 we hypothesize that this results in a spatially variable effective viscosi
 ty which needs to be taken into account in ice-flow modeling.\n\n
LOCATION:British Antarctic Survey\, Room 307
END:VEVENT
END:VCALENDAR