Abstract
AbstractFifteen synthetic aperture radar (SAR) images of the Ronne Ice Shelf (also referred to as the Filchner-Ronne Ice Shelf), Antarctica, obtained by the European remote-sensing satellites ERS-1 and -2, are used to study ice-shelf dynamics near two ends of the iceberg-calving front. Interferograms constructed from these SAR images are used to resolve the ice-shelf displacement along several directions in response to both ocean tide and long-term creep flow. Tidal motion is separated from creep flow using differential interferometry, i.e. two or more interferograms in which fringe patterns common to all are predominantly associated with creep flow. Creep-flow velocities thus determined compare well with prior ice-shelf velocity surveys. Using these data, we studied the influence of large-scale rifts, ice rises and coastal separation on the ice-shelf flow. Many of the large rifts that appear to form the boundaries where tabular icebergs may eventually detach from the ice shelf are filled with a melange of sea ice, ice-shelf debris and wind-blown snow. The interferograms show that this melange tends to deform coherently in response to the ice-shelf flow and has sufficient strength to trap large tabular ice-shelf fragments for several decades before the fragments eventually become icebergs. In many instances, the motion of the tabular fragments is a rigid-body rotation about a vertical axis that is driven by velocity shear within the melange. Tfhe mechanical role of the rift-filling melange may be to bind tabular ice-shelf fragments to the main ice shelf before they calve. This suggests two possible mechanisms by which climate could influence tabular iceberg calving. First, spatial gradients in oceanic and atmospheric temperature may determine where the melange melts and, thus, the location of the iceberg-caking margin. Second, melting or weakening of ice melange as a consequence of climate change could trigger a sudden or widespread release of tabular icebergs and lead to rapid ice-shelf disintegration.
Highlights
Among th e principal processes that influe nce Antarctic icesheet stabilit y a re rifting and tab ul a r icebe rg ca lving a long the seawa rd margins of the icc shelves
Our interferograms suggest that ice-shelf rifting, a longte rm process th a t c ulminates in tabular iceberg rel ease, is stro ngly influe nced by sea ice a nd other t ypes of ice, which fill th e rift
The mos t striking aspect of ice-shelf behavior revea led by th e interferograms of the FRIS studied here concerns the development of ice-shelf rifts, which e\'Cntua lly become tab ul a r iceberg detac hment boundaries
Summary
Among th e principal processes that influe nce Antarctic icesheet stabilit y a re rifting and tab ul a r icebe rg ca lving a long the seawa rd margins of the icc shelves. Sanderson's (1979) hypoth es is is supported by the fact th a t th e Filchn e r- Ronne, Ross a nd Am ery ice shelves termin ate where th e coastlin e te nd s to di\·erge It d oes not, add ress o ther factors th a t a rc necessary for iceberg ca lving, such as th e formatio n o f rifts a long which ta bul ar icebe rgs detac h fro m the m ain ice sh elf; tidal fl ex ure, coasta l ro ug hness a nd stra in heating. As a long HIR , th e tab ul a r ice-shelf frag m e nts appea r to be bound together by sea ice a nd wind-blown snow to fo rm a mela nge th at covers the sea surface within th e rifts. Th e interferogr a m s of LC a re expec ted to reveal a n equ a l mi xture of ice-shelf tidal m otion a nd creep fl ow
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