Flow history of the Ross Sea Ice Streams

Participants:

Howard Conway, University of Washington
Maurice Conway, Thames, New Zealand
Tony Gades, University of Washington
Charlie Raymond, University of Washington
Ted Scambos, NSIDC(University of Colorado)
Ginny Catania, University of Washington
 
 

Project Goals:

This project hopes to understand the nature of the "scar" features surrounding Ice Stream C in order to best interpret the ice flow history in the last millennia.  Also, we are interested in understanding what controls the positions of ice streams. In particular, what role do the interstream ridges play in controlling ice flow in this area.  Finally, we hope to use this information to infer ice sheet thickness changes over the last few centuries.  The RAMP image below shows our field area.  Stagnant Ice Stream C is located in the center of the image.  The shear margins of Ice Stream B show up as bright linear features.  The many curvi-linear features surrounding ISC may mark the former ice stream boundaries.

Project Highlights/ Initial Results:
 

Some of the more interesting features discovered during the 2000 field season were located on the flat ice terrain on the downstream portion of Ridge BC.  A RAMP image of DnRBC with the scar feature in question is shown above.  Radar profiles collected along the blue line near the middle of the image are shown below.  The purple line shows where radar data were collected by Retzlaff and Bentley (1993).  Double click on any of the images below to get a better look at the data:
 

RES profile along the blueline in the center of the image above.  Ridge BC is to the left. Two curvilinear "scar" features were crossed in this profile, one at 2.5km that sidles alongside Ridge BC, and another at the right hand side which represents the ISC margin.

This RES image gives a detailed look at the internal layers across the "scar" feature marked by the red arrow.  Ridge BC is on the left and ISC is on the left. Characteristic to this area of flat ice is a trough feature located to the right of a strong diffractor (this time asymmetric is amplitude).  We do not yet understand the nature of this feature but believe that it is not a former Ice Stream C margin because of the absence of near-surface crevassing.

 

This is yet another RAMP image showing the upstream (or Eastern end) of Ridge BC.  The thick red and blue lines are where GPR and RES data were obtained.  The thinner blue lines are where only GPR data was obtained.  We found some disturbed layers at roughly 54m depth on the end of the ridge where no surface expression indicates a disturbance.  The GPR data helped us to determine the extent of this area.  Again, double click on the images below to get a better look.
 
 

	These data were acquired along the red line in the above RAMP image of the upstream end of RBC. On left are the flat layers of the ridge and on the right is the ISC margin indicated by shallow disturbed layers beginning at the rightmost red arrow. Between ISC and the flat layers on the ridge lies an area with disturbed deep internal stratigraphy and diffraction returns in the shallow subsurface. This area probably did not approach streaming speeds but moved at speedsfast enough to cause crevassing and may represent an ephemeral onset region.
	The boundary for this area is very sharp.  On the left is GPR data acquired across this disturbed zone.  You can see flat layers at depth that give way (at the red arrow) to a disturbed area.  You can see faint wave like patterns in this area which may indicate sagging snow bridges over crevasses.
	This RES profile was acquired along the thick blue line in the RAMP image of the Eastern end of RBC. You can see faint flowstripes on the RAMP image in this area and we believe that it is an ice stream that stopped several hundred years ago.

 

Published/PresentedResults:

GPR and RES reveal disturbed internal stratigraphy on Ridge B/C, Antarctica G. Catania, H. Conway, A. Gades, C. Raymond and T. Scambos, 2001WAIS Conference, Maryland.

Paleo-Ice Stream C0, H. Conway, G. Catania, A. Gades, C. Raymond and T. Scambos, 2001 WAIS Conference, Maryland.

The last thousand years of ice flow in the Siple Coast, T. Scambos, H.Conway, C. Raymond, A. Gades, G. Catania, M. Fahnestock, 2001 WAIS Conference, Maryland.

Switch of flow direction in an Antarctic ice stream, 2002, H. Conway, G. Catania, C. Raymond, A. Gades, T. Scambos & H. Engelhardt, Nature, (419), 465-467.

Bed-reflectivity beneath inactive ice streams in West Antarctica, 2003, G. Catania, H. Conway, A. Gades, C. Raymond and H. Engelhardt, Annals of Glaciology, (37).