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History and evolution of the Siple Coast ice stream system



Participants:

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 millenia. Also, we are interested in understanding what controls the positions of ice streams. In particular, what role to the interstream ridges play in controlling ice flow in the 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 curvilinear features surrounding ISC may mark the former ice stream boundaries.



Project highlights:



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 2.5 km that slides 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 layeris 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 assymetric 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 because of the absence of near-surface crevassing.



Eastern edge of Ridge BC




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 was obtained. We found some disturbed layers at roughly 54 m depth on the end of the ridge where no surface expression indicated a disturbance. The GPR data helped us to determine the extent of this area. Again, double click on images 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 the 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 speeds fast enough to cause crevassing and may represent an ephemeral onset region.



The bounday for this area is very sharp. on the left is GPR data acquires 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 images in this area and we believe that it is an ice stream that stopped several hundred years ago.






Published/Presented Results:

G. Catania, T. Scambos, H. Conway, and C. Raymond, in press, The sequential stagnation of Kamb Ice Stream, West Antarctica, Geoph. Res. Lett.

G. Catania, H. Conway, C. Raymond and T. Scambos, 2006, Evidence for floatation or near-floatation in the mouth of Kamb Ice Stream, West Antarctica prior to stagnation, J. Geophys. Res., 111, F01005, doi:10.1029/2005JF000355.

C. Raymond, G. Catania, N. Nereson and K. van der Veen, 2006, Bed radar reflectivity across the north margin of Ice Stream B2 and implications for margin processes, J. Glaciol., 52(176), 3-10.

G. Catania, H. Conway, C. Raymond and T. Scambos, 2005, Surface morphology and internal layer stratigraphy in the downstream end of Kamb Ice Stream, West Antarctica, J. Glaciol., 51(174), 423-431.

H. Conway, G. Catania, C. Raymond, A. Gades, T. Scambos, H. Engelhardt, 2002, Switch of flow direction of an Antarctic ice stream, Nature, 419(6906), 465-467.
 
G. Catania, H. Conway, A. Gades, C. Raymond and T. Scambos, 2001, GPR and RES reveal disturbed internal stratigraphy on Ridge B/C, Antarctica, 8th Annual WAIS Workshop.

T. Scambos, H.Conway, C. Raymond, A. Gades, G. Catania, M. Fahnestock, 2001, The last thousand years of ice flow in the Siple Coast, 8th Annual WAIS Workshopp.

H. Conway, G. Catania, A. Gades, C. Raymond and T. Scambos, 2001, Paleo-Ice Stream C0, 8th Annual WAIS Workshop.

G. Catania, H. Conway, C. Raymond and T. Scambos, 2002, Duckfoot and Goosefoot: What happened at the lower end of Ice Stream C, 9th Annual WAIS Workshop.

G. Catania, H. Conway, C. Raymond and T. Scambos, 2004, Ungrounded conditions in the mouth of Kamb Ice Stream?, 11th Annual WAIS Workshop.

G. Catania, H. Conway, C. Raymond and T. Scambos, 2003, Flat ice terrain near the mouth of Kamb Ice Stream, 10th Annual WAIS Workshop.

G. Catania, T. Scambos, H. Conway, C. Raymond, C. Hulbe, 2005, Century-scale Ice Stream Variability and Stability: A case study of Kamb Ice Stream, West Antarctica, AGU Fall Meeting