ICE STREAMS STOP AND START

Flow features on the surface of the Ross Ice Shelf, West Antarctica, record at least two episodes of ice stream stopping and reactivation within the last 1000 years. These events are documented using maps of streaklines emerging from individual ice streams and a relative chronology is established using numerical models of ice flow. In addition to the recent stoppage of Kamb Ice Stream, we find that Whillans Ice Stream ceased rapid flow about 850 years ago and restarted about 400 years later and MacAyeal Ice Stream either stopped between 800 and 700 years ago, restarting about 150 years later. A Kamb Ice Stream cycle prior to the current shut down is possible, but the evidence is challenging to interpret.

Streakline deformation (folding) arises from a small suite of scenarios, all of which involve large variations in ice stream discharge and ice rises, locations where floating ice runs aground. Variations in ice thickness associated with ice stream discharge cycles yield rapid grounding and ungrounding in the broad ice plain across which the streams discharge into the floating ice shelf. These transients may be thought of as migration of the ice sheet grounding line and the models used to interpret past discharge events are also used to investigate this history. Unsurprisingly, grounding and ungrounding are intimately connected to bathymetry in the ice stream outlet region, emphasizing the three dimensional nature of the the problem.