Ice Sheet Model Simulations of North Atlantic Ice Rafting Events: Rogue Ice Streams or Submissive Calving Margins?

D R MacAyeal (University of Chicago, Chicago, IL 60637; ph. 773-702-8027; fax. 773-702-8198; Internet: drm7@midway.uchciago.edu)

The old idea that a few rogue ice streams can be responsible for the North Atlantic's IRD record without forcing by an external climate agent (e.g., an atmospheric or oceanic climate pattern that persists even in the absence of ice sheets) appears to be discredited by virtue of three things: the global nature of climate change coordinated with IRD events, the mixing of IRD sources during events, and new evidence of sub-millenial scale climate variation during Holocene and other low-ice-volume periods. Nevertheless, ice-stream instability remains and important unresolved player in the phenomenon, as evidenced by continuing model studies (e.g., Marshall and Clarke, 1997) which show how rogue ice streams can oscillate over Heinrich Event time periods. I propose to examine the role of rogue ice-stream dynamics in circumstances where the primary forcing mechanism for IRD events is the external climate. This examination will involve a series of experiments using a finite- element model of ice-sheet dynamics which is capable of resolving (at the grid scale) ice streams. The model runs have not yet been completed, so the results are unknown at the time of writing.