Polar Seminar: The impact of mechanical weakening of ice shelves on the stability of a marine ice sheet

03/18/2014 - 2:00pm to 3:00pm

Christopher Borstad
Postdoctoral Researcher, NASA Jet Propulsion Laboratory, Pasadena, CA

Title: The impact of mechanical weakening of ice shelves on the stability of a marine ice sheet
Abstract: The majority of the Antarctic ice sheet drains to the ocean through floating ice shelves, most of which provide some measure of buttressing against the discharge of ice into the ocean. In many sectors of Antarctica ocean-driven basal melting is thinning ice shelves, which reduces buttressing while at the same time making ice shelves more susceptible to fracturing. As a thinning ice shelf becomes weakened by fractures, it might be expected to provide even less buttressing at the grounding line, allowing increased flow speeds, further weakening, and so on in a possible feedback loop. In this way the mechanical weakening of ice shelves may contribute to accelerating the retreat of a marine ice sheet. However, to date only qualitative statements have been made about possible feedbacks between ice shelf fracturing, ice shelf buttressing, and grounding line stability. Here, I outline recent research into the role of mechanical weakening of Pine Island Glacier's ice shelf on the evolution of this glacier using a time series of remote sensing data assimilated in an ice sheet model. I apply principles of continuum damage mechanics to quantify the softening influence of fractures on the stress balance in the ice shelf. Although thinning of the ice shelf is confirmed to be the dominant cause of the increase in glacier speed in recent decades, thinning alone is insufficient to explain the full speed up. The shear margins of the ice shelf have weakened and damage has progressively localized, and these rheological changes must be superimposed on top of the thinning signal to reproduce the observed changes in this important glacier system. 
For more information on this event, contact: 
Matthew Siegfried
Event Calendar: 
4301 Revelle