In today’s Academic Minute, Dr. Joe MacGregor of the University of Texas at Austin explains the mechanics of the fracturing currently plaguing the ice sheet of Antarctica.
Joe MacGregor is a post-doctoral fellow at the Institute for Geophysics at the University of Texas at Austin. His broad research interests include glacier and ice-sheet dynamics, subglacial conditions and the geology of Greenland and Antarctica, ice-sheet-climate interactions, climate change, and extraterrestrial ice masses. He holds a Ph.D. from the University of Washington.
Dr. Joe MacGregor – Fracturing of the Antarctic Ice Sheet
Antarctica is changing much more rapidly than anyone would have predicted twenty years ago. Many Antarctic glaciers that discharge ice into the sea have accelerated significantly. More and more, glaciologists such as myself are finding that this acceleration originates at the floating ice shelves that surround much of the continent. These thick ice shelves themselves don’t affect sea level, just like a melting ice cube in your glass doesn’t change the water level, but the ice shelves do hold back the grounded glaciers, which can affect sea level.
There’s now good evidence that a root cause of this acceleration is melting underneath the ice shelves, which in turn is related to changing wind patterns and warming oceans. Nowhere in Antarctica are these changes more evident, and perhaps nowhere is more vulnerable to such changes, than the Amundsen Sea Embayment.
We examined in detail nearly forty years of satellite imagery of the coast of the Amundsen Sea Embayment. What we found is that its ice shelves are essentially tearing apart at their seams, which are where they meet either rocky bay walls or slower-flowing ice. Cracks that propagate through the whole of the ice shelves formed along the seams, causing them to lose their grip, so to speak. As they lost this grip, resistance to ice flow was lost, which caused additional acceleration.
So, what started out as just ice-shelf melting became something more insidious. Eventually the ice shelves will crack through their seams entirely, but until they do so, acceleration will likely continue. In fact, there are several big cracks present today that suggest that more tearing apart is on the way. The challenge now is to reproduce our observations in computer models and improve predictions about future changes in Antarctica.