GPS-derived strain rates on an active ice shelf rift

Ice shelves are important components of the Antarctic ice sheet due to their ice-ocean-atmosphere interface and vulnerability to global increases (or decreases) in atmospheric and oceanic temperatures. The development of rifts, which are fractures that penetrate through the entire ice shelf thickness, precede large tabular iceberg detachment and can lead to ice shelf break-up. Changes in strain rates on an active propagating rift system on the Amery Ice Shelf, East Antarctica are determined using in-situ Global Positioning System (GPS) measurements. Results for the 2002/03 Antarctic summer period (Dec-Feb) confirm previous observations by [2] that rift propagation occurs in episodic bursts separated by several days. Transverse-to-flow (i.e. parallel-to-rift) strain rates exceed longitudinal-to-flow (i.e. normal-to-rift) rates by up to a factor of 5 and maximum principal strain rates around the rift tip vary from 12 to 21 [x 10-3/yr]. A rotation in the direction of the principal strain is evident around the rift tip, indicating a change in the mechanics of rift fracture. It is demonstrated that cumulative sum analysis [12], obtained by differencing a pair of residual baseline time series situated approximately normal and parallel to the rift, is an effective method to detect small baseline length changes.