Interferometric analysis of the deformation pattern of the northern Larsen Ice Shelf, Antarctic Peninsula, compared to field measurements and numerical modeling

Abstract

The motion field of the northern Larsen Ice Shelf, Antarctic Peninsula, was analyzed using radar interferometry in combination with field measurements and finite-element model calculations. The ice shelf between Jason Peninsula and Seal Nunataks has been in steady retreat since January 1995. Model calculations suggest that the ice shelf is in a stage of irreversible retreat since the last calving events in summer 1998/99. The interferometric analysis is based on synthetic-aperture radar data of the tandem mission of European remote-sensing satellites ERS-1 and –2 in austral spring 1995. The phase contributions due to tidal motion were estimated from the vertical displacement at those parts of the grounding zone where the horizontal motion is close to zero" in order to separate the vertical and horizontal motion components over the ice shelf. Satellite-derived velocities compare well with the long-term field measurements along a transverse and a longitudinal profile. The real interferograms and synthetic interferograms, calculated from model velocities, show reasonable agreement over the main parts of the ice shelf, but differ in the boundary zones where the details are not resolved by the model.

Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013

“…GPS measurements at stakes on Larsen B located 50 km downstream of these glaciers showed flow acceleration in the order of 10 % between 1994 and 1999 (Rack, 2000). This indicates that also the southern sections of Larsen B Ice Shelf had weakened mechanically previous to the disintegration event in 2002, as reported for the northern and central sections Rack and Rott, 2004). Our analysis of substantial flow acceleration and development of rifts, evident in satellite data of 2004, implies that the break-up had a near immediate impact on the stress field of the ice shelf.…”

“…The basin outlines inland were provided by A. Cook based on the ASTER derived Antarctic Peninsula DEM (API-DEM) (Cook et al, 2012). shelf collapse the frontal regions of HGE retreated quickly (Rack and Rott, 2004;Scambos et al, 2004), suggesting that they were lightly grounded and sensitive to changes in iceshelf buttressing. The ice shelf collapse resulted in the progressive breakup of increasingly large areas of grounded ice concomitant with acceleration of ice flow and dynamic thinning, amounting to a total retreat of 174 km 2 by January 2012.…”

“…Progressive retreat culminated in the final disintegration of the Larsen A Ice Shelf in January 1995 and of the northern and central sections of the Larsen B Ice Shelf in March 2002 (Rott et al, 1996;Rack and Rott, 2004;Glasser and Scambos, 2008). The glaciers flowing from the Antarctic Peninsula plateau, previously feeding the ice shelves, became tidewater glaciers.…”

Modeling the instantaneous response of glaciers after the collapse of the Larsen B Ice Shelf

“…Despite signs of mechanical weakening of the ice shelf prior to its collapse [Rack et al, 2000], the dominant loss of buttressing for the tributary glaciers was near-instantaneous, as the main part of the ice shelf broke away over the course of a few weeks in February 2002. This justifies the application of an instantaneous ice front perturbation in the model.…”

“…In order to correct this uncertainty and to obtain a surface elevation that is closer to the (unobserved) precollapse values, we applied a correction to the API-DEM, requiring the ice upstream of the 1995 grounding line to be at or below floatation. The grounding line position was taken from the ERS InSAR analysis of Rack et al [2000]. This correction raised the surface by up to 60 m for Crane Glacier (the geographical location and names of all glaciers are listed Figure 1) and up to 80 m for Hektoria-Green-Evans Glaciers over an area extending up to 5 km upstream of the grounding line.…”