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

Abstract

Abstract. We use repeat-pass SAR data to produce detailed maps of surface motion covering the glaciers draining into the former Larsen B ice shelf, Antarctic Peninsula, for different epochs between 1995 and 2013. We combine the velocity maps with estimates of ice thickness to analyze fluctuations of ice discharge. The collapse of the central and northern sections of the ice shelf in 2002 led to a near-immediate acceleration of tributary glaciers as well as of the remnant ice shelf in Scar Inlet. Velocities of the glaciers discharging directly into the ocean remain to date well above the velocities of the pre-collapse period. The response of individual glaciers differs and velocities show significant temporal fluctuations, implying major variations in ice discharge and mass balance as well. Due to reduced velocity and ice thickness the ice discharge of Crane Glacier decreased from 5.02 Gt a−1 in 2007 to 1.72 Gt a−1 in 2013, whereas Hektoria and Green glaciers continue to show large temporal fluctuations in response to successive stages of frontal retreat. The velocity on Scar Inlet ice shelf increased two- to three fold since 1995, with the largest increase in the first years after the break-up of the main section of Larsen B. Flask and Leppard glaciers, the largest tributaries to Scar Inlet ice shelf, accelerated. In 2013 their discharge was 38%, respectively 45%, higher than in 1995.

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

“…A smaller increase in surface velocities is modeled for Scar Inlet, and little change is seen for its tributary glaciers (Starbuck, Leppard, and Flask). This corresponds well to observations of an immediate impact on the stress field through rift formation and acceleration of Scar Inlet, and a smaller and delayed signal in observed surface velocities for its tributary glaciers [Wuite et al, 2015]. The work of Khazendar et al [2015] has shown that the limited response of Leppard and Flask Glaciers is likely related to a reduction in buttressing by the Scar Inlet.…”

“…This justifies the application of an instantaneous ice front perturbation in the model. The earliest observations of glacier velocities after the collapse date from December 2003, i.e., less than 2 years after the event [Wuite et al, 2015]. During this period, Hektoria and Green Glaciers increased their center line speed from about 365 m a −1 at the 1995 grounding line to more than 2000 m a −1 (or a sixfold increase) in 2003, while the grounding line retreated by several kilometers.…”

“…This study was aided by the recent release of a detailed surface velocity map of the LBIS and all its tributary glaciers for the period late 1995 to early 1996, i.e., more than 6 years prior to the collapse of the ice shelf [Wuite et al, 2015]. The study reanalyzed ERS1-2 repeat-pass Synthetic Aperture Radar data using interferometric techniques to obtain a velocity map with complete coverage of the area at 50 m resolution.…”

“…Good satellite coverage before, during, and after the disintegration, complemented by ground-based measurements, made this one of the best documented large-scale events in recent history of the cryosphere. Observations of surface velocities and elevation showed that glaciers previously feeding the ice shelf (Figure 1), accelerated and thinned [Scambos et al, 2004;Rignot et al, 2004;Hulbe et al, 2008;Rott et al, 2011;Shuman et al, 2011], leading to an overall mass loss of about 8 Gt a −1 from 2001 to 2010 [Scambos et al, 2014] and an increased discharge of grounded ice into the ocean, which is still ongoing today [Berthier et al, 2012;Wuite et al, 2015]. The acceleration, thinning, and associated grounding line retreat has been complex in behavior and highly variable in time and space, with some tributaries reacting rapidly, others with delay, and some hardly at all [Scambos et al, 2014;Wuite et al, 2015;Khazendar et al, 2015].…”

“…During the period since the collapse of the LBIS, numerical ice flow models have become increasingly more advanced in describing the observed dynamical changes of the Antarctic Ice Sheet, and their performance has been evaluated in a series of benchmark tests [Pattyn et al, 2012[Pattyn et al, , 2013. In particular, key physical processes [Wuite et al, 2015]. Blue lines indicate the ice front location for different times between 1995 and 2009; the thick black line delineates the 1995 grounding line location; thin black lines outline the drainage basins for the different tributaries , and names of the most prominent glaciers are listed.…”