Abstract
ABSTRACTWe use satellite radar interferometry to investigate changes in the location of the Petermann Glacier grounding line between 1992 and 2011. The grounding line location was identified in 17 quadruple-difference interferograms produced from European Remote Sensing (ERS)-1/2 data – the most extensive time series assembled at any ice stream to date. There is close agreement (20.6 cm) between vertical displacement of the floating ice shelf and relative tide amplitudes simulated by the Arctic Ocean Dynamics-based Tide Model 5 (AODTM-5) Arctic tide model. Over the 19 a period, the groundling line position varied by 470 m, on average, with a maximum range of 7.0 km observed on the north-east margin of the ice stream. Although the mean range (2.8 km) and variability (320 m) of the grounding line position is considerably lower if the unusually variable north-east sector is not considered, our observations demonstrate that large, isolated movements cannot be precluded, thus sparse temporal records should be analysed with care. The grounding line migration observed on Petermann Glacier is not significantly correlated with time (R2 = 0.22) despite reported ice shelf thinning and episodes of large iceberg calving, which suggests that unlike other ice streams, on the south-west margin of the Greenland ice sheet, Petermann Glacier is dynamically stable.
Highlights
Ice losses from Greenland and Antarctica have increased rapidly over recent decades – by 278 and 148%, respectively. since 1992 – and the most pronounced changes have occurred in places where the ice sheets are grounded well below sea level (Shepherd and others, 2012)
There is close agreement between the magnitude of the ice-shelf relative displacement and the size of differential tides predicted by the Arctic Ocean Dynamics-based Tide Model 5 (AODTM-5) model, with positive or negative displacements recorded at times of high and low differential tides respectively
The change in slope is most abrupt at times of high relative displacement, the transition between grounded and floating ice remains distinct in all profiles, allowing the grounding line to be located as the landward break in surface slope across the zone of iceshelf flexure (Rignot and others, 1996)
Summary
Ice losses from Greenland and Antarctica have increased rapidly over recent decades – by 278 and 148%, respectively. since 1992 – and the most pronounced changes have occurred in places where the ice sheets are grounded well below sea level (Shepherd and others, 2012). Have been employed to date: (1) the detection of change in surface shading caused by the break in ice-sheet surface slope in optical imagery (Scambos and others, 2007; Bindschadler and others, 2011), (2) the detection of tidal motion in quadruple difference interferometric synthetic aperture radar (QDInSAR) observations (Goldstein and others, 1993) and (3) repeat satellite altimeter measurements (Fricker and Padman, 2006). It has been shown (Rignot, 1998a) that the technique of QDInSAR is capable of detecting grounding lines with fine (30 m) spatial resolution and with high precision. The most useful QDInSAR data were acquired during periods when the two European Remote Sensing (ERS) satellites were orbiting in a 3 d repeat cycle between 1991/92, 1993/94 and in 2011; and in a 1 d repeat cycle between 1995/96
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