The control of an uncharted pinning point on the flow of an Antarctic ice shelf

Abstract

ABSTRACT. Antarctic ice shelves are buttressed by numerous pinning points attaching to the otherwise freely-floating ice from below. Some of these kilometric-scale grounded features are unresolved in Antarctic-wide datasets of ice thickness and bathymetry, hampering ice flow models to fully capture dynamics at the grounding line and upstream. We investigate the role of an 8.7 km 2 pinning point at the front of the Roi Baudouin Ice Shelf, East Antarctica. Using ERS interferometry and ALOS-PALSAR speckle tracking, we derive, on a 125 m grid spacing, surface velocities deviating by −5.2 ± 4.5 m a −1 from 37 on-site global navigation satellite systems-derived velocities. We find no evidence for ice flow changes on decadal time scales and we show that ice on the pinning point virtually stagnates, deviating the ice stream and causing enhanced horizontal shearing upstream. Using the BISICLES ice-flow model, we invert for basal friction and ice rigidity with three input scenarios of ice velocity and geometry. We show that inversion results are the most sensitive to the presence/absence of the pinning point in the bathymetry; surface velocities at the pinning point are of secondary importance. Undersampling of pinning points results in erroneous ice-shelf properties in models initialised by control methods. This may impact prognostic modelling for ice-sheet evolution in the case of unpinning.

Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

“…The velocities are mosaicked and gridded to a 125 m posting and are based on images from the European Remote Sensing satellites (ERS 1/2) from 1996 and the Advanced Land Observing System Phased Array type L-band Synthetic Aperture Radar (ALOS-PALSAR) from 2010. As shown in Berger et al (2016), comparison with on-site measurements collected in 1965-1967 and 2012-2014 yields no evidence of prominent changes in the ice velocities over the last decades, which supports the combination of data from different dates. The velocity mosaic covers 75 % of our area of interest (dashed line in Fig.…”

“…The high-resolution velocity dataset from Berger et al (2016) is available via https://doi.pangaea.de/10.1594/ PANGAEA.883284 (Berger et al, 2017a). The LBMB, hydrostatic thickness and elevation mosaics are available via https:// doi.pangaea.de/10.1594/PANGAEA.883285 (Berger et al, 2017b).…”

The sensitivity of West Antarctica to the submarine melting feedback

“…We examine the sensitivity to reducing the minimum thickness in the supporting information. To include the buttressing effect of unresolved ice rises [Berger et al, 2016], we allowed our inversion for basal drag to produce nonzero values on floating ice, where this is needed to match the observed surface velocities. Later we consider the consequences of removing drag from these unresolved ice rises, to simulate what would happen if some proportion of them went afloat.…”

Recent rift formation and impact on the structural integrity of the Brunt Ice Shelf, East Antarctica

“…In subsequent decades, the BIS gradually readvanced and reestablished contact with the bedrock at the MIR, whilst velocities decreased to pre-1970 levels (Gudmundsson et al, 2017). This cycle of internal dynamical change controlled by calving-induced unpinning and subsequent regrounding at the MIR is arguably not a unique phenomenon, as many ice shelves around Antarctica, and in particular in Dronning Maud Land, are controlled by the presence of one or several pinning points (Matsuoka et al, 2015;Fürst et al, 2015;Favier et al, 2016;Berger et al, 2016). However, the long observational record and the relatively short calving frequency on the order of decades makes the BIS an ideal location to study this cycle.…”