Mapping the grounding zone of the Amery Ice Shelf, East Antarctica using InSAR, MODIS and ICESat

Abstract

Abstract:We use a combination of satellite techniques (interferometric synthetic aperture radar (InSAR), visible-band imagery, and repeat-track laser altimetry) to develop a benchmark map for the Amery Ice Shelf (AIS) grounding zone (GZ), including its islands and ice rises. The break-in-slope, as an indirect estimate of grounding line location, was mapped for the entire AIS. We have also mapped ,55% of the landward edge and ,30% of the seaward edge of the ice shelf flexure boundary for the AIS perimeter. Vertical ice motion from Global Positioning System receivers confirms the location of the satellite-derived GZ in two regions. Our map redefines the extent of floating ice in the south-western AIS and identifies several previously unmapped grounded regions, improving our understanding of the stresses supporting the current dynamical state of the ice shelf. Finally, we identify three along-flow channels in the ice shelf basal topography, approximately 10 km apart, 1.5 km wide and 300-500 m deep, near the southern GZ. These channels, which form at the suture zones between ice streams, may represent zones of potential weakness in the ice shelf and may influence sub-ice-shelf ocean circulation.

Glacier change along West Antarctica's Marie Byrd Land Sector and links to inter-decadal atmosphere–ocean variability

“…For background, we briefly lay out the main principles of this technique. We use medium-resolution optical satellite imagery to delineate the break-in-slope across the grounding zone, otherwise known as the "inflexion point", I b , defined as the most seaward continuous surface-slope break detectable in optical satellite imagery (Scambos et al, 2007;Fricker et al, 2009). Used as a proxy for the true GL, which cannot be recovered directly from satellite remote sensing, I b appears as a clearly defined shadow-like change in on-screen pixel intensity (cf.…”

“…Such circumstances include the mapping of I b over lightly grounded ice plains, where multiple or no continuous breaks-in-slope are detectable in optical imagery; instances where the location of I b lies many kilometres landward or seaward of the true GL near ice-plains or ephemerally grounded pinning points (cf. Fricker & Padman, 2006;Fricker et al, 2009;Brunt et al, 2010; and over fast-flowing ice streams, where shallow ice-surface slopes, pronounced ice-surface flowlines, and dense crevasse fields render the location of the break-inslope ambiguous or impossible to delimit (cf. Bindschadler et al, 2011;.…”

“…Brunt et al, 2010Brunt et al, , 2011Joughin et al, 2016;Scheuchl et al, 2016). Additional confounding variables such as diurnal tidal variability and atmospheric forcing -previously recognized as important controls on GL migration over much shorter temporal baselines (Anandakrishnan et al, 2003;Fricker et al, 2009;Brunt et al, 2010) -are assumed to be negligible over the timescales we consider (cf. Milillo et al, 2017).…”

Ice-shelf basal channels in a coupled ice/ocean model

“…Along the northern edge we impose ∂U/∂y = ∂V /∂y = ∂S/∂y = ∂T /∂y = 0 as an approximation to an open (radiation) boundary condition with rapid outflow (Durran, 1999). Numerical instability can arise if V is allowed to take on negative values along the northern boundary, so this is not permitted.…”

Antarctic ice rise formation, evolution, and stability

“…Ice rumples and ice rises are common around the Antarctic Ice Sheet. For instance, they are found in the Amery Ice Shelf [Fricker et al, 2009], in the Ross Ice Shelf with the Crary and Steershead ice rises [Fahnestock et al, 2000] and Roosevelt Island [Martin et al, 2006], in the Larsen C Ice Shelf with the Bawden and Gipps ice rises [Jansen et al, 2010], and in the Ronne Ice Shelf with the Korff and Henry ice rises surrounding the Doake ice rumples [Johnson and Smith, 1997]. They are also numerous along the Dronning Maud Land (DML) coast in East Antarctica and may therefore strongly affect ice sheet stability in this region.…”