Abstract
Abstract. We present the results of mapping the limit of the tidal flexure (point F) and hydrostatic equilibrium (point H) of the grounding zone of Antarctic ice shelves from CryoSat-2 standard and swath elevation data. Overall we were able to map 31 % of the grounding zone of the Antarctic floating ice shelves and outlet glaciers. We obtain near-complete coverage of the Filchner–Ronne Ice Shelf. Here we manage to map areas of Support Force Glacier and the Doake Ice Rumples, which have previously only been mapped using break-in-slope methods. Over the Ross Ice Shelf, Dronning Maud Land and the Antarctic Peninsula, we obtained partial coverage, and we could not map a continuous grounding zone for the Amery Ice Shelf and the Amundsen Sea sector. Tidal amplitude and distance south (i.e. across-track spacing) are controlling factors in the quality of the coverage and performance of the approach. The location of the point F agrees well with previous observations that used differential satellite radar interferometry (DInSAR) and ICESat-1, with an average landward bias of 0.1 and 0.6 km and standard deviation of 1.1 and 1.5 km for DInSAR and ICESat measurements, respectively. We also compared the results directly with DInSAR interferograms from the Sentinel-1 satellites, acquired over the Evans Ice Stream and the Carlson Inlet (Ronne Ice Shelf), and found good agreement with the mapped points F and H. We also present the results of the spatial distribution of the grounding zone width (the distance between points F and H) and used a simple elastic beam model, along with ice thickness calculations, to calculate an effective Young modulus of ice of E=1.4±0.9 GPa.
Highlights
In Antarctica, the majority of the grounded ice sheet (74 %, Bindschadler et al, 2011) abuts floating ice shelves or outlet glaciers
We calculated the mean of tidal amplitude (Td) to obtain a single value over the observation period and only used data where −0.5 < Td < 1.5 and |Td − Td| < 0.5, where Td represents the median values of the yearly measurements per cell
The lowest standard deviations are found in the high-latitude, high-tidal-range areas of the Ross Ice Shelf and the Filchner–Ronne Ice Shelf, while over the lower-latitude areas where coverage is sparser the standard deviation is high between yearly measurements
Summary
In Antarctica, the majority of the grounded ice sheet (74 %, Bindschadler et al, 2011) abuts floating ice shelves or outlet glaciers. Break-inslope methods (Bohlander and Scambos, 2007; Bindschadler et al, 2011; Bamber and Bentley, 1994; Hogg et al, 2017) between the flat ice shelf and the grounded ice sheet allow us to map the grounding line, but in regions where there is not a clear break in slope, this technique can be unreliable or ambiguous (Bamber and Bentley, 1994; Fricker and Padman, 2006; Brunt et al, 2010; Rignot et al, 2011; Depoorter et al, 2013) It is over these regions where ice thickness does not increase rapidly across the grounding zone that grounding line retreat is most likely, and there is good spatial and temporal coverage using DInSAR techniques. The grounding line width, W (the distance between point F and H), is used, in combination with independent ice thickness measurements and the simple elastic beam model of the grounding zone to investigate its structure
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