|Alley et al. have addressed or corrected some of my comments regarding data processing and error analysis.|
Nevertheless, I still have concerns where the authors provided inadequate responses to my comments and I would still recommend major revisions to address them.
First, regarding the datasets used for the analysis, the authors explained that they are not using published NSIDC datasets to complete the period 2000-2012 because the resolution is too coarse (1km) compared to their 500m sampling resolution. I would like to point out that if their sampling resolution is 500m, the true spatial resolution of displacement maps obtained from MODIS are certainly much coarser. Typically, the native resolution of MODIS is 250m, which would mean that cross-correlation from PyCorr is done on 2x2 pixels subimages to match the final reported resolution, which seems unrealistic, if not impossible. In addition, this NSIDC time-series https://nsidc.org/data/NSIDC-0545/versions/1 provided maps in 2000, 2006-2013 at a sampling resolution of 450 m. While I agree that the period 2001-2005 is not covered in the dataset and that MODIS could be useful on the ice shelf to bring additional information, I would still think that this external dataset would have proven useful.
Thus, even after the review, I am not convinced by the MODIS result, which also casts doubt on the strain rate analysis. It is clear that the results obtained from MODIS are wrong in many places and remain fuzzy and patchy in others. I have attached the 2006 velocity map at 450 m resolution published by NSIDC, using the exact same color coding between 0 and 3 m/day that in Figure 4, so that the maps can be compared with the result from 2005-2006 in Figure 4 from the authors. The 2000-2001 and 2005-2006 speed maps from Alley et al. indicate that the ice is not moving upstream of the GL but also near the GL on floating ice. One clear example of this issue is the main ice tongue not moving near the GL in 2005-2006 while it should be moving at 2 km/yr or more than 5 m/day. The resulting strain maps calculated from these erroneous displacement maps are therefore also erroneous. Abnormally high strain rates are visible near the GL in 2000-2001 and 2005-2006, but still are highlighted (dashed black ovals in figure 4 for example) as features showing the evolution of strain on TEIS. This sensor-dependent issue is also evident in Figure 3 near the GL and on the grounded ice where the patterns of speed and strain change as soon as the authors include Sentinel1 results. As mentioned, this also raises questions about the quality of data obtained further from the grounding line and the interpretation that can be made from these very uncertain measurements.
At minimum, the authors should try to filter out the maps from 2000 and 2012 for spurious measurements, and state the real resolution of their mapping with MODIS. With the filtered and correct speed maps, they could then correct the lagrangian elevation changes, correct the strain rate calculation by updating Figure 2, Figure 3 and Figure 4, especially near the GL and on grounded ice, and adjust, if needed, their interpretation of the evolution of the strain on TEIS. I believe that it is important that the primary data source (ice displacement) is properly and correctly established, otherwise all the other observables (strain, melt) will be wrong and misinterpreted.
My second remark concerns the 1996 and 2000 grounding line (GL) from InSAR. I would strongly suggest adding it in the manuscript. Not adding the 1996 GL because it does not overlap their analysis is questionable, but it is their choice. Nevertheless the InSAR grounding line has also been mapped in 2000 which is part of their analysis. In addition, the 2004 grounding line seems to be collected between 1999 and 2003 rather than 2004 as stated here https://www.usap-dc.org/view/dataset/609489 or https://nsidc.org/data/nsidc-0489. Please clarify at which date or period (or the source if not ASAID from Bindschadler et al. (2011)) is their 2004 GL in Figure 1. In the figure above, I plotted the GL from ASAID (Bindschadler et al. 2011) as a thick dark grey line and from InSAR as thin colored lines. It appears not only that the ASAID GL seems off by several kilometers in many places but also that having the complete evolution from 1996 to 2017 does not seem to be less relevant to their analysis.
Finally, the authors mentioned in their responses that the lagrangian analysis for calculating elevation changes requires a gridded dataset, which I believe is not true. There are many studies published using lagrangian approach on non-gridded datasets such as ERS, ENVISAT, IceSAT or CryoSAT (Adusumilli et al. 2020; Moholdt et al. 2014), some of them would have had sufficient resolution to capture the TEIS evolution (Gourmelen et al. 2017).
Adusumilli, S., Fricker, H.A., Medley, B. et al. Interannual variations in meltwater input to the Southern Ocean from Antarctic ice shelves. Nat. Geosci. 13, 616–620 (2020). https://doi.org/10.1038/s41561-020-0616-z
Bindschadler, R., Choi, H., Wichlacz, A., Bingham, R., Bohlander, J., Brunt, K., Corr, H., Drews, R., Fricker, H., Hall, M., Hindmarsh, R., Kohler, J., Padman, L., Rack, W., Rotschky, G., Urbini, S., Vornberger, P., and Young, N.: Getting around Antarctica: new high-resolution mappings of the grounded and freely-floating boundaries of the Antarctic ice sheet created for the International Polar Year, The Cryosphere, 5, 569–588, https://doi.org/10.5194/tc-5-569-2011, 2011.
Moholdt, G., Padman, L., and Fricker, H. A. (2014), Basal mass budget of Ross and Filchner-Ronne ice shelves, Antarctica, derived from Lagrangian analysis of ICESat altimetry, J. Geophys. Res. Earth Surf., 119, 2361– 2380, doi:10.1002/2014JF003171.
Gourmelen, N., Goldberg, D. N., Snow, K., Henley, S. F., Bingham, R. G., Kimura, S., … van de Berg, W. J. (2017). channelized melting drives thinning under a rapidly melting Antarctic ice shelf. Geophysical Research Letters, 44, 9796– 9804. https://doi.org/10.1002/2017GL074929