Reply on RC2

: —MSGL end 11 km from shelf break indicating LGM position. That is minimum position but not necessarily max. Make this clear. Sentence will be changed to: “Our surveys show that Mega-Scale Glacial Lineations cover most of the mouth of this trough, terminating 11 km away from the continental shelf break, indicating the most recent minimal extent of grounded ice in this region.” Sentence in line 359 will be changed as well.

Line 23-24: The sentence " Recent studies have shown that ice shelves in this region are underlain by deep glacial troughs (Nøst, 2004; Eisermann et al., 2020; Smith et al., 2020), indicating ice advanced towards outer continental shelf areas in the past." doesn't make sense. If the ice shelf has a trough under it, all it means is that grounded ice advanced as far as the modern-day ice shelf edge in the past. If showing that ice advanced towards the outer continental shelf in the past, need to say that the trough in fact extends that far, beyond the edge of the ice shelf. The MSGLs prove, that grounded ice occurred maximal 11 km from the current calving front as well as 11 km from the continental shelf. The overdeepend trough beneath Ekström is assumed to be a result of former ice stream erosion (e.g. Smith et al. 2020). Therefore, the grounded ice extended shortly before the bathymetric sill (see line 214). Floating ice, however, has probably reached across the continental shelf (Grobe andMackensen, 1992, Smith et al. 2020). Sentence will be changed to: "Recent studies have shown that ice shelves in this region are underlain by deep glacial troughs (Nøst, 2004;Eisermann et al., 2020;Smith et al., 2020), indicating that grounded ice advanced to the continental shelf in the past." Line 34 (and related to the above): how narrow is the continental shelf? "Narrow" doesn't tell much. The continental shelf is located 25 km from the current ice shelf front. As e.g. in Nøst, 2004, who as well describes the area at in the eastern Weddell Sea as narrow, we think an exact number does not really help to understand the geological setting. If interested, it can be measured in Fig. 1  Line 48: "front" of the ice shelf is not especially clear. State seaward or from edge. Sentence will be changed to: "Our study area covers the continental shelf and the sea floor under the first 50 km (measured from the calving front) of the EIS cavity ( Fig. 1)." Line 52: Not clear exactly what is being measured, from where to where. Annotate the figure and show these measurements so that it is explicit. This makes the figure look rather chaotic than helpful. Therefore, we consider the description "…most landward location of the current grounding line (8°6'W at the southernmost point) to the continental shelf. The distance to the grounding line is measured along the trough axis." to be sufficiently clear.
Lines 57-58: Did the Grobe and Mackensen paper really claim that the ice extended beyond the continental shelf break? That would be quite extraordinary. I thought they looked at slope records and IRD, but not evidence of actual ice extending that far.
In the Grobe and Mackensen paper on page 373 'Glacial Maxima' as well as in Fig. 12 they state that grounded ice extended across the continental shelf break of East Antarctica. However, the sediment cores taken in the EIS region were too short to grab any datable material from the LGM.

Lines 60-70: In addition to the model estimates of LGM timing here, are there any estimates from dated cores?
The only chronological constraint is mentioned in Grobe and Mackensen, 1992, who set the age of their cores to the Holocene. Further dated sediment cores have, to my knowledge, not yet been published.
->4.1.2 and Figure 3: Certainly sounds like MSGLs that are being described. However, there is nothing convincing in the figure. Zoom in, show more, consider color, mark with arrows, etc. As it is, the figure is not convincing. An overview of the found MSGLs are marked in blue in Fig. 3a. A zoomed-in section of the multibeam echosounder is displayed in Fig. 3c, and an example for the MSGLs in the echogram is shown in Fig. 3e. Since 3c and e show exclusively the MSGLs additional arrows were omitted. ->4.1.3: Many small moraines were noted in Antarctica much before the references cited. Yes, a variety of different kinds of moraines are described in the literature. Here, publications were selected, due to the use of similar marine geophysical methods and study areas, in order to allow a more direct comparison with our identified landforms. Many different moraine types are discussed in Shipp et al. (2002). However, there is no unambiguous indication of retreat moraines in their zone 3 and 4. They identified retreat moraines in their Zone 5, but their dimensions are not given, which does not allow a sufficient comparison with our landforms.
Lines 201-202: Calling on a core that is not included in the data of the paper, nor apparently published elsewhere, is not a fair line of evidence. We refer to the sediment core PS1385 (Figure 1 and Table 1), published in Grobe, H. and Mackensen, A.: Late Quaternary climatic cycles as recorded in sediments from the Antarctic continental margin, in: Antarctic Research Series, vol. 56, pp. 349-376, https://doi.org/10.1029/AR056p0349, 1992. They limit the age of the sediment core to the Holocene. The location of the core, where many iceberg plow marks are evident in the multibeam data, suggests that there is no longer undisturbed sediment deposition.
Lines 203-205: If evidence from slope cores indicates that ice reached shelf edge, but your MSGL data stops 11 km in and therefore you suggested ice maybe didn't reach the edge, how do those agree? Or, conflict? The MSGL are replaced by the iceberg ploughmarks at about ~10 km from the current ice shelf edge. The iceberg ploughmarks were formed after the ice shelf retreated. They have overprinted the seafloor and destroyed potential MSGLs that no conclusions can be made about whether the MSGLs (and thus grounded ice) were present further toward the continental shelf. MSGLs usually form under grounded ice in subglacial till. About the till thickness, on which the MSGLs are formed in the tough centre, we do not make any statement, since the marine geophysical data do not provide the needed in-depth data. In areas where the subglacial till deposits (with up to 45 m thickness) were detected with reflection seismics, MSGLs could not be resolved with our data. The removal of loose sediments by water flow beneath the ice shelf does not question that these are MSGLs, but it might explain why rarely drape can be found on top of them. Figure 1: Labels not clear in part a when text over ice boundaries. Define ice edge line in legend; differentiate grounding line from floating margin. Consider making this a three part figure as part a is currently not quite covering a large enough area to show people unfamiliar with Antarctica where the location is, but nor is zoomed in enough to show the region. Make an a and a b that are less/more zoomed in. Labels and ice edge will be added. The white infill represents grounded ice, which will be clarified. A three-part figure will be made.  Figure will be changed, so that more of the ice shelf is below sea level and the label will be moved to the left.