1) Because this study confines itself to a rather specific portion of the whole Antarctic Peninsula ‘region’, the authors are cautioned to avoid vague terms such as ‘region’ (see Abstract, page 1, line 11) when referring to only the very northern part of the contiguous AP and none of the adjacent islands.
2) ‘Seal Nunataks’ is used in the abstract to provide a geographic limit to the study area (page 1 line 13) but should refer to Fig. 1 as it is not labeled on the other maps.
3) The authors are similarly cautioned to be specific when referring to the ‘study period’ given that the title states that the study period is ‘since 1985’ but the velocity data covers a much shorter period, especially for some glaciers, and some regions only had ‘area changes’ since ~1995.
4) Similar to #1, the authors must be clear that the warming that has been observed on the ‘Antarctic Peninsula’ must be limited to the ‘northern’ AP and its outlying islands given where the majority of the data sets are located (page 1 line 26).
5) The use of a single reference to document the loss of ice shelves, page 2 line 10, appears a little uncharitable to the many researches who have contributed a great deal of insight and analysis to this particular topic along and across the AP. Even though additional references are added below, the list still seems inadequate and does not give the reader a useful sense of what shelf areas were lost and when.
6) Related to #5, close inspection of Figure 1 helps somewhat with this issue but the placement of the ‘keys’ on top of the area changes is unhelpful. Further, dashed lines would help differentiate some of the colors that are very similar. Oddly, it is only by closely reading the text that one realizes that the northern end of the contiguous AP was studied but lacked enough velocity data to be included (those basins are included in Figure 5 for area change). It isn’t clear why the basins are cropped off.
7) On page 2, line 23, given the number of studies in this section, it isn’t clear which ‘authors’ are being discussed.
8) Similar to #1, the term ‘north-eastern’ appears to mean the northern AP’s eastern glacier basins on page 2, line 25. Also, ‘as a consequence to’ on line 26 is unclear.
9) The phrase ‘not homogenous’ (page 2, line 28) seems rather obvious. One assumes that the authors mean this in both space and time and this should be linked back to the different times that glaciers in the area have become marine- as opposed to shelf-terminating.
10) The phrase “Previous studies often only cover a specific period or region, or focus on one particular aspect of glacier change.” On page 2 lines 29-30 also appears to be uncharitable to other researchers who worked with what data sets were available to them at the time. In time, this study will also be superseded by new data and techniques so I suggest rephrasing the intended meaning.
11) Similar to previous concerns, ‘northern-most’ (page 3, line 5) is quite imprecise and requires all outlying islands of the AP to be ignored. The analysis of Huber et al. 2017 makes it quite clear how much area of the AP has been excluded in this study.
12) Please review all superscripts for consistency (page 3, line 8). Also, should ‘yr’ or ‘a’ -1 be used?
13) Given their prominence on the figures and also as the source areas for many glaciers, the ‘plateau regions’ should be referenced (page 3, line 12).
14) The Prince Gustav (no hyphen) shelf had left the channel before 1995 according to ADD and also the USGS I-2600A map (page 3, line 15).
15) The phrase ‘long-term’ is not appropriate for ~20+ year records (see previous comment on ‘study period’).
16) Given the use of percentages in a number of places in the paper is seems appropriate to contrast the ’11,000 km2’ area (page 3, line 26) against the whole area of the AP including its islands. Also ‘altitudes’ should probably be ‘elevations’.
17) There are too many ‘word choices’ to point them all out but ‘substituted’ should be ‘replaced’ (page 3, line 29).
18) Please revise capitalization on page 4, lines 8-9. Also line 26.
19) One assumes that the ‘100m’ (please check spacing for units throughout the text) pixel spacing requires resampling given the native resolutions now listed in Table 2 as ‘nominal ground resolution’* although one has to wonder if this is also due to incidence angle on the AP’s ‘jagged’ topography. Please clarify.
20) A requested ‘summary’ of the uncertainty in the ASTER DEM has been inserted on page 5, line 25. Unfortunately, a quick examination of Cook et al. (2012) Figure 5, the paper that is the source of the elevation bias, shows that the bias number is itself biased towards the much more extensive ICESat coverage far to the south (to 70°S) of this paper’s study area. With the vast majority of the ICESat to DEM comparisons apparently coming from lower slope areas of the AP, it is highly unlikely that the given numbers apply to the 63-65°S portion of the AP. Further, no attempt appears to have been made to show if the bias varies as a function of slope in the study area. One has to wonder why this was not done given the importance of the DEM to the geometric aspects of the study as well as the potential to impact the velocity data. In short, a much more realistic assessment of the DEM’s accuracy in the study area is not yet available. See also Huber et al’s (2017) more conservative estimates.
21) The text on page 6, line 15 needs clarification: “close to the terminus of each glacier basin, behind the maximum retreat state of ice front position in the observation period”. It is pretty clear what is meant but this phrasing is awkward.
22) It would be useful to quantify what is meant by ‘very high’ and ‘significantly lower’ on page 6, lines 6-8. Also, does the mass input depend at all on basin orientation or only on the hypsometry and elevation (lines 8-9).
23) The sentence at the end of page 7 and top of page 8 still needs some sort of analogy or further explanation to make it accessible to the average reader. Even the most dedicated readers will be unlikely to dive as deep as appears to be needed to see what is being done to the raw input numbers. In addition, it still seems relevant to point to any other study in glaciology that has derived useful results from a related ‘sorting’ technique.
24) Area changes for the ‘ice shelf loss glaciers’ needs to be separately called out on page 8, line 5, given that are ‘after 1995’ not since ‘1985-1989’. Interestingly, this date range suggests the variability in temporal resolution of the area change values going into the cluster analysis, also an issue with the temporally variable velocity values as shown in S1-74.
25) See previous comment on ‘percentages’ but the actual area change values should be given on page 8, lines 11-13.
26) The use of the word ‘trends’ when referring to what are simply plots of the velocity data is problematic for a number of reasons. In some case, there simply isn’t enough data to even estimate a trend (e.g. S4, S6, S8) and even when there is more data, it is often so unevenly temporally sampled (S27, S28, S56) as to be impossible to discern a trend (or as is discussed later, a pattern). Further, there is also a great deal of concern that signal vs noise (apparent pattern vs error bars) is not being taken into account in the results section of this paper.
27) Please clarify “On average the ice flow in the study region increased by 1.6%, but the glaciers in the individual sectors showed on average significant change.” on page 9, lines 7-8. Please give velocity change values as well as % so as to save to save the reader from having to also read the supplement.
28) The sentence “The presented average flow speed change values are based on the observed changes of all glaciers in the respective sector (Table S1), ignoring the different size of the individual glaciers.” leads to wondering if size classes in each sector might provide more insight?
29) Please change the term ‘shrinkage’ throughout as it suggests a 3-dimensional change in volume rather than a change in area alone (page 10, line 3).
30) The term ‘theory’ should be replaced with ‘hypothesis’ and given how speculative this is, given the large distances to the nearest met stations, I think the editor should consider excising this speculative section. Note, unpublished (as of yet) studies are suggesting that the ‘cooling’ was a problematic sampling of the longer-term record now that 2016 and 2017 data is becoming available.
31) The ‘clear positive velocity trend’ (page 10, lines 16-17) does not appear to be supported by the figures in S57-74 in my opinion. See the previous comments on ‘trend’ and signal vs noise’.
32) Please explain how Skvarca et al. (1998) saw a cooling trend in the 21st century (page 11, line 6).
33) The ‘peaked’ trend for TPE10 Glacier (page 11, line 15, is a very clear example of over-interpreting insufficient data as is Aitkenhead Glacier (S3).
34) Perhaps I don’t understand what ‘frontal advance’ means (page 11, line 22) given 5-year averaging but the glaciers mentioned both show continued area losses in the referenced plots.
35) Please give the ‘comparable values’ for the two analyses on page 12, line 11.
36) A ‘potential peak in flow speed’ (page 12, line 25) appears to be unnecessary speculation as it ‘cannot be detected’.
37) Pyke Glacier is within the APPE group so a reference to Table 1 seems useful (page 12, line 28).
38) The opening paragraph on page 13 seems muddled. Also, the term ‘jagged’ for the western coastline seems inadequate given the point is to give context for the ‘heterogeneous’ changes observed in sector ‘West’. See the previous review for a concern about the potential orographic impact of large islands on the west side as well as an earlier comment here on slope aspect vs solely elevation/hypsometry.
39) Group1 ‘needs some space’ (page 13, line 21).
40) There is something missing around ‘dissimilarities’ on page 13, line 18, perhaps ‘matrix analysis’ would be appropriate to add here.
41) It seems odd not to reference the previous study by the lead author at the end of the first sentence of the Conclusions.
42) It would appear to be more accurate to say higher ‘overall’ glacier flow given the heterogeneous response (page 15, line 7) and there is also a problematic use of ‘trends’ here as well.
43) It was my understanding from the paper that ‘Larsen Inlet, Larsen A’ glaciers had area changes assessed since ~1995 (not relative to 1985), page 15, lines 10-11.
44) The phrase ‘cooling since the mid-2000s’ (page 15, line 16) is inconsistent with what Turner and Oliva et al. published. Also, ‘1960s’ seems incorrect. Please check.
45) There would usefully be some discussion of what is and is not possible with the data sets available to date in the last paragraph. It is clear to this reader that even with a very serious effort to understand the variability of this region, there are pretty significant deficiencies in our data sets.
Figures showing LIMA need not have a copyright symbol, just a credit to the agencies involved.
Figure 2 has an order of magnitude of velocity difference between panels C and E and I remain concerned that this makes it very difficult to interpret these plots.
Figure 3 is improved but is still very difficult to read even with much magnification of the pdf files.
Figure 4, check the caption for a typo ‘lest’? Also, please darken the area labels on the Y1 axis to emphasize how much area remains in each sector.
Figure 5’s key should not have dashes and minus signs, please find some other way to show the ranges and consider adding a ‘+’ for the one positive color. Also remove ‘regional’ before ‘sector’ in the caption.
Figure 7, one presumes ‘Group N’ is ‘Group Number’ or simpler ‘Group’.
Table 3 shows two categories ‘stable’ and ‘fluctuating’ as having the same numeric rating which makes one wonder even further about the cluster analysis. Did I miss discussion of ‘fluctuating’ in the text? Are these distinctions meaningful given the temporal resolution of the velocity data for many glaciers? Please clarify.
Supplement, page 1, Figure S74 should be S75 for the Drygalski
S17, add a space in Arron Icefall’s label, consider increasing font sizes for axis labels |
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