Dear Penelope How and co-authors,
As the editor of this manuscript, I had a detailed look at the 3 reviews, your response and the corresponding revisions of the revised version of the manuscript. In general the reviews were rather positive and highlighted the value and novelty of the presented datasets and related interpretation with regard to hydrology of tidewater glaciers. However, most reviewers also thought that a wider discussion of alternative controls on terminus flow/dynamics (frontal/geometry changes, calving, tides,…) should be included, and was somewhat lacking in the first version.

The authors undertook substantial revisions at the manuscript and the revised manuscript has been sent to re-review to one of the referees of the first round (Ref2) with the detailed review listed below.

According to the re-review and my own detailed analysis of the revised manuscript and author response, the authors addressed most of the major and most of the minor issues raised by the reviewers well.
However, the few more substantial concerns of reviewer 2 and reviewer 1 that refer to the point of ‘alternative controls on ice velocity (calving/front dynamics, ocean forcing, tides)’ were in the view of the referee and myself rather superficially or evasively addressed and moreover quite a number of additional minor editing or formulation issues were introduced with the revisions (see minor comments of re-review and editor below).

In the revised manuscript the effect of ‘marine influences, glacier dynamics, calving dynamics’ are now mentioned in the interpretation as other potential factors explaining for example the observed early season acceleration and potentially related processes but in general these statements remain extremely vague and lacks reference to existing literature/understanding, the potential mechanisms are often rather difficult to follow and the reader is repeatedly left with the sentence along the line of : ‘it cannot be further explored here, but could be an interesting focus in future work’.

I understand that that given the data available perhaps no detailed analysis of these additional controls can be expected or may be (as stated by authors) beyond the scope of this study.
However, leaving these alternative controls that vague weakens the interpretation/conclusion of this study and perhaps more importantly at least some of the existing understanding and literature on the general influence of front retreat/calving or ocean on flow speed etc… should be included, in particular as there is even some related literature on this on Kronebreen itself (Luckmann et al 2015, Schellenberger et al 2015 TC). Similar the analysis of the effect of tides on periodic drainage remains vague and could perhaps be improved or at least checked by considering relative frequencies of plume visibility and tides (see re-review below).

As the editor I suggest to address the following points on the revised manuscript:

1) Try to make the discussions of alternative controls on flow (front retreat/calving/ocean) a bit more specific, explain a bit better how these alternative controls may function and importantly include where possible existing understanding/knowledge and refer to the general (from other tidewater glaciers) and specific Kronebreen literature (Luckmann et al 2015, Schellenberger et al 2015 TC) there. It seems to me that we know quite a bit about these controls on flow. I do not think it requires an extensive discussion here but the most relevant mechanisms and literature should be mentioned and clarified.
The above refers roughly to p. 16 lines 18-22, p. 18 lines 3-5, p. 20 lines 12-14, p. 21 lines 18-22…)

2) better consider the the point on tidal forcing raised by the re-review (e.g. by considering relative frequencies of plume visibility and tides, see p. 22 lines 8-16).

3) Fig. 5: I agree with re-review that one can well see the acceleration (everywhere/almost uniformly) over the summer, but nor really well see the ‘upstream propagation’ (meaning wave of acceleration that propagates upstream). If this ‘upstream propagation is really crucial for the argument/interpretation maybe better way of illustrating the spatial flow evolution should be done (perhaps as re-review suggests relative change to first flow field and move current fig. 5 into appendix or so).

3) …try to avoid sentences that divert unexplored processes/effects to future studies (see also re-review below), as they do not add anything and give the impression that it is completely unknown (which is not always the case).

4) address carefully all the minor rather technical issues/comments by the re-review and editor listed below.


Additional minor editor comments:
p. 2 line 28: this sentence refers to alpine glaciers but the Kamb study is on tidewater glaciers (Columbia) . Kamb 1994 should certainly be cited but at the relevant place where subglacial hydrology of tidewater glaciers are discussed (e.g. end of same paragraph or on page 3).

p. 5 Fig 1 caption: style: rather say: ‘…the star marks the location of …’

p. 10 Fig. 2F: I would add symbols (dots or crosses) at each datapoint as currently one could get the impression that the data is continuous (in particular as the uncertainty band is also shown as continuous).

p. 14 line 10 this 6m increase refers probably to 09 JULY and not 09 September!

p. 18 line 17: a bit odd to refer to this period of 31 may – 16 august when time periods of the imagery in Fig. 5 are different. Maybe replace it with ‘between mid May and end of August’.

p. 21 line 18: I would delete the ‘key’ as this is speculation anyway.

p. 25 line 11: ‘Evidence suggests…’ what evidence, I guess data/observations from this study is meant here so say something along the line of : ‘Our observaations/analysis suggest…’

p. 25 line 19: ‘high rate of deformation’ this implies that basal motion is due to sediment deformation which you do not really know, I would rather say ‘high basal motion’.


Re-review by referee 2:
This is my second review of this manuscript, and although it has certainly improved since I first reviewed it, some of the changes and additions are superficial and do not deal sufficiently thoroughly with my initial suggestions (and those of the other reviewers). Also, there remains a tendency for unjustified speculation. On several occasions (e.g. regarding the potential effect of tides on periodic drainage of subglacially stored water) the speculation from the first submission remains, but an extra sentence along the lines of ‘Although we can’t tell with our data, it would be an interesting topic for future work’ has been added. I don’t think this is good enough. Surely for the specific case of tidal influence, a quick check of the relative frequencies of plume visibility and tides would be informative and is fairly simple to achieve?


Specific points:

Title: ‘hydrology pathways’ should be ‘hydrological pathways’

P1, L3-4: ‘water pressure’ should be ‘borehole water pressure’

P2, L3: ‘provides’ should be ‘provide’ (data are plural)

P2, L5: ‘across’ should be ‘beneath’

P2, L11: ‘marine’ plume seems an odd term to use here as these could be caused by wind-driven upwelling for example. How about ‘glacial’ or ‘meltwater’ plume instead?

P2, L22: Is it worth including some references for the observation of high pressures for most of the melt season?

P2, L24: ‘and’ should be ‘where’

P2, L26-27: This has also been observed at land-terminating margins of the Greenland Ice Sheet

P2, L27: ‘are’ should be ‘is’

P3, L4-5: I’m not quite sure what is meant here by the ‘two component structure’. I think this requires clarification.

P3, L6-7: The wording here is a little confusing. What if the implementation of the approach were perfect but the model didn't include key features of the real system? If model outputs no not match real-world velocities, is the representation of the subglacial environment really 'adequate'?

P3, L10-11: But lakes are also formed from surface melt, so this is not really 'additional'. This needs to be clarified.

P3, L11: Once drained (and therefore once a surface-bed connection has been made), the perched lakes become subglacially connected? I think this characterization is a bit confusing. How about surface melt-fed vs. subglacially-fed or something similar?

P3, L14: be clear that you mean supraglacial lakes here.

P3, L15: ‘contains entrained’ instead of ‘entrains’

P3, L22: ‘Detailed’ is vague. Do you mean higher temporal and/or spatial resolution?

P3, L25: ‘meltwater in the subglacial zone’ could be replaced with ‘subglacial meltwater’

P3, L26: The sentence beginning ‘This has…’ does not add anything useful – what other settings are there anyway?

P3, L27-28: ‘to make a channelized system become more efficient’ could be ‘to increase the efficiency of a channelized system’

P3, L29: ‘significant periods of time (i.e. decadal)’ should be ‘decadal timescales’

P3, L33: How do these long residence times this relate to surface uplift which typically recedes within 48 hrs? Is there any evidence (apart from modelling) which supports this idea of long residence times of subglacial water 'blisters'? Also, the excessive use of parentheses to characterise timescales is unnecessary (e.g. see my suggested simplification above).

P4, L10: Both satellite and time-lapse imagery are always temporally intermittent (unless you use video!). It is the relative rate of change in plume behaviour vs the temporal frequency of image acquisition which is important.

P4, L12-13: I don’t think this adds anything worthwhile.

P4, L27: I think the calving rate should be positive without the context of its net impact on glacier mass balance (which I suppose would be negative).

P4, L29: Consider replacing the second use of retreat with ‘receded’ to avoid repetition.

Figure 1 caption: ‘8 km LONG tongue’ otherwise not obvious which dimension you are referring to.

P7, L2: ‘underwent refreezing’ should be ‘refroze’

P7, L29: Both models should be cited here.

P8, L14: ‘up-glacier’ rather than ‘upper’

P8, L20: ‘is’ should be ‘are’

P8, L23-24: The fact that the GPS did not provide any extra useful information seems surprising - were the data simply too noisy?

P9, L18: ‘on’ should be ‘in’

P11, L22: How was the runoff ‘detected’? Surface lakes become visible or plume first reaches the fjord surface?

Figure 3 caption: You cannot know that the lakes are entirely drained from the camera angle… just that you cannot see any water in them.

P14, L29: ‘The relative timing of these components…’ could be ‘The relative timing of variations in these components…’

Figure 5: It is difficult to tell the difference between >2.4 m/d and no data. Could you use a more effective colour scheme?

Figure 5 caption: use ‘up-glacier’ instead of ‘upwards’

P16, L20: ‘enable ENHANCED glacier flow’ (after all, the glacier is already flowing…)

P16, L21: Some missing words? ‘but the influence of submarine ice melt on glacier dynamics could be…’?

P16, L23: ‘supported because of the coinciding observations’ could be ‘supported by coincident observations’

P16, L26: Other surface catchments perhaps? But not other catchments as determined by the combined bed and surface topography surely?

P18, L6: ‘this’ is a bit ambiguous. How about 'the sequence of events described above'

P18, L11: The hydraulic connection (rather than the distance per se) is key here: is the borehole connected to the channelised system and the adjacent regions which experience temporal variations in water pressure? From the data it looks like it is not (although you say that the water level in the borehole dropped substantially when the bed was reached).

P18, L16-17: No. The speedup propagates all the way up-glacier to the extent of the data shown. It would be useful (as I mentioned in my previous review) to have plots of the relative change in ice flow (i.e. percentage change for each pixel) using data from the earliest image pair as the baseline. This would show the speed-up much more clearly.

P18, L17: ‘appear to be’ should be ‘are’

P18, L27-28: But you have already admitted that the borehole is unlikely to be connected to the main hydrological system. Therefore you cannot make inferences about the extent of variations in meltwater storage at the bed from the borehole data.

P18, L25: ‘influenceS’

P18, L26: ‘aN’

P20, L13: The speed-up IS a change in glacier dynamics...!

P20, L21: ‘tongue is a heavily crevassed surface’ could be ‘tongue is heavily crevassed’

P20, L23: Why a possibility? Why don't you check? Timelapse? Satellite data?

P20, L27-28: Even with a distributed subglacial drainage system? Wouldn't you expect the plume to be more spread out along the calving front if this is the case? Do you see this?

P21, L13: ‘coincident timing’ could be ‘coincidence’

P21, L16: ‘thr’ should be ‘the’

P22, L9: Sufficiently melted the cavity wall for what?

P22, L10-11: This is really not worth including without some further analysis: for a start, does the pulsing show any variation on tidal frequencies?

P22, L32-33: But you have already admitted that the borehole is unlikely to be connected to the main hydrological system. Therefore you cannot make inferences about the diurnal subglacial water pressure variations from the borehole data.

P23, L8: But not every inch of the bed will be connected to the channels even in an ‘efficient catchment’ (although I’m not sure what that is)

P24, L24: Really unprecedented? How do you know? Within the last few years only?

P25, L1-2: ‘the basal pressure environment’ should be ‘basal water pressure’

Dear P. How,
I thank the authors for their careful and substantial revisions in response to a critical but overall positive re-review of the earlier revised version and my own editor-comments. The few more substantial points and minor editing issues have now been satisfactorily addressed and I am pleased to announce that the paper is accepted for publication in TC after correction of the very few minor technical points listed below.

At this stage I would also like to thank the authors for their excellent handling of revisions after the re-review.
Best regards

Andreas Vieli, the editor, 15th Oct 2017

p. 7 line 19: ‚...from...’ (instead of ‚fom’)

p. 8 line 8: maybe specify: ...2m SPATIAL resolution...

Fig. 2 (p. 10), caption: in C) it is not clear what the black crosses are (not in legend), are these refered to as the ‚max. plume extent’ as mentioned in caption??? Clarify.

p. 12 line 7: is ‚changeable’ the right word here, would ‚variable’ not fit better!

p. 12 line 9: i am just a bit curious here, that strong precipitation affects tides. Is it also related to a wind/storm surge?

p. 15 line 4: i think ‚...to the floatation level (...’ is more appropriate.

p. 22 line 17: atypical tidal fluctuations related to LOW PRESSURE? I miss a bit more explanation here (what is link?). is this related over a storm surge?

p. 26 line 27: i think the ‚at’ between ‚velocities’ and ‚throught’ should be deleted.

p. 27 line 19: to be consistent throughout, replace ‚unprecdented’ with ‚unusually’

p. 28 line 10: i think the ‚to’ between ‚tentatively’ and ‚in previous years’ should be deleted.